tit-bits of useful information

General

Emil von Behring, recipient of the first Nobel Prize for medicine, was born on March 15, 1854, in the small village of Hansdorf, West Prussia (Germany). Behring became known as the "Saviour of the Soldiers" as well as "Saviour of the Children."
In 1884, Koch, drawing on the ideas enunciated in 1840 by his teacher Jacob Henle, conceptualized the relationship between individual infectious agents and specific diseases as a series of axioms commonly known as the Henle-Koch postulates.
Antony van Leeuwenhoek, pronounced as "layu-wen-hook" was a tradesman of Delft, Holland. His father was a basket-maker, while his mother's family were brewers.
Louis Pasteur developed three attenuated vaccine- chicken cholera, anthrax and rabies.
The Transmission Electron Microscope (TEM) was developed by Max Knoll and Ernst Ruska in Germany in 1931. The first Scanning Electron Microscope (SEM) debuted in 1942 with the first commercial instruments around 1965.
Confocal microscope uses laser to light one plane of a specimen at a time; specimens stained with fluorochromes. It uses small, pinhole aperture to eliminate blurring of image and improved resolution. It is usually used in conjunction with a computer to produce 3D images and sections of cells and components. Images can be viewed in different orientations.
Oil immersion lens has a short focal length and a small numerical aperture. Thus, it has to be very close to the object in order to get as many as possible of the divergent rays from the object. Because of its narrow aperture, strong illumination of the object is necessary.
In brightfield microscopy, where a coiled filament tungsten lamp is used, the glare produced by the filament is prevented by focusing the light on the substage condenser rather than on the object. This is Kohler illumination.
The resolving power of human eye (0.2µm) is limited because the sensory endings of the optic nerve in the retina are relatively large.
Methanol fixation preserves the morphology of RBCs. Slides are overlaid with 95% methanol for one minute, allowed to run off and slides are air-dried.
Basic fuchsin is more soluble in phenol than in water. Phenol in turn is more soluble in waxes and lipids such as those present on tubercle bacilli.
Carmine (obtained from female cochineal insects- Coccus cacti) and hematoxylin (obtained from Mexican tree Haematoxylon campeachianum) were natural dyes used by early pathologists. Orecin and litmus are extracts from lichens. Coaltar derivative dyes were the work of William Perkin, a british chemist.
Acidic dyes have anionic chromophores (sodium⁺ eosinate^-) whereas basic dyes have cationic chromophores (methylene blue+ chloride-).
Vital staining is the staining of living cells. Intra-vital staining is the staining of living cells whilst still a part of the body. Supra-vital staining is the staining of the living cells when removed from the body.
The fluorescent actin staining (FAS) test, which uses fluorescein-conjugated phalloidin (an actin-specific fungal toxin) to bind filamentous actin in the so-called attaching and effacing AE lesion, is highly sensitive and specific for AE lesion-forming EPEC, EHEC, H. alvei, and C.freundii.
Originally isolated from Streptomyces venezuelae, chloramphenicol is now made synthetically. It binds to the peptidyl transferase enzyme to inhibit transfer of the growing polypeptide to the next amino acid, thereby inhibit bacterial protein synthesis.
Tetracycline was originally obtained from Streptomyces species; Rifampicin from Streptomyces mediterranei; Aztreonam from Chromobacter violaceum; Imipenem from Streptomyces cattleya; Vancomycin from Streptomyces orientales; Clindamycin from Streptomyces lincolnensis; Erythromycin from Streptomyces erythreus ; Polymyxin from Bacillus polymyxa; Bacitracin from Bacillus subtilis; Amphotericin from Streptomyces nodosus; and Nystatin from Streptomyces noursei.
Gentamicin is produced by the actinomycete member, Micromonospora echinospora/Micromonospora purpureochromogenes. Micromonospora inositola produces the antibiotic sisomicin. Micromonospora inyonensis produces the antibiotics mutamicin and netilmicin. Other aminoglycosides aminoglycoside names that end with mycin to highlight the different species from which they originate (e.g. neomycin and streptomycin, produced by Streptomyces spp.).
Clavulanic acid is produced by Streptomyces clavuligerus. It is a ß-lactam structurally related to the penicillins and possesses the ability to inactivate a wide variety of ß-lactamases by blocking the active sites of these enzymes.
Sulfonamides were introduced as chemotherapeutic agents by Domagk in 1935. Bacteria which are almost always sensitive to the sulfonamides include Streptococcus pneumoniae, beta-hemolytic streptococci and E. coli.
The sulfonamides and Trimethoprim are inhibitors of the bacterial enzymes required for the synthesis of tetrahydofolic acid (THF). Sulfonamides are structurally similar to para aminobenzoic acid (PABA), the substrate for the first enzyme in the THF pathway, and they competitively inhibit that step. Trimethoprim is structurally similar to dihydrofolate (DHF) and competitively inhibits the second step in THF synthesis mediated by the DHF reductase.
Quinupristin and dalfopristin are streptogramin B and streptogramin A antibiotics, respectively, whose combination (pristinamycin) in a 30:70 ratio acts synergistically. It is used mainly for vancomycin-resistant Enterococcus faecium and multiresistant staphylococci.
Tigecycline is the first glycylcycline to be launched and the first new tetracycline analogue since minocycline over 30 years ago. It evades the efflux pumps,which account for most acquired resistance to tetracycline and minocycline in Enterobacteriaceae and Acinetobacter spp.
Nitrocefin is a chromogenic cephalosporin developed by Glaxo research limited. It exhibits rapid colour change from yellow to red as the amide bond in beta-lactam ring is hydrolysed by beta-lactamase.
Metronidazole is a synthetic derivative of Azomycin (a nitroimidazole), which was obtained from extracts of Streptomyces spp. The antibacterial activity of metronidazole was discovered by accident in 1962 when metronidazole cured a patient of oth trichomonad vaginitis and bacterial gingivitis.
Cephalothin and cefazolin serves as the spectrum class representative for first generation oral and parenteral cephalosporins.
Vancomycin belongs to the glycopeptide class of antibiotics, which are effective against gram-positive organisms. In contrast, gram-negative bacteria are intrinsically resistant to glycopeptides because of their impermeable outer membrane. Glycopeptides are composed of a hepta-peptide backbone that is substituted with five to seven aromatic rings and different sugars. In contrast to penicillin, which directly binds to and inhibits the transglycosylases/transpeptidases involved in cell-wall biosynthesis, vancomycin binds to the substrate of these enzymes.
The filament of bacterial flagella is a long (1 - 10 µm) hollow protein tube that is made up of 11 rows of flagellin subunits. Flagellin has a molecular weight of 40,000 Daltons; has a primary amino acid sequence containing about 365 amino acids.
Use of xylene to dilate the vein (in animals) is not recommended as it causes skin rashes, sloughing etc. 10% of circulating blood can be drawn every 3-4 weeks without any harm to the animal. 7.5% of blood may be collected every week from rabbit without any harm.
Bacteriocins are named after the species it is produced in and the plasmid is named after the specific bacteriocin it encodes. A naturally occurring plasmid only encodes for one type of bacteriocin. Colicins produced by Esherichia coli, function by disrupting the cell membrane of surrounding Esherichia cells.
A chemically-defined (synthetic) medium is one in which the exact chemical composition is known. A complex (undefined) medium is one in which the exact chemical constitution of the medium is not known..
Agar is an unbranched polysaccharide obtained from the cell membranes of some species of red alagae (Gelidium and Gracilaria) or seaweed (Sphaerococcus euchema). It is also known as kanten, China grass or Japanese isinglass. It is a heterogenous mixture of two classes of polysaccharide; agaropectin and agarose.
Selenite Broth was devised by Leifson, who demonstrated that selenite was inhibitory for coliforms and certain other microbial species, such as fecal streptococci, present in fecal specimens and, thus, was beneficial in the recovery of Salmonella species.
Alfred Theodore MacConkey (1861-1931) was the British bacteriologist who developed MacConkey's agar, a selective medium that is used in the diagnosis of enteric pathogens.
Stuarts medium consists of buffered semisolid agar devoid of nutrients and contain sodium thioglycollate as reducing agent. It maintains a favourable pH, prevents drying, prevents oxidation and autolysis of pathogen.
The pH reading of a hot solution will be different than that taken at room temperature.
Mutant strains of bacteria that require some growth factor not needed by the wild type (parent) strain are referred to as auxotrophs.
LAL assay for endotoxin detection is sourced from amebocytes of Horseshoe crabs (Limulus polyphemus) permitting detection of endotoxin in picogram quantities. Sensitivity of the LAL reagent toward endotoxin is further increased by including low concentrations of divalent and monovalent cations. Calcium and manganese ions are the preferred divalent ions.
Quality control strains for coagulase test: Staphylococcus aureus 25923 Positive; Staphylococcus epidermidis 12228 Negative. Quality control strains for Oxidase Test: Neisseria gonorrhoeae 43069 Positive; Escherichia coli 25922 Negative.
A 0.5 McFarland standard is comparable to a bacterial suspension of 108 cfu/ml. It is prepared by mixing Barium chloride in sulfuric acid. McFarland standards are available in a range of 0.5 to 8.
Freeze drying (also known as lyophilization) works by freezing the material and then reducing the surrounding pressure and adding enough heat to allow the frozen water in the material to sublime directly from the solid phase to gas.
Microaerophilic conditions can be created by adding a small concentration of agar to a liquid medium. By preventing oxygen at the surface from being dispersed throughout the liquid by circulating convection currents, agar serves to create microaerophilic environment 1-2 cm below the surface of the medium.
L-alanine-4-nitroanilide test is positive for gram negative bacteria. String test with 3% KOH is positive for gram negative bacteria.

Bacteriology

Proteus species infection causes release of ammonia and carbon dioxide by urease action. The ammonia released is able to damage the glycosaminoglycan layer, which protects the urothelial surface against bacterial infection.
The first-line therapy for H pylori eradication is usually based on a combination of two antibiotics (amoxicillin plus clarithromycin/metronidazole) and a proton pump inhibitor (eg, omeprazole).
Normal ASO titre levels in children aged 5-12 years is <333 IU and those in young Adults is <200 IU
Protein A is a surface constituent of S. aureus as well as a secreted product, which binds to the Fc portion of immunoglobulins. By binding to Fc portion of IgG, phagocytosis via Fc receptors may not occur because of steric hindrance. Protein A also has anti-complementary role.
Diphtheria toxin is coded by the phage tox gene. It ADP-ribosylates elongation factor (EF2) in ribosomes, thus inhibiting protein synthesis. Pseudomonas exotoxin A has an similar mode of action to diphtheria toxin.
The cholesterol-dependent cytolysins (CDCs) are a large family of pore-forming toxins that are produced by more than 20 species from the genera Clostridium, Streptococcus, Listeria, Bacillus, and Arcanobacterium.
Pneumococcal autolysin is a peptidoglycan degrading enzyme that is released by bile from the cell membrane. It binds to a choline-containing teichoic acid attached to the peptidoglycan. The autolysin then digests the bacterial cell wall resulting in lysis of the cell.
The four resistant phenotypes are that are observed with S. aureus are methicillin-susceptible S. aureus/glycopeptide-susceptible S.aureus [MSSA/GSSA], MRSA/GSSA, hGISA/MRSA, and GISA/MRSA). S. aureus strains ATCC 29213 (vancomycin susceptible), ATCC 700698 (hVISA; Mu3), and ATCC 700699 (VISA; Mu50) are used as controls.
Psittacosis is a zoonosis caused by infection with Chlamydophila (formerly Chlamydia) psittaci, an obligate intracellular bacterium. C. psittaci is divided into 8 serovars (AF, M56, and WC) and at least 9 genotypes. Sequence analysis of the outer membrane protein A (ompA) gene is the most accurate method for identifying all known genotypes.
Obligate anaerobes are bacteria that cannot survive in the presence of a high oxidation-reduction potential (redox potential) / high oxygen content. During metabolism bacteria can produce toxic bi-products from oxygen (including superoxide radicals and hydrogen peroxide). Strict anaerobes lack certain enzymes (including superoxide dismutase and catalase) that detoxify these products.
Yersinia pestis bacterium is named for the French researcher, Alexandre Yersin, who identified the organism in 1895. The organism has undergone large-scale genetic change and has acquired genes from other bacteria and viruses including ahesins, secretion systems and insecticidal toxins.
Clostridium septicum is associated with colonic carcinoma and can be isolated from blood. Spontaneous forms of infection are believed to be associated with colonic malignancy, acute leukemia or cyclical neutropenia. Unlike C perfringens, C septicum is aerotolerant and can infect normal tissues.
The mycolic acid in the cell wall of Mycobacteria has an affinity for the fluorochromes auramine and rhodamine.
Mycobacterium, Pseudomonas, Neisseria, Brucella are aerobic. Campylobacter requires 5-10% CO2 and not more than 6% oxygen. Candle jar provides 3% CO2.
Group B Streptococcus, Listeria sps and Gardnerella vaginalis are positive for Hippurate hydrolysis. Esculin is hydrolysed by Listeria, some Enterococci and viridans Streptococci.
The first human pathogen isolated was Neisseria gonorrheae by Albert Neisser in 1879.
For typhoid fever, Watson procedure of using blood clot for culture has been found very useful.
In cases of suspected subacute bacterial endocarditis, fungemia or brucellosis, blood cultures are usually held for 2-4 weeks.
Borrelia burgdorferi contains linear plasmids.
Pseudocoagulase is the prothrombin activation by metalloprotease (e.g.,Bacteroides melaninogenicus, Staphylococcus) giving flase positive results. Proteolytic activation of prothrombin by a bacterial protease can be the cause, Staphylocoagulase activity can be separated from that of pseudocoagulase after addition of proteases inhibitors or heparin. Peptocoagulase is produced by bovine clinical isolates of Peptococcus indolicus. Yersinia pestis is also known to produce a coagulase.
Media with 10-30% sucrose in blood culture bottle have been recommended for recovery of small number of organism or for recovery of cell wall damaged bacteria in patients receiving antimicrobial therapy.
All members of family Enterobacteriaceae have a common O14 antigen.
Antibiotic susceptibility testing by disc diffusion for Streptococcus pneumoniae and beta-hemolytic Streptococci must be done on cation supplemented Mueller Hinton agar with 5% lysed horse blood.
Gamma-Favre are basophilic inclusion bodies found in granuloma inguinale.
Some autotrophic soil bacteria that are inhibited by organic substance such as agar are cultured on silica gel. This is also useful to grow bacteria that liquifies agar.
Some bacteria are not definitely gram positive unless cultivated in the presence of 5% blood or serum. Gram reaction also depends on acidity or alkalinity of the suspending fluid as well as the age of the bacteria and exposure to cell wall acting agents.
Salmonella Vi polysaccharide vaccine prepared from Ty2 strain contains 25µg of purified Vi polysaccharide in a single dose of 0.5 ml injection. The single dose is followed by a bosster dose every two years for continued exposure.
Cultures of gonococci and meningococci need to be subcultured every 2-3 days and must be kept at a temperature of 37oC in atmosphere containing 5% CO2.
In 1993, the genera Bartonella and Rochalimaea were united, with Bartonella having nomenclatural precedence over Rochalimaea. Thus, B henselae is currently recognized as the causative agent of Cat Scratch Disease (CSD).
Actinomadura is a filamentous bacterium found in soil. Although it was once believed to be a fungus, the information later attained about its ultrastructural cellular properties showed that Actinomadura is in fact an aerobic actinomycetes. Actinomadura madurae, Actinomadura pelletieri, and Actinomadura dassonvillei are the species included in the genus Actinomadura. Actinomadura madurae is distinguished from A. pelletieri by its ability to produce acid from cellobiose.
The genus Bartonella includes 19 distinct species, of which at least 6 are responsible for human disease (B henselae, Bartonella bacilliformis, Bartonella quintana, Bartonella elizabethae, Bartonella vinsonii, Bartonella koehlerae). These species are small, fastidious, intracellular Gram-negative bacilli that are aerobic and oxidase-negative. The organisms are most easily visualized by using a Warthin-Starry silver impregnation stain or a Brown-Hopps tissue Gram-stain. Two main genogroups of B henselae have been identified in humans and cats: Houston-1 and Marseille (also known as genotype II). These 2 genogroups are further subdivided into 4 variants: Marseille, CAL-1, Houston-1, and ZF-1.
Like a majority of V. cholerae non-01 isolates, but unlike V cholerae 01, V cholerae 0139 isolates possess a capsule. It is thought that, as in other capsulated Vcholerae non-01 serogroups, the presence of a capsule on V. cholerae 0139 may confer increased virulence to the organism, such as resistance to serum killing and capacity to produce bacteremia.
Sand desiccation is a convenient and cheap method for the long-term preservation of streptococci. Group A streptococci can be preserved by sand desiccation and stored at 4 degrees to 10 degrees for several years.
Rapid latex agglutination assay, detecting PBP2' (also called PBP2a) 7, in isolates of Staphylococcus, as an aid in identifying methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci has high sensitivity and specificity. Latex particles sensitized with a monoclonal antibody against PBP2a will specifically react with methicillin-resistant staphylococci to cause agglutination visible to the unaided eye.
Recently, based on phylogenetic evidence, the Chlamydiaceae family has been split into two genera (Chlamydia and Chlamydophila) encompassing three (Chlamydia trachomatis, Chlamydia suis, Chlamydia muridarum) and six (Chlamydophila abortus, Chlamydophila psittaci, Chlamydophila pneumoniae, Chlamydophila pecorum, Chlamydophila felis, Chlamydophila caviae) species, respectively.
Cefsulodin-irgasan-novobiocin (CIN) agar is highly selective for Y. enterocolitica. It requires 18-20 hours of incubation at 25°C to create unique colony morphology. Y enterocolitica appears as 0.5- to 1.0-mm colonies with a red "bull's-eye" and a clear border. Use of this medium allows differentiation between Y enterocolitica and Y enterocolitica- like isolates. Researchers have identified 34 serotypes and 5 biotypes; most human strains are biotype 4, serotypes that most clearly are pathogenic to humans include serotypes O:3, O:5, O:27, O:8, O:9, and O:13.
Polychromatic differential stains such as Wayson and Wright-Giemsa provide contrast staining Yersinia pestis so that bacteria, tissue, and blood cell components are easily seen. Basic fuchsin and methylene blue in the Wayson stain bind to the bacterial cells which, upon staining, appear as pink-blue cells with granules at end of the cell, thus making the cell look like a closed safety pin. Wright-Giemsa stain, binds to Y. pestis cells in much the same way as methylene blue, yielding bipolar-staining Y. pestis cells.
Enrichment of medium with 6% sheep red blood cells instead of the standard 5% provides more nutrition for Yersinia pestis and shortens the incubation period. Under 4X enlargement, after 48-72 hours of incubation, colonies have a raised, irregular "fried egg" morphology, which becomes more prominent as the culture ages. Colonies also can be described as having a "hammered copper," shiny surface. There is little or no hemolysis of the sheep red blood cells.
Whipple's disease, was first recognized as a new disorder in 1907 by the American pathologist George Hoyt Whipple. The bacterium associated with Whipple's disease is Tropheryma whipplei. The leading symptoms of Whipple's disease are weight loss arrhea, and arthropathy. The organism was named Tropheryma from the Greek trophi (food) and eryma (barrier), because of malabsorption frequently observed in the disease.
The name "enterococcus" is derived from the French word entérocoque, which was used to describe the enteric origin of this gram-positive coccus. In the mid-1930s, enterococci were classified as Streptococci. In the mid-1980s, nucleic acid studies indicated that enterococci were not closely related to streptococci, so a new genus Enterococcus was proposed.
Three Vancomycin Resistant Enterococci (VRE) phenotypes have been designated VanA, VanB and VanC on the basis of the minimal inhibitory concentration in VRE and susceptibility to teicoplanin. The VanA and VanB phenotypes differ in that VanA is resistant to teicoplanin, whereas VanB is not resistant because the VanB resistance pathway is not activated by teicoplanin.
Typhoid Vaccine Live Oral Ty21a vaccine contains 2-6x109 colony-forming units of Viable S. typhi Ty21a, 5-50x109 bacterial cells of Non-viable S. typhi Ty21a per capsule along with other constituents such as sucrose, ascorbic acid, amino acid mixture, lactose and magnesium stearate.
Several bacterial properties (including P fimbriae, type 1 fimbriae, hemolysin, aerobactin, serum resistance, and the Kl capsule) are fairly well established as virulence factors in acute, symptomatic E. coli UTI.
The Klebsiella pneumoniae isolates are classified phenotypically as mucoid or nonmucoid. Colonies of hypermucoviscous strains give positive string test when touched with a loop and lifted vertically from the surface of the agar plate. Mucoid phenotype is defined as being present when a string-like growth is observed to attach to the loop as it is lifted from the plate. Presence of the rmpA gene (rmp = regulator of the mucoid phenotype) can be detected by DNA dot blot hybridization or PCR.
World Health Organization (WHO) International Escherichia and Klebsiella Reference Centre is in Copenhagen, Denmark.
Vibrio parahaemolyticus was first identified as a cause of food-borne illness in Japan in 1950, when 272 individuals became ill and 20 died after the consumption of semidried juvenile sardines. It causes three major syndromes of clinical illness, i.e., gastroenteritis, wound infections, and septicemia. Sometimes the diarrhea is bloody, with stools described as "meat washed" since the stool is reddish watery stool.
V. parahaemolyticus strains that are isolated from diarrheal patients produce either the thermostable direct hemolysin (TDH), the TDH-related hemolysin (TRH), or both, while hardly any isolates from the environment have these properties. An isolate producing TDH is referred to as Kanagawa positive and can be identified by ß- hemolysis on a special agar known as Wagatsuma blood agar. TDH has been shown to have hemolytic, enterotoxic, cardiotoxic, and cytotoxic activities.
Most Vibrio species are sensitive to O/129 (2,4-diamino-6,7-diisopropylpteridine) 150 µg discs but species differ with 10 µg discs (some strains of V. cholerae O1 and O139 may be resistant to both disc contents).
Discovery of the E. coli verocytotoxin (VTs) was done by Konowalchuk and colleagues during the late 1970s in Canada. While investigating the usefulness of Vero (African green monkey kidney) cells for detecting the heat-labile enterotoxin (LT) of E. coli, they observed that culture filtrates from some E. coli strains produced a profound irreversible cytopathic effect in Vero cells in contrast to the reversible cytotonic effect of LT.
Eighty-six percent of nosocomial pneumonias are associated with mechanical ventilation and are termed ventilator-associated pneumonia (VAP). VAP caused by Pseudomonas aeruginosa, Acinetobacter spp., and Stenotrophomonas maltophilia tend to have high mortality.
Probiotics are live microbial organisms that are administered in supplements to benefit the host. They are taken by patients, administered by health care professionals, and prescribed by physicians. Some of the probiotics used in adults with diarrhea include Lactobacillus reuteri, Saccharomyces boulardii, Lactobacillus casei and Bifidobacterium bulgaricus. L acidophilus, L reuteri, L rhamnosus, B bifidum, or their combinations are used in children.
The current genus designation, Acinetobacter is derived from the Greek word 'akinetos' implying 'nonmotile'. This was proposed by Brisou and Prevot in 1954 to separate the nonmotile from the motile microorganisms within the genus Achromobacter.
Actinobacillus actinomycetemcomitans was first described by Klinger in 1912. The species was so named because, until 1964, it had been reported as being isolated exclusively in cases of actinomycosis or actinomycotic-like lesions. In 1959, Heinrich and Pulverer demonstrated that A. actinomycetemcomitans was a constituent of the normal mouth flora. It is is grouped in the HACEK group of bacteria, along with Haemophilus influenzae, H. parainfluenzae, H. aphrophilus, H. paraphrophilus, Cardiobacterium hominis, Eikenella corrodens and Kingella kingae.
Most Aeromonas strains produce tan to buff-colored colonies on Trypticase soy agar when incubated at 25°C for 2 to 5 days. Identifying tests include reactions the presence of cytochrome oxidase and nitrate reductase, fermentation of D-glucose and trehalose, failure to utilize mucate, and the inability to produce acid from D-arabitol, dulcitol, erythritol, and xylose.
Cystic fibrosis, a chronic pulmonary disease caused by a recessive autosomal gene in the Caucasian population is characterized by a vicious cycle of inflammation and infection. The pathogens of CF include Staphylococcus aureus, nontypeable Haemophilus influenzae, Pseudomonas aeruginosa, and Burkholderia cepacia. Several additional potential pathogens have been recovered from CF patients, including nontuberculous mycobacteria, Stenotrophomonas maltophilia , and Alcaligenes xylosoxidans.
Actinomyces species are frequently isolated from clinical specimens in mixed culture with Actinobacillus actinomycetemcomitans, Eikenella corrodens and species of Fusobacterium, Bacteroides, Capnocytophaga, Staphylococcus, Streptococcus and Enterococcus.
Colonies of Actinomyces graevenitzii and Propionibacterium propionicum on blood-containing media fluoresce red under long-wave (366nm) UV illumination.
Anaerobic Actinomyces may be isolated using Actinomyces selective agar with metronidazole 10mg/L and nalidixic acid 30mg/L that is incubated anaerobically at 35-37°C for 5-10 days. Actinomyces may be inhibited by neomycin, hence selective medium with neomycin should be avoided.
There are currently five genera of anaerobic Gram-positive cocci which may be isolated from humans. These include Peptostreptococcus, Peptinophilus, Micromonas, Finegoldia, Anaerococcus. The majority of human isolates are Peptostreptococcus, Peptonphilus and Anaerococcus.
Veillonella species are small asaccharolytic cocci, measuring approximately 0.5 µm in diameter. They are the only Gram-negative anaerobic cocci which are isolated from human clinical material and are rarely found in pure culture. Veillonella species also fluoresce red on exposure to ultraviolet light (365 nm), but this is medium dependent and may fade in a few minutes, on exposure to oxygen. Some species produce catalase.
Many bacteria, including numerous human pathogens, synthesize small molecules known as siderophores to scavenge iron. Enterobactin, a siderophore produced by enteric bacteria, is surprisingly ineffective as an iron-scavenging agent for bacteria growing in animals because of its hydrophobicity and its sequestration by the mammalian protein siderocalin, a component of the innate immune system.
The genus Peptococcus now contains only one species, Peptococcus niger. Typically, cells are 0.3 to 1.3 µm in diameter arranged singly, in pairs or clumps and it grows very slowly. Black pigment is produced after five days incubation but is lost on subculture.
Aerobactin (bacterial siderophore) production can be demonstrated by a cross-feeding bioassay that uses Escherichia coli strain LG 1522. The clinical isolates are grown overnight in M9 broth containing the iron chelator 2-2' dipyridyl. Strains are spotted onto hardened dipyridyl minimal agar plates. After 18 hours incubation at 37°C, satellite growth of the indicator strain LG 1522 around the spots indicates aerobactin production.
Rhinoscleroma is a chronic granulomatous condition of the nose and other structures of the upper respiratory tract. Rhinoscleroma is a result of infection by the bacterium Klebsiella rhinoscleromatis. The Polish surgeon Johann von Mikulich in Wroclaw described the histologic features in 1877; von Frisch identified the organism in 1882.
Phylogenetic analyses of E. coli have shown that isolates can be divided into four main phylogenetic groups, namely A, B1, B2 and D. Virulent isolates causing extraintestinal infections belong mainly to group B2 and, to a lesser extent, to group D, whereas most commensal strains belong to groups A and B1.

Mycology

10% KOH may be preserved with 0.1% thimerosal or its digestive capabilities may be enhanced by 40% dimethyl sulfoxide. A small amount of lactophenol cotton blue or Quink black ink can be added to 10%KOH mount for enhanced visibility of fungal elements.
Sabouraud's agar for dermatophytes contain 0.5µg/ml cycloheximide and 16 µg/ml of chloramphenicol.
The hyphae of Aspergillus sps are not as broad or irregular in diameter as those of zygomycetes. Aspergillus hypha are septate and tend to branch dichotomously at approximately 45 o angles.
If zygomycetes infection is suspected, the tissue must be minced and not ground to avoid destruction of aseptate hyphae.
Commonly used antibiotics to inhibit bacterial contaminants are: Streptomycin + Penicillin and Gentamicin + Chloramphenicol. The advantage of the second combination is that the medium can be autoclaved after adding the antibiotics.
Fungi require a relative humidity of 40-50% in the incubator. This may be achieved by using humidified incubator or by placing a pan of water.
Fungal colony appear smooth or glabrous if the thallus is composed exclusively of vegetative hyphae. Fungi that sporulate heavily have granular colony.
Fungal colonies often develop irregular folds called rugae, which probably represents varying growth rates at different times of development. Rugae often eminate radially from the center of the colony or they may appear as concentric circular rings.
Entire granular colony with a raised center umbonation often are the initial indication that a colony may be turning sterile and should be avoided when subcultured to other media.
The term conidia is taken from Greek, meaning dust. The name Aspergillus is derived from an instrument, such as a brush or a perforated container, used for sprinkling holy water.
Conidia forming in clumps are said to be derived acropetally. E.g. Cephalosporium. Spores that are quire small and singly attached to the hyphal strands via delicate connecting cells are termed microaleurispores (formerly microconidia).
Melanin has been reported in several human pathogenic dimorphic fungi including Paracoccidioides brasiliensis, Sporothrix schenckii, Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides posadasii. Melanization appears to contribute to virulence by reducing the susceptibility of melanized fungi to host defense mechanisms and antifungal drugs.
Factors that favour Candidiasis are young age, pregnancy, corticosteroid/steroid therapy, onset of puberty, extremes in diet, drugs, prolonged administration of antibiotics, general debility and the constitutionally inadequate patient, avitaminosis, diabetes, cancer and its therapy, AIDS, neutropeniaiatrogenic and barrier break procedures, e.g. catheters,dialysis, surgery, injections, wounds, burns, etc.
Dimorphic fungi are converted to species specific phase when incubated in appropriate medium and incubated at 37oC producing small oval budding yeast with narrow attachment for Histoplasma capsulatum, large thick walled budding yeast with broad base for Blastomyces dermatitidis, round or variable yeast and cigar shaped bodies for Sporothrix schenckii , yeast-like structure, bisected cells, arthroconidia for Penicillium marneffei, large thick-walled multiple buddings, narrow connection like marine wheel for Paracoccidioides brasiliensis and spherule production in converse medium incubated at 45oC corresponds to Coccidioides immitis.
In the past, the only way to identify the dimorphic fungi was to convert from one form to the other, but now it is possible to take the mycelial growth (which is the easiest to grow), and confirm the isolate with a DNA probe in a matter of hours.
Bromocresol purple-milk solids-glucose medium (BCPS-G) was first devised by Fischer and Kane for use in identification and purification of dermatophyte isolate. The bromocresol purple indicator was added in part to permit the detection of bacterial contaminants in culture. Typical cultures of Trichophyton mentagrophytes produce spreading growth and a pronounced alkaline pH change at 7 days, while Trichophyton rubrum typically showed a restricted pattern of growth and produced no pH changes within the same period.
The anthropophilic dermatophytes are primarily parasitic on man. They are unable to colonise other animals and they have no other environmental sources. On the other hand, geophilic species normally inhabit the soil where they are believed to decompose keratinaceous debris.Some species may cause infections in animals and man following contact with soil. Zoophilic species are primarily parasitic on animals and infections may be transmitted to humans following contact with the animal host. Zoophilic infections usually elicit a strong host response and on the skin where contact with the infective animal has occurred ie arms, legs, body or face.
It is important to recognise that the toe web spaces are the major reservoir on the human body for these fungi and therefore it is not practical to treat infections at other sites without concomitant treatment of the toe web spaces. This is essential if a "cure" is to be achieved. It should also be recognised that individuals with chronic or subclinical toe web infections are carriers and represent a public health risk to the general population, in that they are constantly shedding infectious skin scales.
Ectothrix invasion is characterised by the development of arthroconidia on the outside of the hair shaft. The cuticle of the hair is destroyed and infected hairs usually fluoresce a bright greenish yellow colour under Wood's ultraviolet light. Common agents include M. canis, M. gypseum, T. equinum and T. verrucosum. Endothrix hair invasion is characterised by the development of arthroconidia within the hair shaft only. The cuticle of the hair remains intact and infected hairs do not fluoresce under Wood's ultraviolet light. All endothrix producing agents are anthropophilic eg T. tonsurans and T. violaceum. Favus usually caused by T. schoenleinii, produces favus-like crusts or scutula and corresponding hair loss.
Staib agar has been widely used for isolation and identification of yeasts from the genus Cryptococcus. It was developed in 1962, by the German mycologist Friedrich Staib, who used Guizotia abyssinica seeds. These seeds contain cafeinic acid, among other phenolic compounds, in which o-diphenol undergoes an oxidation process by the action of phenoloxidase enzyme produced by C. neoformans, resulting in production of a melanin pigment that covers the yeast wall, thus turning the colonies growing on the medium to a dark brown colour.
C. neoformans was originally contained two varieties: var. neoformans (serotypes A, D, and the AD hybrid) and var. gattii (serotypes B and C). More recently, C. neoformans var. gattii has been recognized to be a separate species, Cryptococcus gattii. Molecular studies and genome sequences have detected significant genetic variations between serotypes A and D, and recently serotype A has been distinguished as a new variety, var. grubii. Currently, this organism is classified into two varieties and a sibling species: C. neoformans var. neoformans (D), C. neoformans var. grubii (A), and C. gattii (B, C).
Creatinine dextrose bromothymol blue thymine (CDBT) is the medium of choice for the differentiation of Cryptococcus neoformans var. neoformans and Cryptococcus neformans var. grubii. Cryptococcus neoformans var. neoformans grows as bright red colonies, turning the medium a bright orange after 5 days.
Canavanine-glycine-bromothymol blue (CGB) medium is used to identify Cryptococcus isolates. When inoculated in this medium and incubated at room temperature for 5 days C. neoformans var neoformans forms yellow coloured colonies whereas C. neoformans var gattii forms dark blue colonies.
Zygomycosis caused by Conidiobolus sp. is a chronic inflammatory or granulomatous disease that is typically restricted to the nasal submucosa and characterised by polyps or palpable restricted subcutaneous masses. Human infections occur mainly in adults with a predominance in males. Most cases have been reported from the tropical rain forest areas of central and west and south and central America. Infections usually begin with unilateral involvement of the nasal mucosa.
The genus Cladophialophora includes Cladophialophora carrioinii, Cladophialophora bantiana, Cladophialophora boppii, Cladophialophora arxii and Cladophialophora devriesii. Cladophialophora spp are the causative agents of phaeohyphomycosis, chromoblastomycosis and mycetoma. C. bantiana is neurotropic and causes cerebral phaehyphomycosis in the form of brain abscess. C. boppii and C. carrioinii are isolated from chromoblastomycosis. C. devriesii has been reported to cause disseminated phaehyphomycosis.
The term chromoblastomycosis is restricted to the cases in which sclerotic cells are present in tissue. Sclerotic cells, also known as Medlar bodies, are globe-shaped, cigar-colored, thick-walled structures that are 4-12 µm in diameter. Medlar first described them in 1915. These structures multiply by septation, and they induce a purulent and granulomatous inflammatory reaction in tissue.
Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate] has been used as a fungicide for over 20 years. It became known as a taxonomically selective fungicide when Bollen and Fuchs and Edgington et al. demonstrated that it inhibited most ascomycetous fungi but caused slight or no inhibition for most basidiomycetous and zygomycetous fungi. Since then it has been used in numerous selective media for the division Basidiomycota, the division Zygomycota, and members of the resistant genus Alternaria.
Amanita phalloides poisoning is mediated by a number of toxins, the most important of which are the amatoxins. These toxins interfere with DNA transcription by inhibiting RNA polymerase B. Synthesis of messenger RNA and subsequent protein synthesis is interrupted. Cells with high rates of protein synthesis (e.g. those of the gastrointestinal tract, the liver and the kidneys) are particularly sensitive to injury. young mushrooms. Severe poisoning can occur with 5-7 mg amatoxin, an amount that can be present in a single mushroom weighing about 50 g.
A 90-min test for N-acetyl-,B-galactosaminase coupled with a test for prolyl aminopeptidase has been shown to be as accurate as the germ tube test for Candida albicans.
Candida glabrata is often the second or third most common cause of candidiasis after C. albicans. C. glabrata infections can be mucosal or systemic and are common in abnormal hosts (e.g., immunocompromised persons or those with diabetes mellitus). C. glabrata infections are difficult to treat and are often resistant to many azole antifungal agents, especially fluconazole. C. glabrata is the only Candida species that does not form pseudohyphae at temperatures above 37°C.
The genus Absidia currently contains 21 species. Absidia spp. are filamentous fungi that are cosmopolitan and ubiquitous in nature as common environmental contaminants. They are found in plant debris and soil, as well as being isolated from foods and indoor air environment. The most commonly isolated species is Absidia corymbifera. It is the only recognized pathogen among the other Absidia species.
There are three main species of Acremonium implicated in infections: Acremonium falciforme, Acremonium kiliense, and Acremonium recifei. Acremonium is one of the causative agents of eumycotic white grain mycetoma. Rare cases of onychomycosis, keratitis, endophthalmitis, endocarditis, meningitis, peritonitis, and osteomyelitis due to Acremonium have also been reported. This fungus is known to cause opportunistic infections in immunocompromised patients, such as bone marrow transplant recipients.
The aflatoxins are a group of structurally related toxic compounds produced by certain strains of the fungi Aspergillus flavus and A. parasiticus. The most pronounced contamination has been encountered in tree nuts, peanuts, and other oilseeds, including corn and cottonseed. The major aflatoxins of concern are designated B1, B2, G1, and G2. Aflatoxins produce acute necrosis, cirrhosis, and carcinoma of the liver. LD50 value ranges from 0.5 to 10 mg/kg body weight. Aflatoxin B1 is a very potent carcinogen in many species.
Alternaria is a cosmopolitan dematiaceous (phaeoid) fungus commonly isolated from plants, soil, food, and indoor air environment. The production of melanin-like pigment is one of its major characteristics. Its teleomorphic genera are called Clathrospora and Leptosphaeria. The genus Alternaria currently contains around 50 species. Among these, Alternaria alternata is the most common one isolated from human infections. They have emerged as opportunistic pathogens particularly in patients with immunosuppression, such as the bone marrow transplant patients.
Allylamines antifungal agents [naftifine (topical) or terbinafine (oral)] inhibit cholesterol (mammalian) and ergosterol (fungal) synthesis by interfering with an enzyme necessary for sterol synthesis. The fungal form of squalene epoxidase is more sensitive to these compounds than the mammalian form.
Griseofulvin a compound derived from Penicillium griseofulvum targets microtubule aggregation during nuclear division. Polyoxins and nikkomycins inhibits chitin synthase competitively.
Polyene antimycotics bind to membrane sterols and disrupt their structure/function; increases membrane permeability, leakage of cell contents, and causes cellular death. E.g. Amphotericin B and Nystatin. Azoles - imidazoles and triazoles, acts primarily on ergosterol biosynthesis resulting in (a) ergosterol depletion and (b) accumulation of methylated sterols plasma membrane structure with severely altered function.
For Amphotericin B and 5-Fluorocytosine the zone of inhibition should be determined at the point of complete (100%) or almost complete (95%) inhibition. For the azoles Ketoconazole, Fluconazole and Itraconazole the zone of inhibition should be read at the first point of significant inhibition/marked decrease in growth intensity ie (80%) inhibition. Pinpoint microcolonies at the zone edge or within the zone of inhibition should be ignored.
Chronic mucocutaneous candidiasis (CMC) is the label given to a group of overlapping syndromes that have in common a clinical pattern of persistent, severe, and diffuse cutaneous candidal infections. These infections affect the skin, nails and mucous membranes. Immunologic studies of patients with CMC often reveal defects related to cell-mediated immunity.
Rhizopus species are the most commonly implicated organisms causing zygomycosis in humans. In the family Cunninghamellaceae, only one species, Cunninghamella bertholletiae, has so far been proven to infect humans. The genus Saksenaea contains Saksenaea vasiformis as its only member. Cokeromyces is likewise monotypic. Cokeromyces recurvatus is an unusual clinical isolate which can colonize the human colon and genitourinary tract.
The Entomophthorales are distinguished from the Mucorales by their production of actively expelled asexual sporangioles and by their markedly compact and glabrous mycelial morphology.
Initial designation of the diseases associated with the Zygomycetes reflected the predominance of the Mucorales in causng disease in humans. The term "mucormycosis" was commonly used to describe disease caused by these agents. A subsequent designation of "phycomycosis" was transiently employed to encompass the members of both the orders Mucorales and Entomophthorales. The currently accepted designation is "zygomycosis," reflecting all disease processes caused by the members of the class Zygomycetes.
Molecular studies have determined that there are six species of Trichosporon: T. ashii, T. asteroides, T. cutaneum (synonym of T. beigelii), T. mucoides, T. ovoides and T. inkin. The last two species are also involved in cases of white piedra, while the remaining species are responsible for pneumonitis, mucous infections, endocarditis, keratitis, hepatitis and peritonitis, etc.
Ability of a fungus to grow at 37°C and physiological pH is a virulence factor for fungi that invade deep tissues and the transition to a parasitic form is essential for the pathogenicity of the dimorphic fungi.
Coccidioides immitis spherules are coated with an extracellular matrix which appears to restrict polymorphonuclear leucocyte (PNML) access and may be responsible for the relative resistance of spherules to PMNL-mediated killing.
The capsule of Cryptococcus neoformans is a potent activator of the ternative complement pathway. In cryptococcal sepsis, massive activation of complement by capsular polysaccharide can lead to marked depletion of serum complement components and loss of serum opsonic capacity.
Unfortunately, the most commonly isolated form of T. rubrum is usually nonsporulating. Potato-carrot agar can be used to stimulate conidia formation.
Tricothecene (T-2) mycotoxins are naturally occurring toxins produced by the fusarial species of fungus. T-2 mycotoxins are unique among biotoxins as it is the only known biologically active toxin that can cause disease through dermal, gastrointestinal and inhalational exposure. It is known to cause disease to humans through ingestion of moldy wheat or corn grain.
Tinea imbricata, a dermatophytic infection of man, caused by Trichophyton concentricum, has an ornate appearance composed of concentric circles and polycyclic or serpiginous scaly plaques. The condition is common in several humid tropical regions, especially in parts of Polynesia and Melanesia. The disease was named by Sir Patrick Manson.
Sporotrichosis is a subcutaneous or systemic infection caused by Sporothrix schenckii, a rapidly growing dimorphic fungus. The organism derives its name from R B Schenck, who first reported the infection in 1898. Sporothrix typically exists as a saprophytic mold on vegetative matter in humid climates worldwide. A dimorphic fungus, the organism exhibits mycelial forms at 25°C and a yeast form at 37°C.
The microscopic examination of pus or superficial scrapings from mucosal lesions in South American Blastomycosis reveals thick-walled spherical yeast cells with multiple peripheral buds encircling a mother cell (ie,pilot's wheal or mariner's wheal). This pilot's wheel configuration measures as long as 60 µm in diameter and is highly characteristic of P brasiliensis.
In order to accurately identify many fungi it is essential to observe the precise arrangement of the conidiophores and the way in which spores are produced. Riddel's simple method of slide culturing (described in 1950) permits fungi to be studied virtually in situ with as little disturbance as possible.
Periodic acid-Schiff staining of sporotrichosis lesion reveals the round to oval, cigar-shaped spores within the granuloma. The rare extracellular asteroid bodies of eosinophilic spicules surrounding a central yeast are specific for sporotrichosis, as asteroid bodies seen in other granulomatous reactions are intracellular, filamentous myelin figures that contain lipid.
The genus Scedosporium consists of two medically important species: Scedosporium apiospermum (and its teleomorph or sexual state Pseudallescheria boydii) and Scedosporium prolificans (formerly S. inflatum). The range of diseases caused by these fungi is broad, ranging from transient colonization of the respiratory tract to saprophytic involvement of abnormal airways, allergic bronchopulmonary reaction, invasive localized disease, and at times disseminated disease.
Saksenaea vasiformis is a rare human pathogen that has also been associated with invasive lesions following traumatic implantation of the fungus and rhinocerebral, cutaneous and disseminated types of infection have also been reported. S. vasiformis appears to have a world-wide distribution in association with soil. Sporangia are typically flask-shaped with a distinct spherical venter and long-neck, arising singly or in pairs from dichotomously branched, darkly pigmented rhizoids. Columella are prominent and dome-shaped.
The azole drugs including fluconazole target lanosterol 14-alpha-demethylase, the product of the ERG11 gene. Erg11p is one of the enzymes in the biosynthesis of ergosterol, the major sterol of fungal membranes. Antifungal drug resistance in Candida albicans has been associated with point mutations and increased levels of expression of the ERG11 gene.
Drug efflux from the cells is another component of resistance in C. albicans, as overexpression of two types of efflux pump has been correlated with antifungal resistance. The ABC transporter genes CDR1 and CDR2 encode ATP-dependent efflux pumps that are overexpressed in many azole resistant isolates.
Mackenzie stated that the term germ tube " is a misleading one, as the similarity to the true germinative process of fungal spores is both superficial and transient." He proposed the descriptive term "pseudogerm tubes" for these structures characterized by "the production from any part or the surface of the parent cell and absence of proximal constrictions."
Rhizopus oryzae (=R. arrhizus) is the most common causative agent of zygomycosis, accounting for some 60% of the reported culture positive cases, and nearly 90% of the rhinocerebral forms of infection. It is often used in the production of fermented foods and alcoholic beverages in Indonesia, China and Japan. However, it also produces the ergot alkaloid agroclavine which is toxic to humans and animals.
Presence or absence of hyphae or pseudohyphae in C. albican is determined in corn meal agar (without glucose) containing 1% Tween 80 in a petri dish. A small amount of growth on a stiff needle is pressed through the agar to the bottom of the plate and then drawn through the agar at an angle to make a long cut. Incubation is at room temperature for 24 to 48 h. Production of hyphae is observed by inverting the plate on the stage of the microscope and viewing with the low-power (10x) objective lens.
Taplin and coworkers introduced dermatophyte test medium (DTM) to provide a simple and rapid method for medics in Vietnam to isolate and recognize dermatophytes from soldiers with ringworm infections. The medium contains antibacterial (gentamicin sulfate and chlorotetracycline HCl) and antifungal (cycloheximide) antibiotics in a nutrient agar base along with a pH indicator (phenol red). Alkaline conditions associated with growth of dermatophytes convert the color of the medium from straw yellow to bright red.
Rhinosporidium seeberi, has never been successfully propagated in vitro. Initially thought to be a parasite for more than 50 years, R seeberi had been considered a water mold. Molecular biological techniques have recently demonstrated that this organism is an aquatic protistan parasite. It is currently included in a new class, the Mesomycetozoea, along with organisms that cause similar infections in amphibians and fish.
Several nondermatophytic pathogens [Blastomyces dermatitidis, Acremonium (Cephalosporium) falciforme, Histoplasma capsulatum, Scedosporium apiospermum, and Sporothrix schenckii] were found to be readily misidentified as dermatophytes if the identification was based on their colony morphologies and their ability to induce the appropriate color change in the dermatophyte test medium.

Parasitology

Dientamoeba fragilis was first described in 1918 and has been taxonomically placed in the phylum Parabasala, class Trichomonadeae, family Trichomonadideae.
Acanthamoeba is a rare cause of infection that if not diagnosed early can lead to profound ocular inflammation and visual loss. Due to the resistance of Acanthamoeba cysts to the majority of biocidal agents it is one of the most difficult ocular infections to treat.
Acanthamoeba was first described by Castellani when he reported the presence of an ameba in Cryptococcus pararoseus cultures. The genus Acanthamoeba was established later by Volkonsky in 1931. The first suggestion that Acanthamoeba could cause disease in humans came in 1958 during polio vaccine safety trials. Plaques appeared in cell cultures used to prepare vaccine and were thought to be virus induced because mice and monkeys died from encephalitis following inoculation of tissue culture fluid. However, these plaques were found later to be caused by amebae. Both trophozoites and cysts were detected in cell cultures and were identified as belonging to the genus Acanthamoeba.
The presence of IgG and/or IgM Toxoplasma antibodies in a single serum sample drawn during gestation cannot be used to define whether the infection was recently acquired or chronic. Demonstration of seroconversion or a significant rise in IgG Toxoplasma antibodies usually establishes recently acquired infection. The utility of the avidity test is based on the observation that toxoplasma IgG antibodies from patients with a recently acquired T. gondii infection bind antigens weakly (i.e., have low avidity), whereas IgG antibodies from chronically infected patients have stronger binding capacity (high avidity).
Molecular phylogeny places entamoeba on one of the lowermost branches of the eukaryotic tree, closest to dictyostelium. Although the organism was originally thought to lack mitochondria, nuclear-encoded mitochondrial genes and a remnant organelle have now been identified. Unusual features of entamoeba include polyploid chromosomes that vary in length; multiple origins of DNA replication; abundant, repetitive DNA; closely spaced genes that largely lack introns; a novel GAAC element controlling the expression of messenger RNA; and unique endocytic pathways.
E. histolytica evades the host immune response in several ways. The Gal/GalNAc-specific lectin has sequence similarity and antigenic cross-reactivity to CD59, a human leukocyte antigen that prevents the assembly of the complement C5b-C9 membrane attack complex. Amebic cysteine proteinases rapidly degrade the complement anaphylatoxins C3a and C5a. The cysteine proteinases also degrade secretory IgA and serum IgG, possibly protecting amebae from opsonization. Finally, amebae appear to suppress both the macrophage respiratory burst and antigen presentation by class II major-histocompatibility-complex (MHC) molecules.
Giardia duodenalis, also known as Giardia lamblia and Giardia intestinalis, is a flagellated diplomonad and the most commonly detected flagellate and protozoan in the intestinal tract. The trophozoites were first noted by von Leeuwenhoek in 1681 in his own stools.
Trichomonas vaginalis lacks mitochondria and other characteristics of higher eukaryotic respiratory metabolism such as cytochromes and oxidative phosphorylation. Nutrients are taken up by transport through the cell membrane and by phagocytosis. Trichomonas is regarded as an anaerobe.
By binding to free b-tubulin, benzimidazoles (thiabendazole, mebendazole, and albendazole) inhibit the polymerization of tubulin and the microtubule-dependent uptake of glucose. The newest benzimidazole, albendazole, has a broad range of activity against many nematode and cestode parasites.
Ivermectin is an extremely potent, broad-spectrum, anthelmintic drug that has been widely used in controlling nematode infections. It has been used most extensively against onchocerciasis. It is a semisynthetic macrocyclic lactone derived from the soil mold Streptomyces avermitilis. It appears to kill helminths by opening chloride-sensitive channels. Ivermectin may be effective in treating ectoparasitesin humans, including scabies and head lice.
Praziquantel is an effective drug against a broad range of trematode and cestode infections. It appears to interfere with calcium homeostasis and causes flaccid paralysis in adult flukes. Perhaps by disrupting the surface membrane of the parasite, praziquantel causes antigens within the parasite to be exposed to the action of host antibodies.
Fumagillin is a water-insoluble antibiotic produced by Aspergillus fumigatus. Over four decades ago, fumagillin was found to inhibit the activity of intestinal protozoa, including Entamoeba histolytica, the causative agent of amebiasis. Fumagillin had not been used in human infections.
Babesiosis, caused by infection with intraerythrocytic parasites of the genus Babesia, is one of the most common infections of free-living animals worldwide and is gaining increasing interest as an emerging zoonosis in humans. All babesial parasites described to date are transmitted by ixodid ticks to their vertebrate hosts.
Balamuthia, has been discovered to cause a fatal encephalitis in humans. This encephalitis is known as Balamuthia amoebic encephalitis (BAE). At present there is a single species in this novel genus, Balamuthia mandrillaris. Genetic analysis has revealed that Balamuthia is a close relative of Acanthamoeba. Despite this relationship, B.mandrillaris is found to prey on Acanthamoeba.
Baylisascariasis in humans is caused by infection with the nematode parasite Baylisascaris procyonis. Baylisascaris procyonis and related species are large nematodes of the order Ascaridida. In its most severe form, B. procyonis is a rare cause of fatal or neurologically devastating neural larva migrans (NLM) in infants and young children. Characteristically, B. procyonis NLM presents as acute eosinophilic meningoencephalitis.
The common bedbug (Cimex lectularius) is found in temperate climates throughout the world and lives off the blood of humans. Bedbugs are generally active only at dawn, with a peak attack period about an hour before sunrise. They may attempt to feed at other times, however, given the opportunity, and have been observed to feed at any time of the day. Attracted by warmth and the presence of carbon dioxide, the bug pierces the skin of its host with two hollow tubes. With one tube it injects its saliva, which contains anticoagulants and anesthetics, while with the other it withdraws the blood of its host. After feeding for about five minutes, the bug returns to its hiding place.
While assessment of CSF may be of value in the diagnosis of Granulomatous Amebic Encephalitis (GAE), lumbar puncture may be contraindicated because of increased intracranial pressure. CSF is centrifuged at low speed (250 x g) for 10 min to avoid rupture of trophozoites. Trophozoites may be observed in wet preparations of CSF but may be unrecognized because they resemble macrophages. CSF sediment can be smeared on a glass slide, fixed in methanol, and stained with Giemsa-Wright stain. However, certain characteristic features of Acanthamoeba trophozoites such as a prominent nucleolus, contractile vacuole, and cytoplasmic vacuoles may be visualized more readily using trichrome or hematoxylin and eosin stains on fixed preparations after cytocentrifugation rather than using air-dried preparations.
Intestinal amebiasis is most commonly diagnosed by identifying cysts or motile trophozoites on a saline or iodine wet mount of a stool specimen. The drawbacks of this method include its low sensitivity and false positive results owing to the presence of E. dispar or E. moshkovskii infection. The diagnosis should ideally be based on the detection in stool of E. histolytica specific antigen or DNA and by the presence of antiamebic antibodies in serum.
Ticks are blood feeding external parasites of mammals, birds, and reptiles throughout the world. Approximately 850 species have been described worldwide. There are two well established families of ticks, the Ixodidae (hard ticks), and Argasidae (soft ticks). Hard ticks have three distinct life stages. Larvae which emerge from the egg have six legs. After obtaining a blood meal from a vertebrate host, they molt to the nymphal stage and acquire eight legs. Nymphs feed and molt to the next and final stage - the adult, which also has eight legs. After feeding once more, the adult female hard ticks lay one batch of thousands of eggs and then die. Only one blood meal is taken during each of the three life stages.
The life stages of soft ticks are not readily distinguishable. The first life stage to come out of the egg, a six legged larva, takes a blood meal from a host, and molts to the first nymphal stage. Unlike hard ticks, many soft ticks go through multiple nymphal stages, gradually increasing in size until the final molt to the adult stage. Soft ticks feed several times during each life stage, and females lay multiple small batches of eggs between blood meals during their lives.
The microfilaria of B. malayi can be distinguished from those of W. bancrofti by the two isolated nuclei at the tip of the tail and the absence of nuclei in the cephalic spaces.
Identification of Acanthamoeba at the genus level is relatively easy due to the presence of spiny surface projections, termed acanthopodia, on trophozoites. However, using morphological criteria identifi cation of these amebae at the species level has been difficult. Acanthamoeba spp. have been placed into three morphological groups (I, II, and III) based on cyst size and shape.
Although Cryptosporidium parvum is the most common species in humans, C. felis, C. muris, and C. meleagridis have also been identified in immunocompromised persons. Two distinct C. parvum genotypes are known to infect humans: human type 1 and bovine type 2. Cryptosporidium is capable of completing all stages of its development (asexual and sexual) within a single host.
A defining feature of the hemoflagellates and of the order Kinetoplastida is a unique DNA-containing organelle, the kinetoplast, associated with the mitochondrion of the organism. Representatives of the hemoflagellates are pleomorphic, adopting a variety of stages in the course of their life cycles. The stages differ morphologically from one another in shape, location of the kinetoplast, and the extent of the flagellum.
Fedor Aleksandrovich Losch in 1875 was the first to describe the trophozoite form of E. histolytica and the pathology associated with the infection in a patient from St. Petersburg, Russia. Although Losch was able to infect a dog with organisms obtained from the patient, he was not able to mimic the disease produced in humans. Quincke and Roos in 1893 described the cyst form, and Schaudinn in 1903 named E. histolytica and differentiated it from E. coli. Boeck and Drbohlav were the first to successfully cultivate E. histolytica by using Locke's egg serum medium. Other media frequently used to culture pathogenic strains include those described by Robinson, Balamuth, and Jones; however, the first axenic cultivation was accomplished by Diamond.
Trypanosoma brucei brucei was initially grown on Novy-McNeal medium, which was later modified by Nicolle. This medium, referred to as NNN medium consisted of blood agar slants inoculated with infected materials. Parasite growth occurred in the water that had condensed on the agar surface. More recently, a fluid overlay of Locke's solution containing glucose over a nutrient-blood agar base has been employed as a diphasic medium. Embryonated eggs have also been used successfully for the cultivation of trypanosomes.
Acanthamoeba can be grown on Non Nutrient Agar (1.5%) containing a lawn of Escherichia coli. Acanthamoeba also can be grown axenically in PYG medium consisting of 2% proteose peptone, 0.2% yeast extract, and 0.1 M glucose or in Oxoid medium (Cline medium) containing serum and hemin, which has been used to culture Naegleria spp. Mammalian cells which support the growth of Acanthamoeba include African green monkey kidney (Vero),human embryonic lung (HEL), human embryonic kidney (HEK), HeLa, B103 rat neuroblastoma, and L929 fibroblasts.

Virology

Density gradient centrifugation involves centrifuging particles (such as virions) or molecules (such as nucleic acids) in a solution of increasing concentration, and therefore density. The solutes used have high solubility: sucrose is commonly used. There are two major categories of density gradient centrifugation: rate zonal and equilibrium centrifugation.
Acidophilic inclusion bodies of Variola, Vaccinia and Herpes can be stained by Giemsa, Paschen and Gutstein methods.
In 1881, Carlos Finlay proposed the mosquito-borne transmission of Yellow Fever. In 1900, Walter Reed and colleagues observed that the infectious agent, a filterable virus, was transmitted by means of a mosquito bite. YF virus is transmitted to the mosquito from an ill human only during the initial 3-4 days of illness. Approximately 3-10 virions are necessary to infect a mosquito. The extrinsic incubation period (interval from infection of the mosquito with YF virus until the mosquito can transmit YF to another host) is 12-21 days.
The interferon system is the first line of defense against viral infection in mammals. This system is designed to block the spread of virus infection in the body, sometimes at the expense of accelerating the death of the infected cells. They are induced in mammalian cells in response to virus infection, secreted to circulation, and act on as yet uninfected cells to activate a global antiviral state.
Viruses such as certain baculoviruses and adenoviruses are used as vectors to take genes into animal cells growing in culture. This technology (genetic engineering) can be used to insert into cells genes encoding useful proteins, such as vaccine components, and the cells can then be used for mass production of the proteins.
The units in which virions are normally measured are nanometres (1 nm = 10-9 m). Although virions are very small, their dimensions cover a large range. Amongst the smallest are parvoviruses, with diameters about 20 nm, while the microbe-mimicking virus (mimivirus), isolated from an amoeba, is amongst the largest.
Live attenuated virus preparation prepared by culturing 17D strain virus in living chick embryo is available against Yellow fever. Immunity may start 7-10 days after vaccination. Cholera and YF vaccinations reduce response to each other and should be administered at least 3 weeks apart.
Bacteria can be preserved for short durations in brain heart infusion broth with 15% glycerol that are snap frozen in liquid nitrogen and stored at -70o C.
Turning of egg in an incubator is important. This prevents adhesion of membranes and also facilitates dispersal of toxic products arising from embryonic development. It is ideal to turn egss every 4-8 hours.
For inoculation into allantoic cavity, a 9-12 day old embryonated egg is chosen. A quantity of 0.05 ml is inoculated using a 26swg x ½ inch needle. For inoculation into amniotic cavity, a 7-15 day old egg is chosen. A volume of 0.1-0.2 ml is inoculated using 26swg x 1 inch needle.
Flury strain, isolated in 1939 from a fatal case of Rabies in a girl has diminished pathogenicity without loss of antigenicity for dog.
Negri bodies, named after Dr. Adelchi Negri are eosinophilic cytoplasmic inclusion bodies of Rabies virus that measure 3-4µm and is found in nerve cells particularly of hippocampus. In humans, medulla and thalamus are the best source of virus. Seller's stain can be used to visualise them in impression smears. Mann's method (eosin methylene blue) and Giemsa stain can also be used to stain Negri bodies.
Influenza A and B virus may or may not agglutinate fowl RBCs on primary isolation, they should be tested against human or guinea pig RBC at toom temperature. Influenza C virus will only agglutinate fowl RBC at 4oC.
The first licensed rotavirus vaccine, Rotashield, was an attenuated combination of rhesus monkey and human strains of the virus. Following efficacy and cost-efficacy trials it was introduced as a routine immunisation in the US. Post-marketing surveillance revealed an increased incidence of intussusception in the days following a dose of vaccine. Rotashield was withdrawn by the manufacturer in October 1999.
The word prion is an acronym for proteinaceous infectious particle only. PrPC is a membrane protein expressed in most tissues, but more prominently so in brain and neural tissue, and it is encoded from the PrP gene. Ordinary membrane proteins are referred to as PrPC, and the isoform that infects these proteins is called PrPSc. PrPSc proteins infect normal PrPC proteins and alter their composition. PrPC is made up mostly of alpha helix structures, and has almost no beta pleats.
Sabin polio vaccine is composed of three viral types. Type 1 contains 57 mutations and has seldom reverted to wild type, while the Type 2 and 3 vaccines depend for their safety on only two key mutations. In these latter types frequent reversions to wild-type have occurred, some of which have led to outbreaks of paralytic poliomyelitis.
Nipah virus, a new paramyxovirus virus was first recognized in a large human outbreak that affected 283 persons and caused 109 deaths in Malaysia in 1999. Contact with sick pigs was the primary risk factor for human Nipah virus infection. It is most closely related to the recently discovered Hendra virus.
Hepatitis G (HGV) is a flavivirus, which shares about 27 - 40% sequence homology with HCV. HGV is identical to the "GB-C" agent, originally found in a surgeon with hepatitis and later identified in animals to be different from hepatitis viruses A, B, C, D and E, respectively.
The highly pathogenic avian influenza (HPAI) H5N1 virus transmits zoonotically from infected poultry to humans. Two subtypes of influenza A virus (H5 and H7) are known to give rise to HPAI virus in terrestrial poultry (chicken and turkeys).
Bacteriophages were observed by Twort and d'Herelle in 1915 and 1917. They observed that broth cultures of certain intestinal bacteria could be dissolved by addition of a bacteria-free filtrate obtained from sewage. The name "phage" for short is derived from Greek "phagein" meaning "to eat" or "to nibble".
Examples of well-known cell types that are standard for most virology laboratories are primary rhesus monkey kidney (RhMK) cells, primary rabbit kidney cells, human lung fibroblasts (MRC-5), human foreskin fibroblasts, human epidermoid carcinoma cells (HEp-2), and human lung carcinoma cells (A549).
Hepatitis delta virus (HDV) was discovered in 1977 by Rizzetto and colleagues while they were studying liver biopsies of patients with hepatitis B surface antigen (HBsAg)-positive chronic liver disease.
Ebola virus was first recognized near the Ebola River valley during an outbreak in Zaire in 1976. The natural host for Ebola virus is unknown, so it has not been possible to implement programs to control or eliminate viral reservoirs of transmission to human populations.
Epstein-Barr virus (EBV) was discovered by electron microscopy of cells cultured from Burkitt's lymphoma tissue by Epstein, Achong, and Barr. Four years later, in 1968, EBV was shown to be the etiologic agent of heterophile-positive infectious mononucleosis.
An immunodiffusion precipitin line between the HBsAg present in the serum of an Australian Aborigine and the antibody to HBsAg in a patient with hemophilia who had received multiple transfusions provided the first clue. The subsequent development of acute hepatitis in a laboratory technician provided the essential link to the clinical illness. For these achievements, Dr. Baruch Blumberg received the Nobel Prize in Physiology or Medicine in 1976.
CDC has recommended that a person be considered to have serologic evidence of HCV infection only after an anti-HCV screening-test-positive result has been verified by a more specific serologic test (e.g.,the recombinant immunoblot assay) or a nucleic acid test.
HHV-6 exists as two closely related variants, HHV-6A and HHV-6B. HHV-6A has not been etiologically linked to any disease; HHV-6B is the causative agent of exanthema subitum , a childhood disease characterized by high fever and a mild skin rash, occasionally complicated by seizures or encephalitis.
Kaposi sarcoma-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8) is a gamma 2 herpes-virus, identified from the Kaposi sarcoma of an AIDS patient by Chang et al. It has been shown to be directly associated with multicentric Castleman disease (MCD), primary effusion lymphoma (PEL) and solid/extracavitary lymphomas.
HPVs are a very heterogeneous group of viruses Almost 90 HPV types have been described by DNA sequence analysis, with each type defined as having more than 10% dissimilarity in the combined nucleotide sequences of E6, E7, and L1 genes.
The only exception that did not have a confirmed rodent association among the genus Hantavirus has been Thottapalayam virus (TPMV), which was isolated from an Asian house shrew or musk shrew (Sunus murinus) captured in 1964 during a survey for Japanese encephalitis virus in southern India.
The word virus is derived from the Latin for 'poison' and was traditionally used for the cause of any transmissible disease. With the discovery of agents that could pass bacteria-retaining filters, the term 'filterable virus' was introduced and this was later shortened to 'virus'.
Poliovirus was first isolated in 1908 by Landsteiner and Popper, who transmitted the infectious agent to monkeys by injection of a homogenate of the spinal cord from an acutely fatal human case.
Herpes simplex virus (HSV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), mumps, measles, and enteroviruses are responsible for most cases of acute viral encephalitis among immunocompetent individuals. Viruses which infect the central nervous system (CNS) can selectively involve the spinal cord (myelitis), the brain stem (e.g., rhombencephalitis), the cerebellum (cerebellitis), or the cerebrum (encephalitis). In contrast to aseptic viral meningitis, neuropsychiatric symptoms often predominate in encephalitis.
The cerebrospinal fluid (CSF) is abnormal in more than 90% of CNS viral infections, typically consisting of a lymphocytic pleocytosis, mildly elevated protein, and normal glucose. In rare instances, such as West Nile virus (WNV) meningoencephalitis or cytomegalovirus (CMV) radiculomyelitis, polymorphonuclear cells rather than lymphocytes may be the predominant cell type.
Noroviruses that infect human beings were previously called Norwalk-like viruses (NLV) or small round-structured viruses. Norovirus was first discovered in 1972 from faecal specimens collected during an outbreak of gastroenteritis in 1968 in Norwalk, Ohio. Noroviruses infect people of all ages, a feature that distinguishes them from other agents of acute viral gastroenteritis, which primarily affect children.
Promotion of immune complex formation, ability to elicit autoantibodies with reactivity to platelets and extracellular matrix, and damage inflicted on endothelial cells are some of the mechanisms proposed to explain pathogenesis mediated by Dengue virus NS1 protein. The ability of DENV NS1 to bind host complement also point to a role for this protein in DENV pathogenesis.
Live attenuated varicella vaccine was approved by the FDA (USA) in 1995 for administration to healthy susceptible persons 12 or more months of age. A single dose of the vaccine for children 12 or less years of age (ideally administered at 12-15 months of age) and 2 doses of the vaccine administered at least 1month apart for persons 13 or more years of age were recommended.
The Oka strain of live attenuated varicella vaccine originated from a virus isolated from the vesicular fluid of a three-year-old boy (whose family name was Oka) with chicken pox but who was otherwise healthy. The virus was propagated serially for 11 passages at 34°C in human embryonic lung cells (HELF), 12 passages in guinea pig fibroblast cells (GPFC), and 7-8 additional passages in human diploid cells (WI-38 and MRC-5).
In 1997, Nishizawa et al identified a novel virus in the serum of a patient with acute post-transfusion hepatitis of non A-G aetiology. This agent was designated as 'TT' virus (TTV), after the initials of the patient in whom it was discovered. It is a negative sense, single-stranded, non-enveloped DNA virus. This acronym might also stand for transfusion-transmitted virus. It is proposed that the full name for TTV be Torque Teno Virus, within the genus Anellovirus.
Transmissible spongiform encephalopathies (TSEs) are a group of rapidly progressive, invariably fatal, neurodegenerative diseases that affect both humans and animals. Most TSEs are characterized by a long incubation period and a neuropathologic feature ofmultifocal spongiformchanges, astrogliosis, neuronal loss, and absence of inflammatory reaction. TSEs in humans include Creutzfeldt-Jakobdisease (CJD), kuru, Gerstmann-Straussler-Scheinker syndrome (GSS), fatal familial insomnia (FFI), and newvariantCJD(nvCJD).
In 1885 Wilhelm Roux removed a portion of the medullary plate of an embryonic chicken and maintained it in a warm saline solution for several days, establishing the basic principle of tissue culture. In modern usage, "tissue culture" generally refers to the growth of eukaryotic cells in vitro. It is often used interchangeably with cell culture to specifically describe the in vitro culturing of mammalian cells. However, "tissue culture" can also be used to refer to the culturing of tissue pieces, i.e. explant culture or whole organs, i.e. organ culture.
The last case of endemic smallpox occurred in Somalia in 1977, and eradication of the disease was declared in 1980. With no natural reservoir, variola virus has existed only in laboratories. The last case of smallpox was due to infection acquired in a laboratory in the United Kingdom in 1978. By 1984, only the Centers for Disease Control and Prevention (CDC), in Atlanta, and the Research Institute of Viral Preparations, in Moscow, retained variola virus isolates.
Transposable elements are discrete segments of DNA capable of moving from one locus to another in their host genome or between different genomes. They are distributed across the living world. They induce various types of genome rearrangement and are a major source of mutation. In the case of prokaryotic organisms, they are implicated in the acquisition of "accessory" functions such as resistance to antibacterial agents, catabolism of "unusual" substances, virulence, and in the control of expression of neighboring host genes.
Slow virus diseases may be caused by conventional viruses or by the unconventional viruses (actually prions). Progressive multifocal leukoencephalopathy (PML) is a rare, progressive, fatal, demyelinating disease of the CNS (kills oligodendrocytes). It is caused by a member of the papovavirus family, JC virus. Subacute sclerosing panencephalitis (SSPE) is a rare complication of measles virus infection which, develops ~1-10 years after initial infection. Progressive rubella panencephalitis (PRP) is a very rare consequence of rubella virus infection.
Severe acute respiratory syndrome (SARS) is a serious, potentially life-threatening viral infection caused by a virus from the Coronaviridae family. This virus has been named the SARS-associated coronavirus (SARS-CoV). It is believed to have originated in Guangdong province in southern China in November 2002. Isolation of the virus from respiratory secretions, feces, urine, and tissue specimens from lung biopsy, indicates that the infection is not confined to the respiratory tract.
The serological diagnosis of Rubella infection is based on the presence of specific IgG and IgM antibodies. More recently, assays of the avidity of IgG (i.e. the strength of IgG binding to a multivalent antigen of the virus), have been used to distinguish recent from old infections in individuals with high IgG levels. At the onset of the immune response in acute phase, the IgG generated by the antigenic stimulus has low avidity, but as time goes by in the convalescence, after the first two to four months of infection, avidity increases.
Acyclovir is an analogue of 2'-deoxyguanosine that exerts its antiviral effect after being metabolized to acyclovir triphosphate. Acyclovir triphosphate inhibits the synthesis of viral DNA by competing with 2'-deoxy-guanosine triphosphate as a substrate for viral DNA polymerase. Once acyclovir is inserted into the replicating viral DNA, synthesis stops. The incorporation of acyclovir monophosphate into viral DNA is irreversible.
Borna disease virus (BDV) has been linked specifically with dysfunctioning of evolutionarily old brain structures. Unlike the closely related rabies virus, which afflicts limbic structures of the brain and usually destroys them, BDV is noncytolytic, with many specific properties eliciting functional disturbances in the brain resembling those in mood disorders. BDV infection in humans was first detected by serologicalv methods, mainly immunofluorescence assays.
Rubella was once popularly known as German measles. The disease was renamed rubella (from the Latin for reddish things) in 1866 by Henry Veale, a British Army surgeon, who found the original term "harsh and foreign to our ears". In 1941 Norman Gregg, an Australian ophthalmic surgeon, reported the devastating teratogenic effects of the virus.
Incubation of tube cell cultures in rotating or rolling racks has been shown to enhance viral replication. Tube cultures rolled at 2 rpm have a 2.4-fold increase in HSV foci over stationary tube cultures, and those rolled at 96 rpm have a 6.8-fold increase in foci over stationary tube cultures.
The first outbreak of chikungunya was reported from the Makonde Plateau, along the border between Tanzania and Mozambique, during 1952-1953. The term Chikungunya is derived from the Makonde root verb kungunyala, meaning "that which bends up" in reference to the stooped posture developed due to the excruciating joint and muscle pain and other rheumatologic manifestations.
Foscarnet (trisodium phosphonoformate) is an organic analogue of inorganic pyrophosphate. It forms complexes with viral DNA polymerase at its pyrophosphate-binding site, preventing cleavage of pyrophosphate from nucleoside triphosphates and thus blocking further primer-template extension.
Rotavirus is shed in high concentration in the stool of children with gastroenteritis (i.e., 1012 viruses/g), so the most widely available method is antigen detection in the stool by an enzyme immunoassay (EIA) directed at an antigen common to all group A rotaviruses. Latex agglutination and polyacrylamide gel electrophoresis might be less sensitive than EIA but are used in some settings. Other techniques, including electron microscopy, reverse transcription-polymerase chain reaction, nucleic acid hybridization, sequence analysis, and culture, are used primarily in research settings.
In 1966, Parkman et al. developed the first live attenuated vaccine, HPV-77, by passaging RV 77 times in African green monkey kidney cells. In 1969, following passaging of HPV-77 in duck embryo fibroblasts at Merck, HPV-77 DE-5 became the first rubella vaccine licensed for use in the United States. Soon afterward, other live attenuated RV vaccines became available, and one of these, the RA27/3 strain, became the mainstay of vaccination programs in most developed countries.
Examples of phages that carry key virulence factors are phages gamma (Corynebacterium diphtheriae toxin), C1 (Clostridium botulinum toxin) and CTXØ (Vibrio cholera toxin).
Kuru was the first human spongiform encephalopathy shown to be transmissible. This subacute, uniformly fatal disease of cerebellar degeneration reached epidemic proportions among the Fore ethnic group in a remote mountainous area of New Guinea. The disease was spread by ritual cannibalism and has gradually disappeared over the 40 years since the practice ceased.
RotaTeq® is a live, oral vaccine that contains five reassortant rotaviruses developed from human and bovine parent rotavirus strains. Four reassortant rotaviruses express one of the outer capsid proteins (G1, G2, G3, or G4) from the human rotavirus parent strain and the attachment protein (P7[5]) from the bovine rotavirus parent strain. The fifth reassortant virus expresses the attachment protein (P1A[8]) from the human rotavirus parent strain and the outer capsid protein G6 from the bovine rotavirus parent strain. The parent bovine rotavirus strain Wistar Calf 3 (WC3) was isolated from a calf with diarrhea in Chester County, Pennsylvania, in 1981 and was passaged 12 times in African green monkey kidney cells. The reassortants are propagated in Vero cells using standard tissue culture.
Crimean haemorrhagic fever was first described as a clinical entity in 1944-45, when about 200 Soviet military personnel were infected while assisting peasants in Crimea in the wake of World War 2. The virus was isolated from blood and tissues of patients using intracerebral inoculation of newborn white mice in 1967. The virus responsible for Crimean haemorrhagic fever was later shown to be antigenically indistinguishable from Congo virus, isolated in 1956 from a febrile patient in Democratic Republic of the Congo. The virus belongs to the genus Nairovirus in the Bunyaviridae family and causes severe diseases in human beings.
HIV infection of the nervous system is unique when compared with other viral encephalitides. Neuronal cell loss occurs in the absence of neuronal infection. Viral proteins, termed "virotoxins," are released from the infected glial cells that initiate a cascade of positive feedback loops by activating uninfected microglial cells and astrocytes. These activated cells release a variety of toxic substances that result in neuronal dysfunction and cell loss.
In 1974, Cossart et al. first identified B19 while evaluating tests for hepatitis B virus surface antigen. The name originates from the coding of a serum sample, number 19 in panel B, that gave anomalous results when tested by counterimmunoelectrophoresis and radioimmunoassay. Electron microscopy (EM) revealed the presence of 23-nm-diameter particles resembling animal parvoviruses. Since replication only occurs in erythrocyte precursors, B19 is now classified as a member of the Erythrovirus genus, of which it is the only accepted member and type species.
Two echoviruses have distinct biological and molecular properties. These, echoviruses 22 (Harris strain) and 23 (Williamson strain), have recently been assigned to a sixth picornavirus genus, Parechovirus, and have been renamed human parechovirus 1 and 2 (HPEV1 and HPEV2), respectively.
Ribavirin is a guanosine analogue that has an incomplete purine ring rather than an acyclic ribose moiety. After intracellular phosphorylation, ribavirin triphosphate interferes with early events in viral transcription, such as the capping and elongation of messenger RNA, and inhibits ribonucleoprotein synthesis.
An attenuated nasal vaccine for influenza contains cold-adapted vaccine strains of the influenza virus that have been grown in tissue culture at progressively lower temperatures. After a dozen or more of these passages, the virus grows well only at around 25° and in vivo growth is restricted to the upper respiratory tract. The cold-sensitive mutant can be reassorted with any new virulent influenza strain that appears. The reassorted virus will have the genes for the internal proteins from the attenuated virus (and hence will be attenuated) but will display the surface proteins of the new virulent antigenic variant.

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