practical exercises

Illustrations of culture media and related items

  • Agar fibresObtained from certain seaweeds (Gelidium sps). Contain agarose and agaropectin. New Zealand and Japanese agars are popular
  • Agar powderMade from agar fibres. Used at concentration of 0.5% to 2% in culture media as solidifying agent. Does not get hydrolysed by bacterial enzymes and doesn't provide any nutrition. Melts at 95°C and solidifies at 45°C
  • Nutrient broth and nutrient agarNutrient broth and nutrient agar are simple media. They are used to grow non-fastidious bacteria. Glucose broth is especially useful in growing certain gram positive bacteria.
  • Blood agarAn enriched medium prepared by adding 5% sheep blood to basal medium. Used to grow fastidious bacteria and to observe hemolysis.
  • Blood agar with BHSBlood agar with beta hemolytic Streptococci showing areas of complete hemolysis around colonies.
  • Chocolate agarAn enriched medium prepared from lysing sheep blood. Used for recovering fastidious bacteria. Especially useful in recovering Hemophilus and Neisseria.
  • Potassium tellurite agarA selective medium used to recover Corynebacterium diphtheriae from specimens. It is chocolate agar with 0.04% potassium tellurite. Colonies are black because tellurite is reduced to metallic tellurium and incorporated into colonies.
  • Nutrient agarNutrient agar plate: It is a basal medium that is used to recover many non-fastidious bacteria. Used to study colony morphology, pigmentation and for slide agglutination test.
  • Nutrient agar with StaphylococciThree 'species' of Staphylococcus on nutrient agar plate with their pigments. S. aureus is golden yellow, S. citreus is lemon yellow where S.albus is non-pigmented.
  • Antibiotic susceptibility testAntibiotic susceptibility testing by disk diffusion. Mueller Hinton agar is used to grow bacteria. Filter paper disks of known antibiotic concentration is placed on the surface and incubated. Bacteria inhibited by bacteria form zone of inhibition around the antibiotic disk.
  • Glucose broth and bile brothGlucose broth and bile broth are blood culture media. Bile broth is useful in recovering Salmonella in suspected enteric fever cases. Robertson cooked meat medium is used to grow anaerobic bacteria.
  • Enrichment mediaThioglycollate medium is used for growing anaerobic bacteria. Selenite F broth and tetrathionate broth are enrichment media that are used to recover Shigella and Salmonella respectively from fecal specimens.
  • MacConkey's agarAn indicator and differential medium used mainly for growth and identification of Enterobacteriaceae members. Contains lactose, bile salt, peptone, neutral red and agar.
  • MacConkey's agar withLFMacConkey's agar with lactose fermenting colonies. Acid produced by lactose fermenters results in change in colour of colonies to bright pink. E. coli and K. pneumoniae are lactose fermenters.
  • MacConkey's agar with NLFMacConkey's agar with non-lactose fermenting colonies. Since lactose is not fermented, there is no change in the colour of colonies. Salmonella, Shigella and Proteus are non-lactose fermenters.
  • Wilson & Blair's agar with growthWilson & Blair's bismuth sulphite medium with growth. Salmonella grows in presence of brilliant green and bismuth salts. Black colonies are formed when H2S produced by bacteria reduce ferrous sulphate to ferric sulphite. Metallic bismuth provides sheen around the colonies.
  • Wilson & Blair's agarWilson & Blair's bismuth sulphite medium: A selective medium used to isolate Salmonella sps from feces of patients with suspected enteric fever. Brilliant green and bismuth sulphite are used to make it selective.
  • jquery carousel sliderLoeffler's serum slope is serum based and Lowenstein Jensen medium is egg based medium. They are sterilised by inspissation. Loeffler's serum slope is an enriched medium used to grow Corynebacterium diphtheriae. LJ medium is a selective medium that is used to isolate M.tuberculosis.
  • citrate_ureaChristensen's urea agar is used to demonstrate urease activity. When urea is split to ammonia, pH rises resulting in colour change from yellow to pink. Simmon's citrate is used to demonstrate organism's ability to utilize citrate as a sole source of carbon and energy. Alkalinity resulting from this process changes colour of the medium from green to blue.
Agar fibres1 Agar powder2 Nutrient broth and nutrient agar3 Blood agar4 Blood agar with BHS5 Chocolate agar6 Potassium tellurite agar7 Nutrient agar8 Nutrient agar with Staphylococci9 Antibiotic susceptibility test10 Glucose broth and bile broth11 Enrichment media12 MacConkey's agar13 MacConkey's agar withLF14 MacConkey's agar with NLF15 Wilson & Blair's agar with growth16 Wilson & Blair's agar17 Loeffler's serum & LJ medium18 citrate_urea19
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