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 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.
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.