Abstract
Summary
1. Ten strains of Group B streptococci were transferred serially on media containing increasing quantities of penicillin in an effort to produce resistance. All 10 organisms showed a significant increase in resistance varying from 11 to 190-fold over the parent strains.
2. No increased resistance was induced by serial transfers on control medium.
3. In contrast to Group A organisms, Group B streptococci did not lose resistance on subculture on blood agar or on serial passage through mice.
4. Virulence decreased in all resistant strains of streptococci. The pathogenicity was partially restored in one organism but remained unchanged in two after passage in normal mice.
5. In only 2 resistant strains was the group specificity lost.
6. Transient alterations in the colonial appearance, and changes in hemolysis from beta to alpha or gamma were demonstrated by all strains when grown on maximal concentrations of penicillin. These colonies reverted to the parent type when subcultured on blood agar.
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