Culturing technique is used for the propagation of microorganisms in the microbiology laboratory; and it is an important procedure required for studying the morphological characteristics of microbes especially on solid culture media. Microorganisms are cultured in various ways and in various conditions using different growth media (inclusive of solid media or broth/liquid media).
Bacterial growth on solid culture media is often the best approach for studying the physical appearance of a microbe in terms of its consistency, shape, texture, size and colour amongst other colonial features of microbes on solid growth medium. Culturing technique involves the inoculation of growth media with the inoculum (e.g. bacteria or fungi) or test sample suspected to contain a particular microbe.
The incubation of the culture plate under optimum condition that encourage the growth of the test organism. The cultured organism can appear in any of these forms on the solid culture media: as individual or discrete colonies and as confluent growth (i.e. film of surface growth).
Confluent growth is often required for performing antimicrobial susceptibility testing in the microbiology laboratory. In broth or liquid medium, bacterial growth is usually inferred by the presence of turbidity or cloudiness in the medium; and a loopful of the organism can be transferred onto a solid culture media to obtain pure cultures.
Various culturing techniques are used for the propagation of microorganisms in the microbiology laboratory. Examples of some notable culturing procedure include stab culture (produced by deep inoculation of solid medium in a tube with a straight wire loop), slope or slant culture (produced on the gradient of a solid medium in tubes) and plate culture (Figure 1) amongst others.
Figure 1. A nutrient agar culture plate. The organism is a clinical isolate of Klebsiella pneumoniae.
Note: Stab cultures are often used for biochemical tests and mycological investigations in which fungi or fungal samples are stabbed deep into solid media in tubes.
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