Question

How are metabolic capabilities used to phenotypically identify microbes?

Answer 1

Bacterial metabolic capabilities are used to identify the type of microbe. General biochemical test are used to distinguish microbes.

For example,

1. Citrate test: Used to identify those bacteria which can use citrate as a carbon source. Some bacteria uses only citrate as a carbon source.

Eg., Citrobacter freundii.

2. Hippurate test: this test is used to identify those bacteria which can convert hippurate to glycine.

Eg., Campylobacter jejuni

3. Indole test: this test is used to identify those bacteria which can hydrolyze tryptophan to indole and pyruvic acid.

Eg.,

4. Lecithinase test: used to identify those bacteria which can cleave phospholipids.

Eg., Bacillus cereus

5. Voges-Proskauer (VP) test: used to identify those bacteria which can ferment butanediol.

Eg., Klebsiella spp.

6. Litmus milk decolorization test: used to identify those bacteria which can metabolize milk.

Eg., Enterococcus spp.

7. Carbohydrate fermentation test: different types of carbohydrates used by different types of bacteria. This is identified by simple pH indicator based test in which phenol red is used as a pH indicator. In addition gas production during fermentation of few carbohydrates is also used as an indicator. For such studies special tubes are used known as Durham tubes.