Microbiology and Hygiene: Sterilisation, Disinfection and Precautions
What this domain tests
Microbiology and Hygiene tests microbes, sterilisation and disinfection, standard precautions, hand hygiene, immunisation and hospital-acquired infection. The exam contrasts what kills spores with what does not.
Core rules
- Bacteria are prokaryotes; viruses need a host cell; fungi include yeasts and moulds. Gram staining divides bacteria into Gram-positive (purple) and Gram-negative (pink).
- Sterilisation destroys all microbes including spores. Autoclave: 121 °C at 15 psi for 15–20 minutes. Disinfection reduces pathogens but may not kill spores.
- Alcohol, boiling and most disinfectants do not reliably kill spores. Sterilise items entering sterile tissue or blood.
- Standard precautions apply to all patients: hand hygiene, gloves, gown, mask and eye protection based on risk, safe sharps handling.
- Hand hygiene: use alcohol-based rub for 20–30 seconds when hands are visibly clean; wash with soap and water when soiled or after body-fluid exposure.
- Cold chain: vaccines kept at 2–8 °C; avoid freezing DPT, hepatitis B and tetanus toxoid.
Worked example
A theatre technician loads an autoclave but the air is not fully removed. Reasoning: trapped air prevents steam contact, so the load may not reach 121 °C and spores can survive. The Bowie-Dick test detects air removal failure, and biological indicators such as Geobacillus stearothermophilus spores verify sterilisation. Do not release the load until the cycle and indicator checks pass; repack correctly and avoid overloading.
Traps
- Calling alcohol a sterilant.
- Using boiling as sterilisation for surgical instruments.
- Giving antibiotics for viral infections.
- Storing vaccines in the freezer door, where temperature fluctuates.