Effect of Sublethal Concentrations of Penicillin on the Virulence and Antigenic Composition of Group a Streptococci

Abstract

AIICHAEL, J. GABRIEL (House of the Good Samaritan, Children's Hospital M\edical Center, 13oston, Mass.), BENEDICT F. MIASSELL, AND ROBERT E. PERKINS. Effect of sublethal concentrations of penicillin on the virulence and antigenic composition of group A streptococci. J.Bacteriol. 85:1280-1287. 1963.---Virulent strains of group A streptococci were grown in sublethal concentrations of penicillin and tested for possible changes in colonial morphology, virulence, and antigenic composition. After overnight growth in broth containing penicillin, there was a marked reduction in precipitable group A and M protein content of the bacteria. Upon transfer to broth without antibiotic, the streptococci regained their ability to produce these substances. After multiple transfers in broth containing nonbactericidal levels of penicillini, variants developed which lacked group and type substances and which were also relatively resistant to penicillin. These variants were avirulent for mice and

Antimicrobial chemotherapy in the dog

“…These claims appeared to gain further support from observations that multiplication among micro-organisms did not recommence for periods of 1 -6 to 6 hours after their exposure to benzylpenicillin and ampicillin ceased (Eagle, 1948(Eagle, , 1949Wilson & Rolinson, 1979). Furthermore, Michael, Massell & Perkins (1963) showed that, after exposure in vitro to sublethal benzylpenicillin concentrations (0.005 unit/ml), a Group A streptococcus had reduced virulence and antigenic properties, and so was more susceptible to the antibacterial action of normal human blood.…”