Sterilization – Methods of sterilization | Biology Ideas

Sterilization and disinfection

Sterilization – Means freeing of any object or substance from all living organisms or it can be referred to the as complete destruction of all forms of life, including bacteria, fungi, viruses, and spores.

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The four main reasons for killing or removing or inhibiting microorganisms are –

To prevent infection of man, his animals, and plants.

To prevent spoilage of food and other commodities.

To prevent contaminating microorganisms in various pure culture processes.

To prevent contamination in industrial processes.

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Definitions of some terms –

Disinfection – means the killing or removal of microorganisms capable of causing infection. Disinfection does not necessarily include sterilization.

Disinfectant – is an agent accomplishing disinfection.

Antiseptics – are substances that kill or inhibit microorganisms especially in contact with the body.

Bacteriocide – Any substance or agent that kills bacteria is a bacteriocide or bactericidal agent. The same suffix is also used as germicide, viricide, algicide and fungicide. ( cide = killer ).

Sepsis – is the growth of harmful microorganisms in contact with living tissue.

Asepsis – In strict sense asepsis is the absence of infectious organisms in living tissue. However, the term is usually applied to any technique designed to keep all unwanted organisms out of any field of work or observations. The work of microbiologists and surgeons involves aseptic techniques.

Microbiostasis – stasis is a Greek word meaning “to stand still”. The agents or conditions that bring about stasis do not immediately kill the microorganisms but inhibit multiplication e.g. bacteriostatic, fungistatic, etc.

Sanitizer – This may be defined as any agent that reduces the bacterial count to safe levels as may be judged by public health requirements. Sanitizers are commonly applied to inanimate objects such as eating and drinking utensils and food handling equipment.

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Methods of sterilization

1] Physical Methods

1) Heat

Dry heat

Moist heat

2) Radiation

Ultraviolet radiation

Ionizing radiation

3) Filtration

Granular filters

Fibrous filters


2] Chemical methods

Use of gases

Use of fumigants

Use of solutions


The method of choice depends upon –

The material to be sterilized.

Susceptibility of the material to deterioration on contact with the sterilizing agent.

The intensity and extensiveness of microbial killing required.

The environmental conditions under which the sterilization process is to be carried out.

In general, heat is most commonly employed as it is the simplest and most reliable method.

Heat labile substances are sterilized by using filtration.

Chemical substances are less reliable than heat and are used mainly for disinfection purposes (i.e. killing of vegetative forms of bacteria and not their spores).


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