Staphylococcus pyogenes: the antibiotic sensitivity of strains isolated from human carriers

Abstract

Strains of Staphylococcus pyogenes able to grow in 0·1 unit/ml. of penicillin produced penicillinase and were regarded as resistant. The majority of the remaining strains had the same sensitivity as the standard sensitive staphylococcus.Five hundred and three strains were isolated from pre-clinical medical students from 1950 to 1953, and 24% were penicillin-resistant. Two per cent were streptomycin-resistant and none were resistant to chloromycetin, aureomycin or terra-mycin. Two hundred and forty-six of the strains were isolated from persistent and intermittent carriers, but only 14% were penicillin-resistant.Another 183 strains were isolated from persons unattached to hospital, and 14% were resistant to penicillin. Only one strain was streptomycin-resistant; one was chloromycetin-resistant and none were resistant to the other antibiotics.Among persistent and intermittent carriers, more than 7 times as many penicillin-resistant strains were isolated from those who had had previous penicillin therapy as from those who had not.It was concluded that the administration of antibiotic increases the number of resistant strains in the community.