Factors Affecting the Efficacy of Disinfection and Sterilization

    If we want to achieve the desired sterilization or disinfection results, we have to first know what factors will affect these processes. Some of which are related with bacteria themselves, others of which are related with chemical and external physical conditions, and even might be operator error. After we clearly know these factors, we can avoid many risks of incomplete sterilization.

1. Quantity and Location of Microorganisms

    The lager the quantity of microorganisms, the more time or the more amount of disinfectant needs to damage all of them. The location of the microorganisms is equally important, because instruments that have crevices, joints, and channels are more difficult to disinfect than instruments that have flat-surfaces. If the instruments are consist of multiple pieces, then it must be disassembled.

Bacterial spore

2. Resistance of Microorganisms

    Many organisms have innate resistance to certain germicides, so choosing a proper germicide or sterilization process is important. For example, spores are resistant to disinfectants, ultraviolet radiation, high temperature, dryness and freezing, therefore, they required a longer exposure time or higher concentration of germicide than less resistant microorganisms.

3. Concentration and Potency of Disinfectants

    If everything else is constant then the higher concentration of the disinfectant, the greater its efficacy and the shorter the time to kill all the microorganisms. The potency of a disinfectants affects the exposure time required to achieve the same level of germicidal activity.

4. Physical and Chemical Factors

    There are several physical and chemical factors influence the efficacy of disinfectants, including temperature, pH, relative humidity and water hardness.
    Generally, as the temperature increases, the activity of most disinfectants increases. But if the temperature is too high then it might cause the disinfectants to degrade and the germicidal activity will decline. As the pH increases, the antimicrobial activity might increase in some disinfectants, such as glutaraldehyde, but decreases in others such as phenols. This effect is caused by altering the germicidal molecule or the cell surface. Relative humidity influences the activity of gaseous disinfectants/sterilants, such as chlorine dioxide and formaldehyde. Water hardness reduces the rate of killing microbes of some disinfectants, because divalent cations such as magnesium and calcium in hard water will interact with disinfectant forming insoluble precipitates.

5. Organic Matter

    Organic matter such as serum, blood, pus, fecal or saliva can influence the antimicrobial activity of disinfectants in at least two ways.

    First, disinfectant and organic matter can occur chemical reaction and forming a complex which is less germicidal or non-germicidal. Second, organic matter may protect microbes from attack by acting as a physical barrier.

    Therefore, it is very important to clean the instruments with water and brushes before any sterilization or disinfection process.

6. Duration of Exposure

    Instruments must be exposed to the biocide for an appropriate minimum contact time. In general, the longer exposure time the more effective on microbes kill. For endoscopic equipment the biocide must contact with all lumens and channels. Presence of air pockets or incomplete immersion into biocide will cause failure of the disinfection.

7. Biofilms

    Biofilm is a group of microorganisms which are tightly stuck together onto a surface and cannot be easily removed. Microorganisms may protect themselves by producing biofilms.





See more information on these links:
1. Centers for Disease Control and Prevention
2. Queensland Health