Sterilization is the process by which sterility is achieved.

There are no degrees of sterility. An object, surface, or substance is, or is not, sterile.

If it is sterile it contains no cells or organisms present, nor viable organisms.

Also if the material is sterile and protected against contamination, the sterile condition will remain indefinitely. Disinfection implies that the material has been treated to eliminate or reduce the risk of pathogenic organisms, but does not imply that all viable organisms have been inactivated. Sterilization procedures are applied to:

• Ensuring that a process or experiment is carried out only with the desired organism.
• Allow the safe use of the products.
• Avoid environmental contamination.
• Prevent the deterioration of a product.

Sterilization is accomplished by either removing viable organisms, such as by filtration, or by killing them in one of the following ways:

• Heating in the presence or absence of water, that is, Dry Heat or Moist Heat.
• Irradiating with ultraviolet, gamma or X-ray radiation.
• Dealing with chemical products in suspension or another gaseous form, among which the use of Ethylene Oxide stands out.

The choice of agent depends on the circumstances, existing services, nature of the material or equipment to be sterilized, and its cost.

For products that can be sterilized in their final container, the choice of the method must take into account the influence it can have on the quality of the product.

Sterilization can be done by one of the methods described below. Modifications of these methods, and other methods, can be used (2), provided that their efficacy is demonstrated.

Sterilization by Moist Heat in general is the most recommended and widespread method for those materials that can withstand the conditions that the process implies.

Thus, sterilization with saturated steam is recommended, the reference conditions being heating at 121 °C for 15 min. Other combinations of temperature and time can be used as long as they are proven to be effective.

Dry Heat Sterilization, different times and temperatures can be used, the best known being:

• at 180° C for at least 30 minutes
• at 170° C for at least 1 hour
• at 160° C for at least 2 hours

In certain cases, other combinations of temperature and duration may be justified and authorized as long as the condition of sterility is demonstrated.

Radiation sterilization: treatment with gamma radiation or electron emission at a sufficient absorption dose to achieve the level of safety prescribed for the product to be sterilized (3).

Sterilization by Ethylene Oxide (or formaldehyde): It is carried out under appropriate conditions of gas concentration, temperature, contact time and relative humidity to allow the rehydration of the microorganisms in the product to be sterilized. Gas sterilization conditions must ensure the penetration of gas and moisture into the product to be sterilized. Sterilization must be followed by a gas elimination process under conditions that have made it possible to demonstrate, in preliminary experiments, that the concentration of residual gas or gas transformation products in the sterilized product is lower than the concentration likely to cause effects. toxic during the use of the product (4).

For all sterilization methods, the critical conditions of the operation must be controlled to ensure that all units in the batch have been subjected to at least the minimum sterilization conditions.

The duration of the treatment is measured from the moment in which the prescribed conditions for sterilization are achieved in the set of products to be sterilized.

It is essential that rigorous controls are carried out on products that will be packaged as “sterile”, a term that only implies that said product has satisfied the requirements of an approved sterility test.

Those controls should then ensure, as much as possible, the absence of viable microorganisms in those products.

There are basically two types of control.

• 1 Sterilization process controls, PE. Sterilization Controls or Sterilization Indicators
• 2 Sterility test of the products on themselves.

It is impossible to experimentally verify the term “sterile” in the sense that sterility tests concern only a relatively narrow range of evaluations, for example, the methods do not guarantee detecting all known types of microorganisms. Furthermore, because only a small proportion of the series of processed materials can be evaluated, sterility tests are considered best as long as the evaluations are carried out under limiting conditions.

This paper will briefly address the principles and applications of various methods of monitoring and validation of sterilization processes.

There are basically three types of sterilization indicators, physical indicators, chemical indicators and biological indicators.

Básicamente que el material no ha alcanzado la condición de esterilidad y por tanto no se ha logrado destruir totalmente los diferentes tipos de microorganismos contaminantes que pudieran encontrarse en los materiales procesados. Es esencial mostrar que los microorganismos crecerán realmente bajo las condiciones de la prueba. Por esta razón los controles positivos tienen que demostrarse y debe ser calculada la factibilidad de crecimiento de pequeñas cantidades de microorganismos idóneos en los medios de cultivo. La Farmacopea inglesa estipula el uso de Staphylococcus aureus, Clostridium sporogenes y Candida albicans para controles aeróbicos, anaerobios y micóticos positivos, respectivamente.

A sterility test must be carried out under the conditions studied to eliminate any risk of accidental contamination of the product during the test, for example using sterile air laminar flow hoods. The precautions taken to avoid such contamination should not affect the microorganisms whose presence is to be revealed in the test.

The effectiveness of the precautions observed must be regularly verified by a control of the air and of the work surfaces, carrying out parallel controls of preparations known to be sterile.

The techniques discussed in this paper comprise an attempt to achieve, where possible, continuous control of a particular sterilization process. The sterility test by itself does not provide a guarantee as to the sterility of a Lot or Serial; however, it is an additional check, and continued compliance with the test provides confidence in the effectiveness of the sterilization or aseptic process. The failure to perform a sterility test, despite its major criticism highlighting its inability to discern anything other than gross contamination, can have important legal and moral consequences.