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Veterinary bacteriology: information about important bacteria
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Hematin agar (= Chocolate agar)

Chocolate agar

The figure shows a hematin agar plate on which bacteria have not been cultivated. Note the colour, which is more brownish than ordinary blood agar plates or FAA plates. - Click on the image to enlarge it.

Image: Karl-Erik Johansson (BVF, SLU) and Lise-Lotte Fernström (BVF, SLU).


Hematin agar , which is also called chocolate blood agar or simply chocolate agar, is a non-selective enrichment medium. This medium is used for isolation of fastidious bacteria as for instance Haemophilus spp. and Taylorella equigenitalis.

The medium contains:

  • 10% fresh sheep blood
  • beef extract (contains nutrients)
  • peptone
  • NaCl
  • agar (gelifying agent)
  • H2O

The pH of the medium should be 6,8. Hematin agar has basically the same composition as blood agar, but hematin agar is heated in a boiling water bath for 1 h until the colour has changed from red to chocolate brown.

Other comments:

When the blood has been heated as above, are the red blood cells lysed and hemin (X-factor) and NAD (V-factor) have been released. These substances are essential nutrients for some bacteria. The name chocolate agar is referring to the color of the medium and not to its content. Hemolysis cannot be observed on hematin agar. By adding some substances, the medium can be more selective.

Updated: 2018-05-09.


New names of taxa within the classification category phylum

During October 2021, an article was published by A. Oren och G.M. Garrity, in which new names are proposed for a number of taxa within the classification category phylum. This has resulted in many discussions in social media about whether it was really necessary to make these changes, which have created confusion among microbiologists and other professionals who come into contact with bacteriology.

Published 2022-09-28. Read more...

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