Abstract
It has not yet been reported that beta hemolytic streptococci acquire resistance to aureomycin in vitro. Paine, Collins, and Finland( 1 ) reported that one strain of Streptococcus mitis and one strain oif Str. pyogenes acquired no increase in resistance to aureomycin even after 60 subcultivations on antibiotic-containing medium, Harvey, Mirick, and Schaub( 2 ) demonstrated an 8-fold increase in resistance to aureomycin by a microaerophilic streptococcus and a 16-fold increase in resistance by a Str. faecalis. These organisms were isolated from 2 patients during a relapse after several weeks of treatment with aureomycin for subacute bacterial endocarditis. The resistant Str. faecalis grew more slowly and formed smaller colonies on blood agar. The resistance of this strain was not permanent since streptococci of the original sensitivity reappeared after several transfers on blood agar.
The present study was undertaken to compare the in vitro and in vivo development of aureomycin resistance by group A, B, and C beta hemolytic streptococci, and to determine whether or not aureomycin altered the biology of the streptococcus in a manner similar to that produced by penicillin, ( 3 4 5 6 ) streptomycin,( 7 ) and bacitracin.( 8 , 9 )
Materials and methods. Resistance to aureomycin was induced in 23 strains of beta hemolytic streptococci: 8 of group A, 8 of group C, and 7 of group B. Parent strains and their designations are the same as those used in preceding studies. ( 3 4 5 6 7 ) Aureomycin sensitivity was determined by the whole plate method and was taken as the maximum concentration of antibiotic that permitted'good growth. Bacto heart infusion agar (Difco) containing 5% defibrinated sheep's blood and varying concentrations of aureomycin HOI (Lederle A377, Lot No. 7-8411) were used in 100 mm Petri dishes. Fresh dilutions of the yellow crystalline salt were prepared daily in physiological saline at a pH of 3.1.
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