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 genus. Tests include: fermentation of 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 medium (ferric ammonium citrate indicator)
 * Principle: lead sulfide elimination causes medium blackening.
 * Result:
 *  positive  - blackening
 *  negative  - red, yellow

Urease formation

 * Medium with urea
 * Principle: urease produced by bacteria breaks down urea in the medium, which leads to an increase in pH and the medium turns pink.
 * Result:
 *  positive:  medium color change
 *  negative:  green, yellow

Simmons citrate

 * medium with sodium citrate and bromothymol blue as an indicator
 * Principle:  bacteria use sodium citrate as a carbon source, ammonia is released, this leads to the increase in the pH of the environment and bluing of the medium
 * Result:
 *  positive:  medium bluing
 *  negative:  green, yellow

Indole formation

 * Hottinger broth (contains tryptophan) + Ehrlich (paradimethylaminobenzaldehyde) or Kovács reagent
 * Principle: tryptophan is degraded by some bacteria, producing indole (indole-positive 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: -
 * differing results: r

Related Articles

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

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]. .