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What is Sterilization?

February 1st, 2014

Sterilization is a process used to render a product free from living microorganisms. Sterilization completely eliminates and destroys all forms of microbial life. Instruments that penetrate skin or mucosal membranes must be cleaned and sterilized to prevent cross infection. Sterilization can be accomplished by using steam, dry heat, or gas. Items must be mechanically cleaned with proper detergent and water to remove organic debris before sterilization. Steam sterilization is the most practical and economical method for sterilizing medical instrument.

Effective autoclaving depends on (1) proper cleaning before sterilization, (2) time of exposure, (3) temperature of steam, (4) saturation of steam, and (5) proper penetration of steam to the items to be sterilized. Recommended exposure time varies with temperature, material and whether the instrument is wrapped or not. Small tabletop autoclave (or steam sterilizers) that are carefully maintained can be used for many years and are highly recommended for clinic and office settings.

Sterilization monitoring

The sterilization process must be monitored to ensure the integrity of the process. The sterilization of equipment should be monitored using various indicators to ensure that the process has been effective:

Manual indicators on the machines, such as time, temperature and pressure gauges, must be monitored and recorded.

  • Temperatures must reach a specific level and be maintained for specific periods to kill microorganisms. The greater the temperature, the less time required.
  • Pressure is necessary to create the steam. Manufacturers set the pressure gauge.
  • Steam must be saturated for effective sterilization. Adequate water must be present to generate the required amount of steam. For tabletop autoclaves, water must be manually added.

Chemical indicators, such as “autoclave tape” that changes colour, are useful for distinguishing between processed and unprocessed items only. Autoclave tape does not, however, imply that sterilization has take place. Tapes are usually placed on wrapped products.

Biological indicators (BI) must be used regularly to ensure that sterilization has occurred. All biological indicators must be used according to the manufacturer’s instructions and records should be kept of these results. If biological indicator testing indicates that sterilization has not been achieved, sterility of the instruments cannot be assured. It is very importance that a process be in place in the event of a failure. If this occurs it is important to have a record describing the cause of the failure, corrective action and any recall of items.

Using biological indicators

Use of biological indicators (BI) is the gold standard for monitoring the sterilization process because they directly determine whether the most resistant microorganisms (e.g. Geobacillus or Bacillus species) are viable rather than merely determine whether the physical and chemical conditions necessary for sterilization are met. The use of biological indicator (BI) is recommended by all health agencies, medical and dental professional organizations.

A biologically indicator (BI) is made of a paper strip containing a set amount of bacterial spores. The classic BI is a paper strip with bacterial spores packaged individually in a glassine pouch. After use, this classic BI is sent to a laboratory for incubation and results will not be available for over one week.

The new generation of BI, such as the EZTest® from SGM Biotech is “self-contained” and can be activated and cultured without any special laboratory facilities or the services of a trained microbiologist. The complete process can be performed in the office or clinic with test results available in 24 hours.

The bacterial spores used in BIs are very resistant to chemicals, environmental changes and are very hard to kill. On the BI, the number of spores is far greater than the common microbial contaminants found on patient care equipment. If all the spores on the BI are killed by the sterilization process, one can safely assume that all other potential pathogens in the load have also been killed. Therefore, a negative BI test is a good indicator that the sterilization process is effective.