[Use of selective nutrient media for isolating the streptococci that cause mastitis]

Studied was the diagnostic value of the liquid enriched nutrient medium - Streptococcus broth with kanamycin, used for the isolation of Sc. agalactiae and other mastitis streptococci in individual milk samples as well as that of blood dextrose agar with polymyxin + Staphylococcus toxin seeded after Koch for the isolation of Sc. agalactiae and other hemolytic streptococci in pooled cow milk. Direct seedings in thallium sulfate-crystal violet-B toxin blood agar (TKT agar) were used as a control. It was found that the enriched Streptococcus broth with kanamycin yields growth of 0.23 per cent more Sc. agalactiae organisms and 1.82 per cent other mastitis streptococci in individual milk samples as compared to the TKT agar. The blood dextrose agar with polymyxin seeded after Koch demonstrates fivefold more Sc. agalactiae in pooled cow milk as against the direct seedings in TKT agar, and it can be used to confirm the infection on the farms.