FAQ in sterilization and disinfection techniques

What is sterilization and disinfection?

The process of killing all living forms including spores is called sterilization and the process of killing of only the vegetative form of pathogenic bacteria as well as other microbes is disinfection.


What is the temperature and time employed to sterilize the articles in hot air oven?

160°C for 60 minutes.


What are the conditions of sterilization in an autoclave?

121°C for 15 minutes at 15 pounds per square inch of pressure.


What are the articles sterilized in a hot air oven?

Glassware’s, metallic instruments like scissors and forceps, swabs, powder, oils and grease.


What are the articles sterilized in an autoclave?

Culture media, gloves, cotton and clothes.


How are heat labile fluids such as serum and antibiotic solutions sterilized?

By filtration.


How is air sterilized?

By High Efficiency Particulate Air (HEPA) filters.


Name some disinfectants?

Phenol, Lysol, Formaldehyde, Sodium hypochlorite.


What are antiseptics?

Antiseptics are mild disinfectants that can be safely used on skin and mucous membranes.


Quaternary ammonium compounds?

Quaternary ammonium compounds are positively charged polyatomic ions, which concentrate at the cell surface and alter the physical and chemical properties of the membrane, thus killing the cell. Examples inlcude Benzalkonium chloride and Cetrimonium bromide.


What do popular brands of antiseptics such as Dettol or Savlon contain?

The active ingredient of Dettol is chloroxylenol whereas Savlon contains a combination of Cetrimide and Chlorhexidine.


Which are the active ingredients of commercial mouthwashes?

The active ingredients include Chlorhexidine, Triclosan, Thymol, Cetylpyridinium Chloride, and alcohol. The composition varies across brands.


What are chemisterilants?

These are the chemicals used for sterilization. They are 2% Gluteraldehyde (cidex), Ethylene Oxide (EO), Formaldehyde + steam and Beta –Propiolactone (BPL).


Which Iodine compounds are used in antiseptics?

Tincture Iodine - 2% of Iodine in 70% alcohol - Iodophore - Povidone Iodine.


Name some antiseptics.

Chlorhexidine, Chloroxylenol, spirit (70% alcohol), tincture of Iodine, H2O2.


Which is the best disinfectant used in serology?

Sodium hypochlorite or Calcium hypochlorite


How are the clinical specimen disinfected before discarding?

By treating them with disinfectant, boiling or autoclaving and finally by incineration.


How are the articles commercially sterilized?

Gamma rays, Electron beams and Ethylene oxide.


How are hemodialyzers and endoscopes disinfected?

Gluteraldehyde or a combination of peracetic acid and hydrogen peroxide can be used.


How does Ethylene Oxide sterilize?

Alkylation (hydrogen atom is replaced with an alkyl group) of protein, DNA, and RNA affects bacterial metabolism and replication. EO gas (8.5%) is often mixed with stabilizers such as CO2 (91.5%) or hydrochlorofluorocarbons (HCFC). This requires high humidity (40-80%) and long exposure times (1-6 hrs).


What is Duckering?

Ducking is a process of inactivation of Anthrax spores in animal products such as wool, hairs or bristles. It was introduced by Elmhirst Duckering, an enginer at wool factory. This is a five-step process, each lasting for 10 minutes and carried out at 40.5°C.

What are the various filters?

Porcelain filters, Seitz (asbestos) filters, Sintered glass filters, Membrane filters and HEPA filters.


What are the uses of inspissator?

It disinfects and solidifies egg and serum containing media such as LJ medium and Loeffler’s serum slope.


How is operation theatre sterilized?

By fumigation with formaldehyde.


What is meant by cold sterilization?

Use of high-energy radiation such as gamma rays to sterilize an article.


How is milk pasteurised?


How are disinfectants tested?

Rideal Walker test, Chick Martin test, Kelsey & Sykes test and in-use test.


What is tyndallisation?

It is also known as fractional sterilization or intermittent sterilization where steaming is done at 100°C for 30 minutes for 3 successive days. Spores that germinate after the first day are killed the next day.


What are the different biological controls for sterilization?

Spores of Bacillus subtilis var niger is used to test hot air oven and spores of Geobacillus stearothermophilus is used to test autoclave, low temperature steam-formaldehyde sterilization and Ethylene oxide sterilization.


How are prions inactivated?


What is plasma sterilization?

When Hydrogen peroxide (H2O2) is subjected to electric field, which is generated using radio frequencey energy, it becomes ionized and assumes fourth state of matter - the plasma. It contains charged ions (free radicals) , which interacts with cell components (e.g., enzymes, nucleic acids) and thereby disrupt the metabolism of microorganisms.