Useful Notes on Pure Cultures of Microbe

Many microbiologists prefer to use the term “axenic” in order to avoid the misunderstanding that pure cultures are genetically pure. A pure, or axenic, culture is not genetically pure.

It is a population of microbes of the same species but may contain some individuals with mutations. Such genetically different individuals occur in populations of all kinds.

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However, this small degree of genetic variation does not usually interfere with the identification or understanding of species because the mutants are such a small portion of the group being studied.

Pure cultures are used in the laboratory to study several characteristics that identify and classify microbes. By placing cultures in various environments, microbiologists can identify the nutrients required for growth and the physical conditions that best suit the microbe.

These are called the cultural characteristics of the microbe. Microscopic examination of the microbes will reveal such traits as size, shape, cell arrangement, and motility.

These are morphological features. Very precise measurements of the nutrients used and wastes produced can be carried out with the cultures and identification of the metabolic characteristics can be made.

Killing the microbes, and fragmenting them is often done to separate their components, which in turn are analyzed to discover their chemical composition, unique differences among cell types (antigenic features), and genetic characteristics.

When all this information is combined, a very complete description and understanding of the microbe is obtained. However, there are drawbacks to the pure culture method.

No organism lives alone. Populations of organisms are constantly influenced by other populations in their environment. Their “typical” behaviour is, to a large extent, the result of various interactions with other species.

For example, animals that are isolated from others for long periods demonstrate “abnormal behaviour patterns”; some even become schizophrenic. The behaviour of microbes is also influenced by the presence of other species in their environment.

Limiting lab characterization and identification to pure culture methods provides very valuable information, but does not give a complete picture of the microbes as it “normally” functions in an environment of mixed species.

To overcome this problem and expand our understanding, new cultural methods are being developed called mixed culture techniques. By growing a number of different organism types in the same controlled laboratory environment, it is possible to simulate a “real-life” situation and obtain information that will help describe the microbe. Special tools and techniques are required to develop and maintain pure cultures of cultures of known mixtures.