Sterilization, Disinfection, & Decontamination

Sterilization

Any item, device, or solution is considered to be sterile when it is completely free of all living microorganisms, including bacterial endospores.  Sterilization can be accomplished by heat, hydrogen peroxide gas, chlorine dioxide gas, plasma, ozone, and radiation.

Steam sterilization using an autoclave is effective as the moisture available in the load is heated under pressure to sterilize the material.  The moisture is critical for the sterilization to occur.  For this reason, if  a bag must be sealed prior to autoclaving, sufficient water should be added to the bag.  Flammable or other hazardous chemicals, including bleach should never be autoclaved without proper containment to prevent damage to the autoclave or its pipelines.

To ensure effective sterilization, the temperature is monitored with appropriate temperature indicator placed inside one of the bags, and a validation is preformed to evaluate the sterilization efficiency using a spore strip or other biological indicator.

Disinfection

Disinfection is generally a less lethal process than sterilization that reduces the overall level of microbial contamination. It eliminates nearly all recognized pathogenic microorganisms but not necessarily all microbial forms (e.g. bacterial spores) on inanimate objects. The effectiveness of a disinfection procedure is controlled significantly by a number of factors, each one of which may have a pronounced effect on the end result.  Among these are:

• Nature and number of contaminating microorganisms including susceptibility
• Amount of organic matter present (e.g.dirt, feces, blood)
• Type and condition of instruments, devices, and materials to be disinfected
• Temperature
• Contact time
• Environmental stability and shelf-life

All chemicals are not equally effective against different types of microorganisms.  Different chemicals have  different modes of action and levels of activity.  It is important to understand the mode of action to select the appropriate chemical.  It is also essential that the contact time be sufficient to allow for the action of the chemicals on the microorganisms.  Laboratorians should be sure to follow the manufacturer's instructions for the use of all disinfectants, including preparing fresh solutions as necessary.

Decontamination

Decontamination renders an area, device, item, or material safe to handle (i.e. safe in the context of being reasonably free from risk of disease transmission). The primary objective is to reduce the level of microbial contamination so that infection transmission is eliminated. The decontamination process may be ordinary soap and water cleaning of an instrument, device, or area. In laboratory settings, decontamination of items, spent laboratory materials, and regulated laboratory wastes is often accomplished by a sterilization procedure such as steam autoclaving.

The presence of organic matter necessitates longer contact time with a decontamination method if the item or area has not been cleaned prior. Decontamination in laboratory settings often requires longer exposure times because pathogenic microorganisms may be protected from contact with the decontaminating agents.

Chemical germicides used for decontamination range in activity from high-level disinfectants (i.e. high levels of bleach), which may be used to decontaminate spills of cultured or concentrated infectious agents in research or clinical laboratories, to low-level disinfectants or sanitizers for general housekeeping purposes or spot decontamination of environmental surfaces in health care settings.  Resistance of selected organisms to decontamination is presented  below from least resistant to most resistant:

• Lipid viruses - Least Resistant
• Bacteria 
• Fungi 
• Non-lipid viruses
• Mycobacteria
• Bacterial spores
• Prions - Most Resistant

Ultraviolet Treatment

UV light was commonly used for disinfection in pass boxes, BSCs and PCR stations.  The efficacy of UV light for disinfection is limited by a number of factors.  UV light has poor penetration, and only those microorganisms directly bathed in it will be affected.  UV lights will require regular cleaning, monitoring, and periodic replacement to ensure germicidal activity.

Wavelengths below 280nm cause chemical reactions and therefore have germicidal action.  UV light will only be effective on exposed surfaces such as the interior of a BSC and not on items where there is no direct contact of the UV radiation with the item (i.e. under other items or in shadowed areas). Personnel should avoid exposure to light in this wavelength region since brief exposure can cause erythema, harming skin and eyes.

For additional information related to sterilization, disinfection and decontamination please refer to Appendix B in the Biosafety in Microbiological and Biomedical Laboratories guidelines (BMBL) 6th ed.