Unit 6.1: Control of Bacterial Growth
Outline
Physical Methods of Microbial Control
Learning Objectives
After reading the following, you should be able to:
- Define: sterilization, sterile, commercially sterile, disinfection, disinfectant, bactericide, bacteriostatic, sanitization, antiseptic, aseptic, degerming.
- Describe how the efficiency of anti-microbial agents (AMA) is expressed.
- Describe the factors that can affect the effectiveness of a particular antimicrobial agent.
- Explain the two general, modes of action of antimicrobial agents.
- Describe and explain specific physical and chemical methods used to control microbial growth based on application.
- Be able to identify which methods are more effective for specific types of microbes.
How clean is clean? People wash their cars and vacuum the carpets, but most would not want to eat from these surfaces. Similarly, we might eat with silverware cleaned in a dishwasher, but we could not use the same dishwasher to clean surgical instruments. As these examples illustrate, “clean” is a relative term. Car washing, vacuuming, and dishwashing all reduce the microbial load on the items treated, thus making them “cleaner.” But whether they are “clean enough” depends on their intended use. Because people do not normally eat from cars or carpets, these items do not require the same level of cleanliness that silverware does. Likewise, because silverware is not used for invasive surgery, these utensils do not require the same level of cleanliness as surgical equipment, which requires sterilization to prevent infection.
Why not play it safe and sterilize everything? Sterilizing everything we come in contact with is impractical, as well as potentially dangerous. As this chapter will demonstrate, sterilization protocols often require time- and labor-intensive treatments that may degrade the quality of the item being treated or have toxic effects on users. Therefore, the user must consider the item’s intended application when choosing a cleaning method to ensure that it is “clean enough” (Figure 6.1)
To prevent the spread of human disease, it is necessary to control the growth and abundance of microbes in or on various items frequently used by humans. Inanimate items, such as doorknobs, toys, or towels, which may harbor microbes and aid in disease transmission, are called fomites. Two factors heavily influence the level of cleanliness required for a particular fomite and, hence, the protocol chosen to achieve this level. The first factor is the application for which the item will be used. For example, invasive applications that require insertion into the human body require a much higher level of cleanliness than applications that do not. The second factor is the level of resistance to antimicrobial treatment by potential pathogens. For example, foods preserved by canning often become contaminated with the bacterium Clostridium botulinum, which produces the neurotoxin that causes botulism. Because C. botuli