Microbiology and Sterilization/Disinfection Practice
Microbiology and sterilization practice test microbial structure, culture, infection control and the choice of sterilization or disinfection method. Safety and validation are central.
Core rules
- Sterilization destroys all microorganisms including spores; disinfection reduces pathogens but may not kill spores. Autoclaving uses steam at 121°C, 15 psi for 15 to 20 minutes. Dry heat uses 160°C for 2 hours or 170°C for 1 hour.
- Heat-labile fluids and vaccines are filtered through 0.22 micrometre filters. Ethylene oxide is used for heat-sensitive plastics. Seventy percent alcohol is more effective than absolute alcohol because water aids protein denaturation.
- Biological indicators: Geobacillus stearothermophilus for moist heat; Bacillus atrophaeus for dry heat and ethylene oxide.
Worked example
An autoclave load fails its spore test. Air trapped in the chamber or load prevents steam contact, so the required temperature is not reached throughout. The load is not sterile; investigate packing, air removal and cycle validation before reuse.
Traps
Disinfection is not sterilization. Boiling does not reliably kill spores. Do not use alcohol on all surfaces or as a sterilant. Concentration, contact time and organic matter all affect disinfectant action.