What are Pure Culture Techniques?

Microorganisms can be isolated from various natural environments like soil, food, water, sewage, decomposing matter and even from infectious materials such as pus, sputum, urine etc. These sources usually contain a mixed population of microorganisms containing several species in close association with one another. This mixed population, however, pose a problem for microbiologists as a pure culture (a culture containing only a single kind of microorganisms) is required for studying a particular species.

Different characteristics of a microbe like colony appearance, morphological, physiological, biochemical and immunological characteristics or antimicrobial susceptibility can be studied adequately only in a pure culture. Pure culture can be defined as a population of cells arising from a single cell. Both conventional and more advanced approaches can be used to prepare pure cultures. These are - (1) Plating Method, (2) Agar Shake Tube Method, (3) Most Probable Number (MPN) Method, and (4) Laser Tweezer Technology.

All these methods involve two operations:

(i) isolation of a particular microorganism from a mixed population, and

(ii) cultivation of the isolated microorganism on culture media. Let us get to know about these methods. We begin with the most common one - the plating method.