Approaches to Control

The processes used to control microorganisms are either physical or chemical, though a combination of both may be used. Physical methods include heat treatment, irradiation, filtration, and mechanical removal (washing). Chemical methods use any one of a variety of antimicrobial chemicals. The method chosen depends on the circumstances and resulting degree of control required.

Definitions related to microbial control are summarized in table 5.1.

Principles of Control

The process of removing or destroying all microorganisms and viruses on or in a product is called sterilization. These procedures

Chapter 5 Control of Microbial Growth

Table 5.1 Terms Commonly Used to Describe Antimicrobial Agents and Processes




A disinfectant that is non-toxic enough to be used on skin.

Aseptic technique

Use of specific methods to exclude contaminating microorganisms from an environment.


Kills bacteria.


Prevents the growth of, but does not kill, bacteria.


Treatment used to reduce the number of disease-causing microbes to a level that is considered safe to handle.


Treatment used to decrease the number of microbes in an area.


A chemical used to destroy many microorganisms and viruses.


A process that eliminates most or all disease-causing microorganisms and viruses on or in a product.


Kills fungi.


Kills microorganisms and inactivates viruses.


A brief heat treatment used to reduce the number of spoilage organisms and to kill disease-causing microbes.


The process of inhibiting the growth of microorganisms in products to delay spoilage.


To reduce the number of microorganisms to a level that meets public health standards; implies cleanliness as well.


A chemical used to destroy all microorganisms and viruses in a product, rendering it sterile.


Completely free of all microorganisms and viruses; an absolute term.


The process of destroying or removing all microorganisms and viruses, through physical or chemical means.


Inactivates viruses.

include removing microbes by filtration, or destroying them using heat, certain chemicals, or irradiation. Destruction of microorganisms means they cannot be "revived" to multiply even when transferred from the sterilized product to an ideal growth medium. A sterile item is one that is absolutely free of microbes, including endospores and viruses. It is important to note, however, that the term sterile does not encompass prions. These infectious protein particles are not destroyed by standard sterilization procedures. ■ endospores, p. 67 ■ prions, p. 365

Disinfection is the process that eliminates most or all disease-causing microorganisms and viruses on or in a material. Unlike sterilization, disinfection suggests that some viable microbes may persist. In practice, the term disinfection generally implies the use of antimicrobial chemicals. Those used for disinfecting inanimate objects are called disinfectants. Disinfectants are biocides (bio means "life," and cida means "to kill"). Although they are at least somewhat toxic to many forms of life, they are typically used in quantities and concentrations that target microscopic organisms, including bacteria and their endospores, fungi, and viruses. Thus, they are often called germicides. When disinfectants are formulated for use on skin they are called antiseptics. Antiseptics are routinely used to decrease the number of bacteria on skin to prepare for invasive procedures such as surgery.

Pasteurization uses a brief heat treatment to reduce the number of spoilage organisms and kill disease-causing organisms. Foods and inanimate objects can be pasteurized.

The term decontaminated is used to describe an item that has been treated to reduce the number of disease-causing organisms to a level that it is considered safe to handle. The treatment may be as simple as thorough washing, or it may involve the use of heat or disinfectants.

Sanitized generally implies a substantially reduced micro-bial population that meets accepted health standards. Most people also expect a sanitized object to be clean in appearance. Note that this term does not denote any specific level of control.

Preservation is the process of delaying spoilage of foods or other perishable products by adding growth-inhibiting ingredients or adjusting storage conditions to impede growth of microorganisms.

Situational Considerations

Methods used to control microbial growth vary greatly depending on the situation and degree of control required (figure 5.1). Control measures adequate for routine circumstances of daily life might not be sufficient for situations such as hospitals, microbiology laboratories, foods and food production facilities, and other industries.

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