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Chapter: Microbiology and Immunology: Sterilizationand Disinfection

Definition of Frequently Used Terms in Sterilizationand Disinfection

Sterilization is defined as a process by which an article, sur-face, or medium is freed of all living microorganisms either in the vegetative or in the spore state.

Definition of Frequently Used Terms

Sterilization is defined as a process by which an article, sur-face, or medium is freed of all living microorganisms either in the vegetative or in the spore state. Any material that has been subjected to this process is said to be sterile. These terms should be used only in the absolute sense. An object cannot be slightly sterile or almost sterile; it is either sterile or not sterile. 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.

A germicide, also called a microbicide, is any chemical agent that kills pathogenic microorganisms. A germicide can be used on inanimate (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.

Disinfection refers to the use of a chemical agent thatdestroys or removes all pathogenic organisms or organisms capable of giving rise to infection. This process destroys vegeta-tive pathogens but not bacterial endospores. It is important to note that disinfectants are normally used only on inanimate objects because they can be toxic to human and other animal tissue, when used in higher concentrations. Disinfection pro-cesses also remove the harmful products of microorganisms (toxins) from materials. Examples of disinfection include (a) applying a solution of 5% bleach to examining table, (b) boil-ing food utensils used by a sick person, and (c) immersing ther-mometers in an isopropyl alcohol solution between use.

In modern usage, sepsis is defined as the growth of micro-organisms in the body or the presence of microbial toxins in blood and other tissues. The term asepsis refers to any practice that prevents the entry of infectious agents into sterile tissues and thus prevents infection.

     Chemical agents called antiseptics are applied directly to the exposed body surfaces (e.g., skin and mucous membranes), wounds, and surgical incisions to destroy or inhibit vegetative pathogens. Examples of antisepsis include (a) preparing the skin before surgical incisions with iodine compounds, (b) swabbing an open root canal with hydrogen peroxide, and (c) ordinary hand washing with a germicidal soap.

Sanitization is any cleansing technique that mechanicallyremoves microorganisms (along with food debris) to reduce the level of contaminants. A sanitizer is a compound (e.g., soap or detergent) that is used to perform this task. Cooking utensils, dishes, bottles, cans, and used clothing that have been washed and dried may not be completely free of microbes, but they are considered safe for normal use. Air sanitization with ultraviolet lamps reduces airborne microbes in hospital rooms, veterinary clinics, and laboratory installations.

It is often necessary to reduce the numbers of microbes on the human skin through degerming procedures. This process usually involves scrubbing the skin or immersing it in chemi-cals, or both. It also emulsifies oils that lie on the outer cutane-ous layer and mechanically removes potential pathogens from the outer layers of the skin. Examples of degerming procedures are (a) surgical hand scrub, (b) application of alcohol wipes to the skin, and (c) cleansing of a wound with germicidal soap and water. The concepts of antisepsis and degerming procedures clearly overlap, since a degerming procedure can be simultane-ously treated as an antiseptic and vice versa.


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