Frequently asked questions in sterilisation and disinfection @ Sridhar Rao P.N's home page

Frequently asked questions in sterilization and disinfection

1. 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.

2. What is the temperature and time employed to sterilize the articles in hot air oven?
- 160^oC for 60 minutes.

3. What are the conditions of sterilization in an autoclave?
- 121^oC for 15 minutes at 15 pounds pressure.

4. What are the articles sterilized in a hot air oven?
- Glassware’s, metallic instruments like scissors and forceps, swabs, powder, oils and grease.

5. What are the articles sterilized in an autoclave?
- Culture media, gloves, cotton and clothes.

6. How are heat labile fluids such as serum and antibiotic solutions sterilized?
- By filtration.

7. How is air sterilized?
- By High Efficiency Particulate Air (HEPA) filters.

8. Name some disinfectants?
- Phenol, Lysol, Formaldehyde, Sodium hypochlorite.

9. What are antiseptics?
- Antiseptics are mild disinfectants that can be safely used on skin and mucous membranes.

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

11. Which Iodine compounds are used in antiseptics?
- Tincture Iodine - 2% of Iodine in 70% alcohol - Iodophore - Povidone Iodine.

12. Name some antiseptics.
- Chlorhexidine, Chloroxylenol, spirit (70% alcohol), tincture of Iodine, H₂O₂.

13. Which is the best disinfectant used in serology?
- Sodium hypochlorite.

14. How are the clinical specimen disinfected before discarding?
- By treating them with disinfectant, boiling or autoclaving and finally by incineration.

15. How are the articles commercially sterilized?
- Gamma rays, Electron beams and Ethylene oxide.

16. What are the various filters?
- Porcelain filters, Seitz (asbestos) filters, Sintered glass filters, Membrane filters and HEPA filters.

17. What are the uses of inspissator?
- It disinfects and solidifies egg and serum containing media such as LJ medium and Loeffler’s serum slope.

18. How is operation theatre sterilized?
- By fumigation with formaldehyde.

19. What is meant by cold sterilization?
- Use of high-energy radiation such as gamma rays to sterilize an article.

20. How is milk pasteurised?
- Holder method: Milk is heated at 62^oC for 30 minutes and then cooled rapidly to 13^oC.
- Flash method : Milk is heated at 72^oC for 15 seconds and then cooled rapidly to 13^oC.

21. How are disinfectants tested?
- Rideal Walker test, Chick Martin test, Kelsey & Sykes test and in-use test.

22. What is tyndallisation?
- It is also known as fractional sterilization or intermittent sterilization where steaming is done at 100^oC for 30 minutes for 3 successive days. Spores that germinate after the first day are killed the next day.

23. 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.