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Biology LibreTexts

6.15A: Effective Disinfection

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    9219
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    A perfect disinfectant would offer full microbiological sterilisation, without harming humans and would also be non-corrosive.

    LEARNING OBJECTIVES

    Describe the rationale for selecting a disinfectant and how their effectiveness is rated

    KEY TAKEAWAYS

    Key Points

    • Most modern household disinfectants contain Bitrex, an exceptionally bitter substance added to discourage ingestion, as a safety measure.
    • The choice of disinfectant to be used depends on the particular situation.
    • One way to compare disinfectants is to compare how well they do against a known disinfectant, such as phenol, and rate them accordingly.

    Key Terms

    • non-corrosive: That does not cause corrosion.
    • disinfectant: A substance which kills germs and/or viruses.
    • sterilisation: Sterilization (or sterilisation) is a term referring to any process that eliminates (removes) or kills all forms of microbial life, including transmissible agents (such as fungi, bacteria, viruses, spore forms, etc.) present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media.

    A perfect disinfectant would also offer complete and full microbiological sterilisation, without harming humans and useful forms of life. It would also be inexpensive and non-corrosive. Most disinfectants, however, are by nature, potentially harmful (even toxic) to humans or animals. Most modern household disinfectants contain Bitrex, an exceptionally bitter substance added to discourage ingestion, as a safety measure. Those that are used indoors should never be mixed with other cleaning products, or else chemical reactions can occur.

    The choice of disinfectant depends on the particular situation. Some disinfectants have a wide spectrum and kill many different types of microorganisms, while others kill a smaller range of disease-causing organisms but are preferred for other instances (they may be non-corrosive, non-toxic, or inexpensive).

    There are arguments for creating or maintaining conditions that are not conducive to bacterial survival and multiplication, rather than attempting to kill them with chemicals. Bacteria can increase in number very quickly, which enables them to evolve rapidly. Should some bacteria survive a chemical attack, they give rise to new generations composed completely of bacteria that are resistant to the particular chemical used. Under a sustained chemical attack, the surviving bacteria in successive generations are increasingly resistant to the chemical used, and ultimately the chemical is rendered ineffective. For this reason, some question the wisdom of impregnating cloths, cutting boards, and worktops in the home with bactericidal chemicals.

    image

    Disinfection: Disinfection of a floor using disinfectant liquid applied using a mop

    One way to compare disinfectants is to compare how well they do against a known disinfectant and rate them accordingly. Phenol is the standard disinfectant, and the corresponding rating system is called the “phenol coefficient. ” The disinfectant to be tested is compared with phenol on a standard microbe (usually Salmonella typhi or Staphylococcus aureus). Disinfectants that are more effective than phenol have a coefficient > 1. Those that are less effective have a coefficient < 1.

    A less specific measurement of effectiveness is the United States Environmental Protection Agency’s (EPA) classification into either high, intermediate, or low level of disinfection. High-level disinfection kills all organisms, except high levels of bacterial spores, and is effected with a chemical germicide cleared for marketing as a sterilant by the U.S. Food and Drug Administration (FDA). Intermediate-level disinfection kills mycobacteria, most viruses, and bacteria with a chemical germicide registered as a “tuberculocide” by the EPA. Low-level disinfection kills some viruses and bacteria with a chemical germicide registered as a hospital disinfectant by the EPA.