Autoclaving and sterilization

Principle

• Sterilization destroys all microbial life, including bacterial spores; disinfection reduces pathogens but not necessarily spores.
• An autoclave uses saturated steam under pressure; moist heat denatures and coagulates proteins more efficiently than dry heat.
• Standard cycle: 121 °C at about 15 psi (about 103 kPa above atmospheric pressure) for at least 15 minutes for small clean loads.

Reagents and equipment

• Gravity displacement or pre-vacuum autoclave, autoclave bags and trays, chemical indicator tape, biological indicators.

Procedure

• Air must be removed so steam contacts all surfaces; pre-vacuum units remove air mechanically.
• Loosen caps, do not overfill containers, and leave space between items; place bags in secondary trays and leave them slightly open (add a little water per policy).
• Longer times are needed for large volumes of liquid and biohazardous waste (often 30–60 minutes or more, validated for the load).
• Pre-vacuum cycles at 134 °C use shorter times (e.g. about 3–4 minutes for instruments); prion decontamination uses special extended protocols.
• Wait for pressure to return to zero and cool before opening; wear heat-resistant gloves, gown and face protection.

Quality control and pitfalls

• Chemical indicator tape only shows exposure to heat, not sterility.
• Biological indicator: Geobacillus stearothermophilus spores, run at least weekly (or per policy), incubated at about 55–60 °C; growth means sterilization failed.
• Bowie–Dick test daily for air removal in pre-vacuum units.
• Record time, temperature and pressure for every cycle; keep maintenance logs.
• Overpacking, sealed containers and trapped air cause failures.
• Never autoclave flammable, volatile, corrosive or radioactive materials, or bleach-treated waste.

Clinical use

• Sterilizing culture media (typically 121 °C for 15 minutes; heat-sensitive supplements are filter-sterilized and added after cooling to about 45–50 °C), glassware and instruments, and decontaminating infectious waste.
• Other methods: dry heat (e.g. 160 °C for 2 hours or 170 °C for 1 hour), membrane filtration (0.22 µm), ethylene oxide, hydrogen peroxide plasma and radiation.