Sterilisation
- Removal of viable microorganisms including spores and viruses
- Can be achieved by:
- Autoclaves
- Hot air ovens
- Ethylene oxide
- Low-temperature steam and formaldehyde
- Sporicidal chemicals
- Irradiation
- Gas plasma
Autoclaves
- Steam under pressure has a higher temperature than 100 °C
- To be effective against viruses and spore forming bacteria need to
- Have steam in direct contact with material
- Vacuum has to be created
- Need to autoclave for 3 min at 134 °C
or 15 min at 121 °C
- Check performance by colour changes on indicator tape
- Autoclaves are highly effective and inexpensive
- Unsuitable for heat-sensitive objects
Hot ovens
- Inefficient compared to autoclaves
- Requires temperatures of 160 °C
for 2 hours or 180 °C
for 30 min
Ethylene oxide
- Highly-penetrative and active against bacteria, spores and viruses
- Also flammable, toxic and expensive
- Leaves toxic residue on sterilised items
- Instruments therefore need to be stored for prolonged period before use
- Suitable for heat-sensitive items
Sporicidal chemicals
- Often used as disinfectants but can also sterilise instruments if used for prolonged period
- Inexpensive and suitable for heat-sensitive items
- Toxic and irritants
- 2% Gluteraldehyde is most widely used liquid sporicidal chemical
- Most bacteria and viruses killed within 10 minutes
- Spores can survive several hours
Irradiation
- Gamma rays and accelerated electrons are excellent at sterilisation
- Used as an industrial rather than hospital based method
Disinfection
- a reduction in the number of viable organisms
- Can be achieved by:
- Low-temperature steam
- Boiling water
- Chemical disinfectants
Low-temperature steam
- Most bacteria and viruses are killed by exposure to moist heat
- Usually achieved with dry saturated steam at 73 °C
for greater than 10 minutes
- Effective and reliable and suitable for instrument with a lumen
- Unsuitable for heat-sensitive items
Chemical disinfectants
- Destroys microorganisms by chemical or physicochemical means
- Different organisms vary in their sensitivity
- Gram-positive - highly sensitive
- Gram-negative - relatively resistant
- Clostridial & mycobacterial species - very resistant
- Slow viruses - highly resistant
- Disinfectants are suitable for heat-sensitive items
- Less effective than heat
- Chemicals used include:
- Clear soluble phenolics
- Hypochlorites
- Alcohols
- Quaternary
ammonium compounds
Bibliography
Rutala W A, Weber D J. New disinfection and sterilisation methods. Emerg Infect Dis 2001;
7: 348-353.
Rutala W A, Weber D J. Infection control: the role of disinfection and sterilisation.
J Hosp Infect 1999; 43 (Suppl): S43-55. |