Closely related organisms can be differentiated using a series of biochemical tests that identify various metabolic properties of different bacterial species.
Table 1:Examples of biochemical tests used to identify bacteria
| Biochemical Test | Function | |
|---|---|---|
| 能动性 | Identifies the bacteria's ability to move (flagellated cell). | |
| Oxidase | Demonstrates the bacteria's ability to produce cytochrome-c oxidase, hence the capability of reducing oxygen. | |
| Glucose Fermentation | Determines the ability of a bacterium to ferment the sugar glucose, and to convert pyruvic acid into gaseous by products. | |
| Nitrate | Determines the ability of a bacterium to produce the enzyme nitratase, hence its capability of converting nitrate into nitrite | |
| Fluid Thioglycollate | Shows oxygen usage. | |
| Urea | Determines the ability of a bacterium to produce the enzyme urease, hence its capability of hydrolyzing urea. | |
| 胰蛋白胨肉汤/吲哚 | Determines the ability of a bacterium to produce the enzyme tryptophanase. | |
| MR-Methyl Red | Indicator of low pH. Determines the fermentation ability of bacteria. | |
| VP- Voges Proskauer | Determines the ability of a bacterium to produce acetoin. | |
| Simmons citrate slant | Demonstrates the ability of Gram-negative bacteria to use citrate as an energy source. |
Specialized media exists that combines different biochemical identification methods to specifically identify certain genus of bacteria. For example, the沙门氏菌Shigella agarenables scientist to efficiently test a sample for沙门氏菌contamination.
The main drawback of biochemical identification methods is they can only be used for organisms that can be cultivatedin vitro。如果一个microorganism cannot be cultivated,molecular methodshave to be used for identification.