Microbial control methods are used to prevent the spread of infectious agents, retard spoilage, and keep commercial products safe.

The population of microbes that cause spoilage or infection varies widely in species composition, resistance, and harmfulness. This means that microbial control methods must be adjusted to fit individual situations.

The type of microbial control is indicated by the terminology used. Sterilization and -cidal agents destroy all viable organisms, including viruses. Antisepsis, disinfection, sanitization, and -static agents reduce the numbers of viable microbes to a specified level.

An antiseptic agent is applied to living tissue to destroy or inhibit microbial growth.

A disinfectant agent is used on inanimate objects to destroy vegetative pathogens but not bacterial endospores.

Sanitization reduces microbial numbers on inanimate objects to safe levels by physical or chemical means.

Degermation refers to the process of mechanically removing microbes from the skin.

Microbial death is defined as the permanent loss of reproductive capability in microorganisms.

Antimicrobial agents attack specific cell sites to cause microbial death or damage. Any given antimicrobial attacks one of four major cell targets: 1. the cell wall, 2. the cell membrane, 3. biosynthesis pathways for DNA or RNA, 4. protein (enzyme) function.

Antimicrobials are described according to their ability to destroy or inhibit microbial growth. Microbicidal agents cause microbial death. They are described by what they are -cidal for: sporocides, bactericides, fungicides, viricides.

Methods of Physical Control
Physical methods of microbial control include heat, cold, pH, radiation, and drying.

Heat is the most widely used method of microbial control. It is used in combination with water, as dry heat, or as heat by flames (incineration).

The Thermal Death Time is the shortest length of time required to kill all microbes at a specific temperature. The TDT is longest for spore-forming bacteria and certain viruses.

The Thermal Death Point is the lowest temperature at which all microbes are killed in a specified length of time (10 minutes).

Autoclaving or steam sterilization is the process by which steam is heated under pressure to sterilize a wide range of materials in a comparatively short time (minutes to hours). It is effective for most materials except water-resistant substances such as oils, waxes, and powders.

Boiling water and pasteurization of beverages disinfect but do not sterilize materials.

Dry heat is microbicidal under specified times and temperatures. Flame heat, or incineration, is microbicidal. It is used when total destruction of microbes and materials is indicated.

Chilling, freezing, and desiccation are microbistatic but not microbicidal. They are NOT considered true disinfectants because they are not consistent in their effectiveness.

Ionizing radiation or cold sterilization by gamma and X rays is used to sterilize medical products, meats, and spices. It damages DNA and cell organelles by producing disruptive ions.

Ultraviolet light or non-ionizing radiation has limited penetrating ability. It is therefore restricted to disinfecting air and certain liquids.

Ultrasound is microbistatic to most microbes, but it is microbicidal to gram-negative bacteria. It is used primarily to reduce microbial load from inanimate objects.

Sterilization by filtration removes microbes from heat-sensitive liquids and circulating air. The pore size of the filter determines what kinds of microbes are removed.

Chemical Agents in Microbial Control
Chemical agents of microbial control are classified by their physical state and chemical nature.

Chemical agents can be either microbicidal or microbistatic. They are also classified as high-, medium-, or low-level germicides.

Factors which determine the effectiveness of a chemical agent include the type and numbers of microbes involved, the material involved, the strength of the agent, and the exposure time.

Halogens are effective chemical agents at both microbicidal and microbistatic levels. Chlorine compounds disinfect water, food, and industrial equipment. Iodine is used as either free iodine or iodophor to disinfect water and equipment. Iodophors are also used as antiseptic agents.

Phenols are strongly microbicidal agents used in general disinfection. Microbistatic phenol compounds, the bisphenols, are also used as antiseptics.

Alcohols dissolve membrane lipids and destroy cell proteins. Their action depends upon their concentration, but they are generally only microbistatic.

Surfactants are of two types: detergents and soaps. They reduce cell membrane surface tension, causing membrane rupture. Cationic detergents, or quats, can be weakly microbial, but they are limited by the amount of organic matter present and the microbial load.

Aldehydes are potent sterilizing agents and high-level disinfectants which irreversibly disrupt microbial enzymes.