Step in systematic bacteriology



Bacterial identification step

The first rule in bacterial identification is that the organism must be in pure culture. A single representative colony is peak and subculture for purity and identification test are done in from the purify culture. If the culture is not pure the test are not valid.

Colonial morphology

Usually with the careful observations of the colonial morphology of the organism and experience bacteriology may know or have a good idea of the likely identity of the bacterium. Reaction on differential medium may be helpful eg lactose fermenting or non lactose fermenting colonies; hemolytic action or non hemolytic action on blood agar. The presence of pigmentation is also taken into account. The practice of sniffing the cultures to determine any specific order is now frown upon as bad laboratory practice for safety reason. However the characteristic order of some bacteria is a useful diagnostic a guide.

Gram stain

Gram stain is a very useful procedure in systematic bacteriology. For beginner or an inexperienced laboratory scientist the first step in the arduous task of bacteriological identification is a gram stain. The gram staining techniques must be properly mastered. A badly stained smear can be very misleading. For example under decolored gram negative bacilli become gram positive why over coalored gram positive cocci will be read as gram negative cocci. If the first step is wrong the choice of subsequent test may be wrong. Gram stain when properly done is a very useful guide in initiation of test required for identification and isolation of a bacteria. Gram staining reactions will usually points to the next set of tests to be done. It is a rule not to name or identify any bacteria by the gram staining result especially for a beginner. The morphology of staining bacteria in many cases not definitive. Even a train I sometimes get confused by the shape and size of the stained bacteria. However and experience hand who for example recognise lactose fermenting colony may not need to do a gram stain you can confidently go on with the other test.

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Biochemical test

Gram staining result determine the types of biochemical test to be done. This test can be in the form of any of the various identification systems such as API.

Serological test

From the result of the biochemical reaction the identifier of some bacteria species may need to be confirmed with a serological test. This is true if enteric pathogens such as salmonella and shigella species is identified.

Guideline of bacteria identification

The laboratory should be kept among its reference books reference identification manual. It is most helpful where full identifications of a bacterial isolate is carried out on a daily basis. the bench bacteriology is usually has a feeling of satisfaction when he successfully identified a bacterium especially if it is one of the rare organism.

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Systematic bacteriology is the core of the work of a clinical bacteriology laboratory. It require patient and perseverance. It keep the battery allergies on the alert to always remember some specific reactions of certain bacteria. With a constant renaming of bacteria the laboratory scientist who is involved in systematic bacteriology is left less confused than other.

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medical laboratory science theory and practical

J. Ochei

A. Kolhatkar


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