Through the years, a growing terminology has emerged for describing and defining measures that control microbes. To complicate matters, the everyday use of some of these terms can at times be vague or inexact. For example, occasionally one may be directed to “sterilize” or “disinfect” a patient’s skin, even though this usage does not fit the technical definition of either term. To lay the groundwork for the coverage to follow, we present here a series of concepts, definitions, and usages in antimicrobial control.
Sterilization
Sterilization is a process that destroys or removes all viable microorganisms, including viruses. Any material that has been subjected to this process is said to be sterile. These terms should be used only in the strictest sense for methods that have been proved to sterilize. An object cannot be slightly sterile or almost sterile—it is either sterile or not sterile. Control methods that sterilize are generally re served for inanimate objects, because sterilizing tissues within a living body would call for such harsh treatment that it would be highly dangerous. As we shall see in chapter 13, many parts of the body—the brain and most internal organs, for example—are naturally free of microbes.
Sterilized products—surgical instruments, syringes, and some commercially packaged foods, just to name a few—are essential to hu man well-being. Although most sterilization is performed with a physical agent such as heat, a few chemicals called sterilants can be classified as sterilizing agents because of their ability to destroy spores.
At times, sterilization is neither practicable nor necessary, and only certain groups of microbes are of concern. Some antimicrobial agents eliminate only the susceptible vegetative states of microorganisms but do not destroy the more resistant endospore and cyst stages. Keep in mind that the destruction of spores is not always a necessity, because most of the infectious diseases of humans and animals are caused by non–spore-forming microbes.
Microbicidal Agents
The root -cide, meaning to kill, can be combined with other terms to define an antimicrobial agent aimed at destroying a certain group of microorganisms. For example, a bactericide is a chemical that destroys bacteria except for those in the endospore stage. It may or may not be effective on other microbial groups. A fungicide is a chemical that can kill fungal spores, hyphae, and yeasts. A virucide is any chemical known to inactivate viruses, especially on living tissue. A sporicidal agent can destroy bacterial endospores, which makes it also a sterilizing agent.
Agents that Cause Microbistasis
The words stasis and static mean to stand still. They can be used in combination with various prefixes to denote a condition termed microbistasis in which microbes are temporarily prevented from multiplying but are not killed outright. Although killing or permanently inactivating microorganisms is the usual goal of microbial control, microbistasis can have meaningful applications. Bacteriostatic agents prevent the growth of bacteria on tissues or on objects in the environment, and fungistatic chemicals inhibit fungal growth. Materials used to control microorganisms in the body (antiseptics and drugs) often have microbistatic effects because many microbicidal compounds are highly toxic to human cells.
Germicides, Disinfection, Antisepsis
A germicide, also called a microbicide, is any chemical agent that kills pathogenic microorganisms. A germicide can be used on in animate (nonliving) materials or on living tissue, but it ordinarily cannot kill resistant microbial cells. Any physical or chemical agent that kills “germs” is said to have germicidal properties.
The related term disinfection* refers to the use of a physical process or a chemical agent—a disinfectant—to destroy vegetative pathogens but not bacterial endospores. It is important to note that disinfectants are normally used only on inanimate objects because, at the concentrations required to be effective, they can be toxic to living tissue. Disinfection processes can also remove the harmful products of microorganisms (toxins) from materials. Examples of disinfection include applying a diluted solution of bleach to an ex amination table, exposing drinking water to UV radiation, and pasteurizing milk with heat.
In modern usage, sepsis is defined as the growth of microorganisms in the blood and other tissues. The term asepsis* refers to any practice that blocks the entry of infectious agents into sterile tissues and thus prevents infection. Aseptic techniques commonly practiced in health care range from sterile methods that exclude all microbes to antisepsis. With antisepsis, chemical agents called antiseptics are applied directly to exposed body surfaces (skin and mucous membranes), wounds, and surgical incisions to destroy or inhibit vegetative pathogens. Examples of antisepsis include pre paring the skin before surgical incisions with iodine compounds, swabbing a wound with hydrogen peroxide, and ordinary hand washing with a germicidal soap.
Methods that Reduce the Numbers of Microorganisms
Although medical applications quite often require sterility, especially with regard to invasive instruments such as scalpels, clamps, dental hand tools, and the like, in other situations this high level of microbial control is often unwarranted and perhaps even unwanted. In many cases it is more important to focus on reducing the size of a microbial population, or its microbial load. Sanitization refers to any cleansing technique that removes debris, soil, microorganisms, and toxins, and in this way reduces the potential for infection and spoilage. Soaps and detergents are the most commonly employed sanitizers. From a practical standpoint, sanitization can have an advantage over sterilization. For example, in a restaurant you could be given a sterile fork with someone else’s old food on it and a sterile glass with lipstick on the rim. Given that sanitization is in general far less expensive than sterilization, its cleansing effect has obvious advantages.
With living tissues, the reduction in microbial load through me chanical means is referred to as degermation. This process usually involves scrubbing the skin or immersing it in chemicals, or both. Microorganisms are removed both mechanically and indirectly by emulsifying the oils that coat the skin and provide a habitat for their growth. Examples of degerming procedures include the surgical handscrub, the application of alcohol wipes, and the cleansing of a wound with germicidal soap and water. Table 1 summarizes several of the important terms involved in microbial control.
Table1. Microbial Control Terminology
