[Effect of antibiotics on hemolysin production by bacteria causing mastitis in cattle]

Effect of six antibiotics on the hemolysin formation by 320 strains of Staphylococcus (including 112 S. aureus) and 100 strains of S. agalactiae isolated from cow udders, have been determined. Tests were performed on plates containing 5% horse red cells, but the hemolytic strains were tested on blood agar plates supplemented with 5% sheep, rabbit and calf cells in addition. One strain of S. aureus produced the rings of hemolysis around the zones of growth inhibition on the media containing the discs of penicillin, erythromycin, oxyterramycin and chloramphenicol. Another strain of S. agalactiae produced similar rings, but only on the medium supplemented with penicillin. On the calf blood agar plate, S. aureus produced the hemolytic rings only in association with streptomycin and neomycin. After five times of propagation on the nutrient agar, the hemolytic phenomenon was not reproducible. It may be suggested that in cow milk there are some inhibitors for hemolysin formation by Staphylococcus and S. agalactiae.