Short series of biochemical tests

We identify intestinal bacteria (within the Enterobacteriaceae family) on the basis of the biochemical properties of individual genera. We use a short series of biochemical reactions for this. It is a series of test tubes in which various biochemical tests are performed. The summary of results is always characteristic of a certain gender. Tests include: fermentation glucose, H2S formation, urease formation, Simmons citrate, and indole formation.

Glucose fermentation + gas formation

 * Glucose solution with bromothymol blue + gas
 * Principle: the reaction uses pH changes during fermentation of sugars + the gas is in the test tube upside down, if the bacteria produce gas, they accumulate in it and form a bubble.
 * Result:
 *  Positive with bubble  - yellow (glucose fermentation) + bubble;
 *  positive without bubble  - yellow (glucose fermentation)
 *  negative  - green-blue (no fermentation).

H2S formation

 * Hajny soil (ferric ammonium citrate indicator)
 * Principle: lead sulphide elimination causes soil blackening.
 * Result:
 *  positive  - blackening;
 *  negative  - red, yellow.

Urease formation

 * Soil with urea
 * Principle: urease produced by bacteria breaks down urea in the soil, alkalises the environment and pinks the soil.
 * Result:
 *  positive:  soil flushing;
 *  negative:  green, yellow.

Simmons citrate

 * Soil with sodium citrate and bromothymol blue as an indicator
 * Principle:  bacteria use sodium citrate as a carbon source, ammonia is released, this leads to alkalisation of the environment and bluing of the soil
 * Result:
 *  positive:  soil bluing;
 *  negative:  green, yellow.

Indole formation

 * Hottinger broth (contains tryptophan) + Ehrlich (paradimethylaminobenzaldehyde) or Kovács reagent
 * Principle: tryptophan is formed by the action of indole bacteria, the presence of which can be demonstrated by the addition of an agent.
 * Result:
 *  positive:  red ring on the surface;
 *  negative:  yellow ring.

== Resolution of the most important bacteria ==
 * fermentation with gas formation ... +g
 * fermentation without gas formation ... +
 * negative reactions ...-
 * different results ... r

Related Articles

 * Bacitracin test
 * CAMP test
 * E-test
 * Catalase test
 * Optoquine test
 * Plasma coagulase test

Used literature

 * BEDNÁŘ, M, V FRAŇKOVÁ a J SCHINDLER, et al. Lékařská mikrobiologie – bakteriologie, virologie, parazitologie. 1. vydání. Praha : Marvil, 1996. 558 s.  ISBN 80-238-0297-6.


 * ŠMÍROVÁ, Václava. Úvod do lékařské mikrobiologie. - edition. -.


 * -Praktika 2. LF [online]. [cit. 2011-12-16]. .