CHARCOAL AGAR BASE

The genus Bordetella contains four species: Bordetella pertussis, Bordetella parapertussis, Bordetella bronchiseptica and Bordetella avium. Genetic studies have shown that these organisms are very closely related to each other. Humans are the only host of B.pertussis and B.parapertussis, while B.bronchoseptica is found in a wide variety of animals and occasionally found in humans. B.avium is found in birds. Bordetella species are obligately aerobic and metabolically not very active. They are non-motile except B. bronchoseptica. B.pertussis is the major cause of whooping cough or pertussis.
B.parapertussis is associated with a milder form of the disease. Primary isolation of B.pertussis in particular, requires the addition of charcoal, 15-20% blood to neutralize the growth-inhibiting effects. Isolation of this organism requires enrichment medium. Charcoal Agar is prepared according to the method of Mishulow, Sharpe and Cohen. This medium can be used as a replacement for Bordet-Gengou Agar for isolation of B. pertussis and for the production of B.pertussis vaccines. Charcoal Agar supplemented with horse blood can also be used for the cultivation and isolation of Haemophilus influenzae.
The difficulty in the isolation of Bordetella pertussis from nasopharyngeal secretions is the repression of unwanted flora during the long incubation period on nutritious media. Penicillin can be added to the medium as an antimicrobial agent for restricting the other contaminants. However, Penicillin resistant floras still cause contamination, which as observed by Lacey. Methicillin was found to be superior than Penicillin in suppressing unwanted nasopharyngeal flora as observed by Broome et al. Sutcliffe and Abbott found that Cephalexin was still better than Methicillin.
Examine plates after 40 hours of incubation and twice daily thereafter. Small shiny grayish white, round corner, colonies of Bordetella species are observed on plates. Confirm the findings with DFA i.e. Direct Fluorescent Antibody testing. To make earlier diagnosis, perform direct fluorescent antibody testing on the secretion.

for cultivation of fastidious microorganisms like Bordetella pertussis for vaccine production