Effect of antibiotics on staphylococcal hemolysin production.

Thirty-seven per cent of 126 strains of Staphylococcus aureus, when tested on sheep blood-agar with sensitivity discs containing cephalothin, carbenicillin, oxacillin, penicillin, and cycloserine, produced rings of beta-hemolysis surrounding zones of inhibition of bacterial growth. Each strain capable of producing a ring of beta-hemolysis did so with at least two of the mentioned antibiotics. None of the other 15 antibiotics tested was associated with a ring of beta-hemolysis surrounding any of the zones of inhibition. It appears, therefore, that the beta-hemolysis observed was produced by certain strains of S. aureus only in association with certain antibiotics.