Explanation of Sterilization

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Sterilization: definition, explanations:

In microbiology, sterilization is a process used to remove living microorganisms from materials or objects, including in their resting stages. The material becomes sterile. The most prevalent method of sterilizing is heat.


Sterilization is any process, physical or chemical, that kills or destroys all contaminating microorganisms of a material, such as bacteria, viruses, microbes, spores, including the most resistant such as endospores, without taking account of their type.

The process renders sterile, even infertile. The sterilization process must be designed, validated, and implemented in such a way as to be able to eliminate the product’s microbial load or a more resistant microorganism.

Sterilizing agents that kill microorganisms are called microbicides or more commonly “germicides” (among biocides ); they result in disinfection.

If the agent specifically destroys bacteria, it is called bactericide; it is antisepsis. If it kills the fungi, it is called a fungicide. After exposure of the sterilized object to the air or its environment. It will again have been contaminated by microorganisms; the sanitation chain is broken.

Heat sterilization methods are generally the most commonly used to eliminate microorganisms, including the most resistant forms such as endospores. Thermal sterilization can take place by:

dry heat: also includes several phases : direct heat, flame sterilization (including incineration), and oven;
by moist heat: includes several modalities, boiling, pasteurization, and the use of the autoclave.

The absolute sterility of a substance or item cannot be shown without destroying all units of the batch of finished product; sterility is defined in probabilistic terms.

Where the risk of contamination of a unit of product is acceptable. When the chance of a microorganism being present in an active or latent form is equal to or less than 1 in 1,000,000, a critical product is considered sterile (sterility safety factor 10 -6 ).

Sterilization in medicine, economics:

For example in medicine, tubal sterilization or tubal ligation is a method of female contraception consisting of tying off the fallopian tubes.

Ultraviolet sterilization results in microbial destruction using powerful UV – C ( germicidal ) light.

In economics, sterilization is an operation in the financial markets carried out by the central bank of a country to neutralize the possible negative consequences of currency transactions.

Microbial rate:

When a bacterial population is treated with chemicals or heat, it usually dies at a steady rate. For example, if we assume that we have a population of 2 million microorganisms that have been processed for one minute and 90% of the population is dead.

We now have 200,000 microorganisms left. If the population is treated for one minute, 90% of the remaining population will be exterminated, resulting in 20,000 microorganisms. If the mortality curve is plotted logarithmically, the mortality rate is constant.

Sterilization and debates:

The term “germ-free “, also used in place of “sterile”. any stage of development. The term “germ-free” is associated with the incorrect name “germs” for microorganisms at any stage of development, even in an active state.

The sterilization of materials (food, pharmaceuticals, solutions), medical instruments, implants, objects, packaging, devices (e.g. endoscopes), and containers (e.g. for the culture of microorganisms)

Kills all contained or adherent microorganisms, including their permanent forms (e.g. spores), and destroys viruses, prions ( infectious proteins ), plasmids and other DNA fragments.

In practice, complete sterilization is not 100% successful with certainty. It is therefore a reduction in the number of microorganisms capable of reproducing by a factor determined by the field of application.

For example, the residual content of microorganisms capable of reproduction in one unit of the sterilized material must be at most 10 -6 colony-forming units, that is, in one million units of the sterilized product treated in the same way, a maximum of one micro-organism capable of reproducing can be contained.

Thermal sterilization:

For sterilization by heating, the kinetics of destruction of microorganisms is important. Dying in a population of microorganisms resembles the decay of radioactive elements in that the number of surviving non-replicating microorganisms decreases exponentially over time (like the number of unhardened atoms of an element radioactive).

As a general rule, for sterilization, the number of living individuals should be six orders of magnitude.  A 10 -5 reduction needed. The actual number of organisms depends on the initial number.

Which may be difficult or impossible to determine depending on the task. Therefore. It is best to interpret the decimal reduction time as a probability of survival.

A microorganism has a 10% chance of survival when exposed to the conditions. Theoretically, the probability of survival is never zero.

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