CASMAN AGAR

Description

Fastidious microorganisms such as Haemophilus and Neisseria require the addition of X and V- growth factors for in vitro cultivation. Casman described a blood-enriched medium for cultivation of Haemophilus and gonococci. The medium was developed to replace the previously described formulations that required time-consuming preparations using fresh and heated blood and meat infusion to supply the essential nutrients for growth of these fastidious organisms. Blood supplies factor-X (hemin) and factor-V (Nicotinamide Adenine Dinucleotide), which is required for growth of Haemophilus influenzae. Sheep blood lacks factor-V due to NADase, an enzyme that destroys factor- V. Horse and rabbit blood supplies both the factor X and factor V, and are relatively free of NADase activity, therefore it is preferred over sheep blood. Nicotinamide is added to medium to inhibit nucleotidase of erythrocytes that may destroy factor V. Inoculate the medium as soon as the specimen arrives at the laboratory. After incubation H. influenzae produces colourless to grey colonies with a characteristic mousy odour while N. gonorrhoeae produces small colourless to greyish-white colonies.