Abstract
Summary
The penicillin G- and nafcillin-mediated lysis of growing cells of S. aureus by lysozyme and trypsin was used as a test to determine the influence of sublethal concentrations of other antibiotics on this response. Seventeen antibiotics were tested with two strains of S. aureus (G50 and CHP). Rifamycin, novobiocin, tetracycline HCl, actinomycin D, erythromycin, and streptomycin interfered with or blocked lysis whereas methicillin, cephalothin, cloxacillin, dicloxacillin, cycloserine, and vancomycin either enhanced it or had no effect depending on the concentrations of these antibiotics. Rifamycin, chloramphenicol, and novobiocin were found to be the most active antagonists of penicillin G and nafcillin. Under the experimental conditions, none of the bactericidal antibiotics acted synergistically with either penicillin G or nafcillin. The results suggest that the change in lytic activity when certain antibiotics are combined with penicillin depends on some specific biologic activity against S. aureus by which these antibiotics directly or indirectly reduce the ability of the penicillin to block cell wall synthesis.
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