Tests Used in the Identification of Bacteria

Bacteria are among the most numerous and diverse group of organisms on the planet. Determinative bacteriology employs a number of nutritional and biochemical tests to identify bacteria. Traditionally, these methods have often required extensive time to culture, isolate and test the bacteria. However, recent technological advances have allowed rapid detection methods to be developed.

Staining

• The Gram stain is frequently employed as an initial step in bacterial identification and uses a stain, decolorizer, and counterstain to identify bacteria according to their cell wall. Other staining methods include acid-fast staining, spore staining and negative staining.

Cell Morphology

• When viewed under the microscope, bacteria may be categorized according to the shape of their cells. These shapes include bacilli (rod-shaped) bacteria cells and cocci (spherical-shaped bacteria cells).

Nutrient Agar

• Bacteria are often simultaneously on multiple agar dishes each containing varying nutrients. Bacteria can be further segregated by the nutrients required for growth, colony morphology, and in some cases, substances which inhibit growth.

Biochemical Tests

• The reaction of bacteria to certain substances can aid in identification. For example, a catalase test detects the presence of the catalase enzyme by adding hydrogen peroxide and observing for the formation of oxygen bubbles.

Serological

• Antibodies may be used to detect very specific proteins on a bacterium. This has enable the development of agglutination tests, ELISA (enzyme-linked immunosorbent assay) and the Western Blot.

DNA

• Increasingly, methods are being developed and employed which allow bacteria to be identified according to genetic markers within their genome. These methods allow for much quicker identification and a substantial amount of automation to bacterial identification.