Abstract
Summary
1. Twenty-three strains of beta hemolytic streptococci of groups A, B, and C were sub cultured serially on media containing streptomycin in an effort to induce resistance. The minimum increase in resistance after 40 transfers was 40-fold and the maximum 3000-fold. Most organisms, however, of all 3 groups showed increases of 100- to 400-fold.
2. The streptomycin sensitivity range for recently isolated strains of beta hemolytic streptococci is 10 to 50 μg/ml for 275 strains of group A, 30 to 400 μg/ml for 20 strains of group B, and 10 to 50 μg/ml for 47 strains of group C organisms.
3. Organisms which had acquired streptomycin resistance maintained it throughout subcultivations on blood agar medium.
4. Partial loss of resistance was observed in 5 of 6 strains on serial passages through mice.
5. Mouse virulence was decreased in 8 of 9 resistant organisms studied. Virulence was partially restored by passage through mice.
6. Group specificity was maintained by all resistant organisms.
7. Reduction in streptokinase production occurred in 2 of 23 resistant organisms and streptolysin S in 5 of 5 group A and C strains.
8. Transient changes in the colonial appearance and changes in hemolysis from beta to alpha or gamma types of colonies were demonstrated by all strains when growing on maximal concentrations of streptomycin. These colonies reverted to their original type when subcultured onto blood agar.
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