microbiology Microbiology () is the branches of science, scientific study of microorganisms, those being of unicellular organism, unicellular (single-celled), multicellular organism, multicellular (consisting of complex cells), or non-cellular life, acellula ...

, in the context of a

sterilization Sterilization may refer to: * Sterilization (microbiology), killing or inactivation of micro-organisms * Soil steam sterilization, a farming technique that sterilizes soil with steam in open fields or greenhouses * Sterilization (medicine) render ...

procedure, the D-value or decimal reduction time (or decimal reduction dose) is the time (or dose of an

antimicrobial drug An antimicrobial is an agent that kills microorganisms (microbicide) or stops their growth (bacteriostatic agent). Antimicrobial medicines can be grouped according to the microorganisms they are used to treat. For example, antibiotics are used aga ...

) required, at a given condition (e.g.

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

) or set of conditions, to achieve a one-

log reduction Log reduction is a measure of how thoroughly a decontamination process reduces the concentration of a contaminant. It is defined as the common logarithm of the ratio of the levels of contamination before and after the process, so an increment of ...

, that is, to kill 90% of relevant

microorganisms A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

. A D-value is denoted with the capital letter "D". Thus, after an exposure time of 1 D, only 10% of the organisms originally present in a

microbial colony In biology, a colony is composed of two or more conspecific individuals living in close association with, or connected to, one another. This association is usually for mutual benefit such as stronger defense or the ability to attack bigger prey ...

would remain. The term originated in assessments of microbes' thermal resistance and in

thermal death time Thermal death time is how long it takes to kill a specific bacterium at a specific temperature. It was originally developed for food canning and has found applications in cosmetics, producing salmonella-free feeds for animals (e.g. poultry) and pha ...

analysis; however, it now has analogous uses in other microbial resistance and death rate applications, such as for

ethylene oxide Ethylene oxide is an organic compound with the chemical formula, formula . It is a cyclic ether and the simplest epoxide: a three-membered ring (chemistry), ring consisting of one oxygen atom and two carbon atoms. Ethylene oxide is a colorless ...

and

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

processing.

Details

Use of D-values is based on the assumption that the procedure in question causes the number of living microorganisms to decay exponentially. From this perspective, D-values can be understood as roughly analogous to

half lives Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * '' Half Life: A Parable for t ...

of radioactive substances, however a half life involves a reduction of 50% rather than 90%. The half life is actually roughly 30% () of the D-value, so if D = 10 minutes, the number of living microorganisms will be halved in about 3 minutes. Generally, each lot of a

-resistant organism will have its own specific D-value. Determining a D-value requires an experiment, but only gives the D-value under the specific conditions of that experiment. D-values are unique to the conditions of the environment that the bacteria currently exists in. In the context of thermal analysis it is typical practice to subscript the "D" with an indication of temperature. For example, given a hypothetical organism which is reduced by 90% after exposure to temperatures of 150° C for 20 minutes, the D-value would be written as D_150C = 20 minutes. In the US, the temperature is usually indicated in

degrees Fahrenheit The Fahrenheit scale () is a temperature scale based on one proposed in 1724 by the German-Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he original ...

; a notation like D₂₃₀ should be understood to mean D_230F (D_110C). When describing D-value generally for any temperature, like in the heading of a table, a common abbreviation is D_''T'' (where ''T'' stands for the temperature), where specific values for ''T'' may be given elsewhere. A numeric subscript may also be used to indicate some other level of reduction than 90%; for example, D₁₀ denotes the time required for a 10% reduction. D-values are sometimes used to express a

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than ...

's efficiency in reducing the number of microbes present in a given environment.

References

{{reflist Microbiology

Details

See also

References