Penicillin tolerance among 67 strains of beta-hemolytic
streptococci was examined by determining the ratio of the
minimal bactericidal concentration to the minimal inhibitory
concentration as 32 or greater. Tolerance was demonstrated in
15 group A strains and in 11,7, and 4 of groups B, C and G,
respectively. Thereafter the effects of a subminimal
inhibitory concentration (1/2 MIC) of penicillin on the
bacterial products of four tolerant and four nontolerant
strains (two of each Lancefield group) were analyzed and
compared. The antibiotic caused a marked increase in the
expression of the group carbohydrates for strains of group B.
Penicillin was found to reduce the cell-bound hemolysin
activities of the four tolerant strains and to increase the
activity of the other (free) form of nontolerant groups A, C
and G hemolysins. Penicillin caused an increase in the
extracellular hyaluronidase activities of one group A and
groups B, C and G streptococci. With added antibiotic the
production of deoxyribonuclease by tolerant groups A, C and G
was greatly enhanced and that of the group B streptococcus
was arrested.
