Identification of Bacterial Unknowns

Citrate utilization

This is usually done on an agar slant. Organisms that are able to use citrate as a carbon source will turn the medium blue. Generally for enteric bacteria.

Hemolytic reactions

This test requires the use of a blood agar plate. For economy, try to run two organisms on a half-plate each. Streak or swab for moderate growth, and incubate overnight. There are two types of reaction: a hemolysis is due to the production of H2O2 and produces a greenish area around the colonies; b hemolysis is due to the lysis of the red blood cells and results in an area of clearing around the colonies. No change in the medium around the colonies indicates no hemolysis, sometimes called g hemolysis.


Remember that these are living organisms, and not always 100% predictable. It is by the preponderance of the evidence that they are identified. Be aware that they will, from time to time, show phenotypic traits that supposedly they don't have.