Equipment Sterilisation

Introduction

Sterilisation is the use of physical or chemical means to destroy all organisms, including microbial spores and viruses. There are several techniques that can be used;

• Heat
• Irradiation
• Filtration
• Chemicals

Other techniques include freezing, lysis, dessicationa and ultrasonification, but these are not often employed due to lower efficiency

Heat

Due to cost-effectiveness, efficiency and ease-of-use, heat is the preferred method of sterilisation.

Dry heat Hot air can be used to sterilise items such as glassware, although due to poor diffusion and penetration this method is not as efficient as moist heat.

• Incineration- useful for items such as bandages and paper dishes
• Oven baking- useful for items not containing water and not readily permeable by steam, e.g. wood, glass syringes.
• Sterilisation in this case normally means processing at 171 degrees for over an hour

Moist heat The most effective form of heat sterilisation is saturated steam under pressure

• Achieved using an autoclave
• Pressure aids the penetration of the steam into materials
• Used to sterilise heat resistant materials and pharmaceuticals

Immersion in boiling water

• Kills vegetative bacteria, but not all bacterial spores
• Addition of 2% sodium bicarbonate improves efficiency

Pasteurisation

• Used to reduce bacteria in fluids

Irradiation

Gamma radiation is the method of choice for sterilising large batches of items such as needles and syringes

• Although the cost is high, the process is 100% effective
• Mechanism involves production of free radicals- destroys DNA

Ultraviolet radiation is not normally used as its efficiency as a sterilant is low

• Requires direct exposure
• It is used however in hospitals to stop the growth of bacteria in water, e.g. air hoods in virology laboratories

Filtration

Used to produce particle and pyrogen-free fluids

• Work by electrostatic attraction and physical pore size

Chemical agents

Although the use of chemical agents has been overtaken by the development of gamma radiation techniques, two alkylating gases are still used:

• Ethylene oxide- used to sterilise single-use medical items such as heart valves
  • Not often used due to high toxicity
• Formaldehyde- used to decontaminate rooms, e.g. isolation rooms
  • Irritates mucuos membranes
  • Relatively high humidity required for effectiveness