STUDIES ON ANTIBIOTIC SYNERGISM AND ANTAGONISM

Abstract

Penicillin, streptomycin, bacitracin, neomycin, aureomycin, chloramphenicol, and terramycin were tested alone and in pairs against Streptococcus faecalis, S. pyogenes, Staphylococcus aureus, Klebsiella pneumoniae, and Proteus vulgaris. Broth containing antibiotics was inoculated with 107-108/ml. bacteria at 37[degree]C and the no. of viable organisms detd. at intervals by plate counts. Synergism, an increase in bactericidal rate within 24 hrs. as compared to the rate with either drug alone and killing of greater nos. of bacteria than from simple summation, was shown by various pairs of drugs. Antagonism, a decrease in bactericidal rate as compared to the more active drug, was shown by certain pairs. A given pair might show synergism toward one sp., or even a strain, of bacteria, and antagonism toward another. At least 1 of a synergistic pair must be at least bacteriostatic alone. Synergism is reciprocal; either drug in active concn. may be combined with a less effective or often ineffective concn. of the other. Given pairs in varying concn. did not show both synergism and antagonism against a given organism. A hypothetical scheme of combined action is present.