Induced Resistance of Staphylococcus aureus to Various Antibiotics

Abstract

S. aureus 209P (ATCC 6538P) can develop marked resistance to peni- cillin, streptomycin, and the active principle "A" of Asarum canadense, an intermediate degree of resistance to both pyocyanin and gliotoxin, but very little resistance to allyl-2-propene-1-thiolsulfinate, Hg Cl2, or to the active principle of Arctium minus. It did not develop resistance to aspergillic acid. S. aureus has been rendered resistant to a conc. of penicillin of 4 mg./ml. At a conc. of 1 mg./ml. the characteristic biochem. reactions of S. aureus were lost, and the organism became markedly pleomorphic and Gram-negative. The resistance of the strain was apparently stabilized by repeated transfers in broth containing 4 mg./ml. of penicillin. The biochemical, tinctorial, and morph. characteristics of the parent culture were regained when the strain that was resistant to 1 mg./ml. of penicillin was cultured in penicillin-free medium. During 12 transfers in increasing concns. of streptomycin, S. aureus developed a resistance to 4 mg./ml. of that antibiotic. All of the characteristic biochemical reactions of the organisms were suppressed at this level of resistance, but no noticeable change in morphology was observed. At high levels of resistance to penicillin and streptomycin, slight cross resistance to these antibiotics was demonstrated.