Differentiation of Pasteurella haemolytica biotypes A and T with growth inhibitors.

Differentiation of type A and type T cultures of Pasteurella haemolytica was accomplished by paper disks containing 0.3 microgram of penicillin G, which produced zones of inhibition larger than 10 mm with type A but not with type T strains. Basic fuchsin (0.2 microgram/ml), brilliant green (0.005 microgram/ml), methylene blue (3.1 micrograms/ml) in brain heart infusion broth permitted the growth of type T but that of type A isolates.