Introduction to Microbial Control

Microbial Control Terminology

Decontamination is cleaning that renders an object safe to handle.

Disinfection is the elimination of virtually all recognized pathogenic microbes from objects.

Low Level -- Intended to destroy vegetative bacteria, most fungi and some viruses.

Intermediate Level -- Intended to destroy tubercle bacillus, all fungi and all viruses.

High Level -- Intended to destroy bacterial endospores.

Sterilization is the physical or chemical destruction of all microbial life on objects.

Antiseptics are germicides intended for use on skin or living tissue.

Disinfectants are germicides intended for use on inanimate objects.

Sterilants are germicides intended to completely sterilize an inanimate objects given sufficient contact time.

Mathematics of Sterilization

The probability of a given organism being killed during sterilization process is generally taken to be proportional to time with the proportionality constant dependent upon the process conditions. This results in the number of viable organisms decaying exponentially with exposure time. The rate of decay depends of the sensitive of the organism to the particular sterilization method. The initial number of organisms present is the referred to as the bioburden. These relationships are summarized in the equation:

where N_f is the final number of viable microbes present, N_i is the initial number of microbes present (the bioburden), t is the exposure time and 1/ D is the sensitivity of the microbes to the sterilization process. Values are D are species and condition dependent, but are sometimes specified as average values for a mixed culture.