Question
Define sterilization and disinfection. Name the best method of heat sterilization temperature/s employed and holding periods. Describe the working of above instrument and its applications in hospital and lab. What are the sterilization controls used. (2+2+4+2)
Answer
Definitions Sterilization is the complete destruction or removal of all forms of microbial life, including the most resistant bacterial spores, from an object or surface. Disinfection is the elimination of most pathogenic microorganisms (but not necessarily bacterial spores) from inanimate objects, reducing the microbial load to a level not harmful to health — a less absolute process than sterilization.
Best method of heat sterilization — temperature and holding period Moist heat sterilization by autoclaving is regarded as the best, most reliable method: 121°C at 15 lbs/sq inch pressure, held for 15–20 minutes (longer holding times, e.g., 30 minutes, are used for larger loads or when specifically sterilizing rubber goods).
Working of the autoclave The autoclave is a double-walled chamber in which steam is generated (either from an internal water reservoir or supplied externally) and admitted into the chamber. Raising the pressure inside the sealed chamber raises the boiling point of water correspondingly, so steam at 15 lbs/sq inch reaches 121°C — well above the 100°C achievable at atmospheric pressure. Air, a poor heat conductor, must be fully displaced/evacuated from the chamber (via a discharge valve, or a vacuum pump in modern models) for the set temperature to be reliably achieved throughout the load — incomplete air removal is a common cause of sterilization failure. At 121°C, the steam’s latent heat is released onto contact with cooler surfaces, causing rapid protein denaturation/coagulation of microorganisms, including their most heat-resistant spores. After the holding period, steam is released and the chamber is allowed to cool before opening.
Applications: sterilization of surgical instruments, dressings, culture media, glassware, and rubber goods (gloves, tubing) in hospitals and laboratories; not suitable for heat/moisture-sensitive materials (some plastics, oils, powders, sharp cutting instruments that could be blunted).
Sterilization controls
- Physical controls — autoclave gauges/charts recording temperature, pressure, and time achieved during each cycle.
- Chemical indicators — autoclave tape (changes colour/develops stripes on exposure to the correct temperature) and the Bowie-Dick test (confirms effective air removal and steam penetration).
- Biological indicators — spore strips of a highly heat-resistant organism, Geobacillus stearothermophilus, are processed alongside the load; absence of growth on subsequent incubation confirms that true sterilizing conditions were achieved throughout the load, not merely that the machine completed its cycle — the most definitive control.