Staphylococcal antagonism to penicillin-G therapy of hemolytic streptococcal pharyngeal infection. Effect of oxacillin.

Twelve pharyngeal specimens containing both group A hemolytic streptococci and coagulase-positive staphylococci were tested individually and together against penicillin-G and oxacillin. The hemolytic streptococci were always completely inhibited at very low concentrations of penicillin-G when tested individually. When combined with cultures of coagulase positive. penicillin-G destroying staphylococci, the inhibitory concentrations rose by a factor of 200. Similar tests with oxacillin showed no increase for inhibitory or bactericidal concentrations when the organisms were tested singly or in combination. Penicillin-G resistent staphylococci seemed to protect group A hemolytic streptococci from the action of penicillin-G. This was not the case when oxacillin was exhibited.