Decontamination and Sterilization

The first prerequisite for any decontamination procedure is adequate pre-cleaning of the device or surface to be decontaminated. Organic material including blood and soil may inactivate chemical disinfectants and protect microorganisms from the decontamination process. The actual physical removal of microorganisms by scrubbing is often as important as the antimicrobial effect of the cleaning agent used.

Select a chemical disinfectant that is labeled as approved for use as a "hospital disinfectant" and is tuberculocidal when used at recommended dilutions. Cells of M. tuberculosis are among the most resistant vegetative microorganisms known and constitute a formidable challenge to a chemical disinfectant. A disinfectant that is tuberculocidal can be expected to control many types of less resistant pathogens. Hospital disinfectants suitable for decontaminating the surfaces of scientific equipment include the following generic formulations: iodophors; chlorine solutions; alcohol (isopropyl, ethyl); phenolic compounds and quaternary ammonium compounds. Wescodyne (an iodophor) and sodium hypochlorite (bleach) are available in the NIH self-service stores.

Considerations

• Choose a disinfectant that is not corrosive or otherwise destructive to the items undergoing decontamination.
• Read and follow the manufacturer's label directions concerning the recommended disinfectant concentration, contact time and method of application.
• Wear the appropriate gloves, lab coat and eye protection whenever using chemical disinfectants.
• Determine if the design of the equipment or its construction materials will have an effect on the decontamination process. Crevices, joints and pores constitute barriers to the penetration of liquid disinfectants. Prolonged contact time may be required to accomplish decontamination, depending on the intricacy of the design and the amount of soil present.

Select an appropriate disinfectant contact time. The longer the exposure to the chemical agent, the more likely that all pertinent microorganisms will be inactivated. A contact time of 10 minutes may not be adequate to disinfect an item, especially one that is difficult to clean because of narrow channels or other areas that can potentially harbor microorganisms. Longer exposure times, i.e. 20 to 30 minutes, may be necessary. This is especially true when high-level disinfection is to be achieved.

• Table 1 Methods of Disinfection
• Table 2 Levels of Germicidal Action

For guidance regarding the treatment of equipment contaminated with a mixture of chemical, radiological and biological hazards, contact your Safety and Health Specialist.

Tables adapted from: Favero, M.S. (1985), Sterilization, disinfection, and antisepsis in the hospital, pp. 130 and 133. In Manual of Clinical Microbiology, 4^th edition, ASM, Washington, D.C.

NOTE: The NIH does not recommend or support the use of ultraviolet (UV) radiation in laboratories. Although UV is effective against most microbes, it requires an understanding of its abilities and limitations. The 253.7-nm wavelength emitted by the germicidal lamp has limited penetrating power and is primarily effective against unprotected microbes on exposed surfaces or in the air. It does not penetrate soil or dust. The intensity or destructive power decreases by the square of the distance from the lamp. Thus, exposure time is always related to the distance. The intensity of the lamp diminishes over time. This requires periodic monitoring with a UV meter. The intensity of the lamp is drastically affected by the accumulation of dust and dirt on it. The bulbs require frequent maintenance. In addition, there are safety hazards associated with the use of UV that require personal protective equipment or other safety devices to protect users. UV lights in biosafety cabinets require the cabinet be decontaminated prior to performing maintenance on the system.

Past experience has proven that good techniques in conducting experiments are highly effective in preventing contamination. The use of UV radiation does not eliminate the necessity for using good practices and procedures.

Tables adapted from: Favero, M.S. (1985), Sterilization, disinfection, and antisepsis in the hospital, pp. 130 and 133. In Manual of Clinical Microbiology, 4^th edition, ASM, Washington, D.C.