Selective medium for isolation of Haemophilus somnus from cattle and sheep
Slee, K.J.; Stephens, L.R.
Veterinary Record 116(8): 215-217
1985
ISSN/ISBN: 0042-4900 PMID: 3984199 Document Number: 261199
Incorporation of vancomycin (5 micro g/ml), neomycin (5 micro g/ml), sodium azide (50 micro g/ml), nystatin (100 iu/ml) and cyclohexamide (100 micro g/ml) into 5% horse blood agar resulted in a selective medium for the primary isolation of H. somnus from cattle and sheep. Addition of thiamine monophosphate (1 micro g/ml) to the medium enhanced growth of this bacterium. Gram-positive bacteria did not grow on the medium, and colonies of many Gram-negative bacteria were eliminated or reduced in numbers and size. Colonies of H. somnus were larger on the selective medium than on sheep blood agar but retained typical morphology. Recovery of 18 laboratory strains was 73-166% (mean 112) on sective medium compared to sheep blood agar. H. somnus was isolated from the vagina of 136 (28.6%) of 476 cows surveyed, 79 (16.6%) on sheep blood agar and 129 (27.1%) on selective medium. The selective agents and thiamine were stable indefinitely as a freeze dried mixture, while prepared plates were stable for two weeks.