Methods of sterilisation and disinfection

Methods of Sterilisation

Sterilisation is the process of killing or removing all microorganisms, including bacterial spores which are usually resistant, from an object or a material.

Heat Sterilisation

One of the most common methods of sterilising is by heat, which kills microorganisms by denaturing their proteins.
Heat Sterilisation is of two types: Dry heat and Moist heat.
Dry heat sterilisation (direct flaming) involves exposing the material to a flame which will burn the microorganisms.
Moist heat sterilisation involves steaming the material to be sterilised.
The effectiveness of heat sterilisation is dependent on the time of exposure and the temperature used.

Pressure Sterilisation (Autoclaving)

Autoclaving is a type of pressure sterilisation. It involves using steam under pressure or gas to kill microorganisms.
Autoclaves are essentially pressure cookers. They use steam heated to 121-134°C under pressure to sterilise equipment or other objects.
This method is efficient because it takes less time and is generally more reliable due to the penetration power of pressurised steam.

Sterilisation using Chemicals

Chemical sterilants work by destroying the cell wall and inhibiting cellular functions. Examples include ethylene oxide and formaldehyde.
These sterilants are used on heat-sensitive medical equipment.

Disinfection is the process of reducing the number of pathogenic microorganisms to make them safe.

High, Intermediate, and Low-Level Disinfectants

Disinfectants are classified based on their effectiveness: High-level, Intermediate-level, and Low-level disinfectants.
High-level disinfectants kill almost all types of bacteria, viruses, fungi, and spores. They are used for sterilising medical equipment.
Intermediate-level disinfectants are effective against bacteria, most viruses, and fungi, but not spores.
Low-level disinfectants are used to disinfect noncritical medical devices and environmental surfaces. They can kill most bacteria, some viruses, and some fungi, but are not effective against spores.

Disinfection by Physical Methods

Physical methods of disinfection include heat, radiation, and filtration.
Heat can be used to disinfect water, surfaces, and air.
Radiation (UV or ionising radiation) can be used to disinfect air, water, and surfaces.
Filtration is a method used for the purification of air and liquids where bacteria may be present.

Chemical Disinfection

Chemical disinfectants can be in the form of gases, liquids or solids. Different types of disinfectants are used for different purposes, and their effectiveness varies.
Some common categories of chemical disinfectants include alcohols, aldehydes, oxidising agents, phenolic compounds, and quaternary ammonium compounds.
It is important to note that disinfectants are harmful and must be used as per guidelines.

Any disinfection or sterilisation procedure mustn’t harm the user, the material being disinfected or sterilised, or the environment.
Personal Protective Equipment (PPE) must be used when handling chemical sterilants and disinfectants.
Disinfectants and sterilants must be stored properly to prevent spills and accidents. Also, they should not be stored near food items.
It is essential to understand and follow the instructions indicated on the labels of disinfectants and sterilants.