Antimicrobial resistance of Streptococcus pyogenes clinical strains.

Objective. To determine the antibiotic susceptibility of recent isolates of Streptococcus pyogenes and to evaluate the prevalence of macrolide-resista nt phenotypes. Material and methods. In 1999, we conducted a cross-sectiona l study at Mexico Children's Hospital "Federico Gomez", to analyze one hund red strains of S. pyogenes isolated from 1992 to 1998, in children with unc omplicated pharyngotonsillitis. Strains were frozen at the bacteriology lab until they were analyzed. Strains were tested for susceptibility against s ome beta-lactams, macrolides and clindamycin. Double-disk testing was carri ed out to evaluate erythromycin-resistant phenotypes. Data are presented us ing central tendency measures. Results. All tested strains were not resista nt to beta-lactams and clindamycin; 16% of the strains were resistant to ma crolides and all of them belonged to phenotype M. Conclusions. Susceptibili ty testing is recommended to identify possible changes in antibiotic resist ance to streptococci.