Resistance to erythromycin and rising penicillin MIC in Streptococcus pyogenes in India.

There has been worldwide resurgence in the incidence of Streptococcus pyogenes infection and its sequelae. S. pyogenes remains uniformly susceptible to penicillin, and it is speculated that its minimum inhibitory concentration (MIC) has not changed during the past 70 years. The purpose of the present study was to determine the occurrence and pattern of resistance to penicillin and erythromycin amongst clinical isolates of S. pyogenes. A total of 34 clinical strains of S. pyogenes were identified by standard procedures. Antimicrobial susceptibility was analyzed by the Kirby-Bauer method of disk diffusion, and the E-test method was used to determine the MIC to penicillin and erythromycin. All the strains were sensitive to penicillin, clindamycin and vancomycin on disk diffusion. Ten (29.4%) strains were resistant to erythromycin. The pattern of macrolide resistance observed was M type. By the E-test method, 7 (20.6%) strains were penicillin nonsusceptible and 6 (17.6%) were erythromycin resistant. We concluded that surveillance of its susceptibility pattern is crucial to monitoring the development of antibiotic resistance in S. pyogenes.