Antimicrobial sensitivity and characterization of Streptococcus pyogenes strains isoleated from a scarlatina outbreak

OBJECTIVE: To evaluate the in vitro activities of 13 antimicrobial agents against 47 group A Streptococcus pyogenes (GAS) strains, and to determine the presence of genes encoding streptococcal pyrogenic exotoxin A (SpeA) and the M-protein serotypes. MATERIALS AND METHODS: A cross-sectional study was conducted at Centro de Salud Dr. Jose Castro Villagrana, during a scarlet fever outbreak occurring between December 1999 and January 2000, among 137 children at Colegio Espiritu de America. Minimum Inhibitory Concentrations (MICs) were obtained by the semiautomated microdilution method. Automated DNA sequencing was used for analysis of sequence variation in genes encoding the M protein, and SpeA. RESULTS: All strains were sensitive to betalactams and clindamycin. Six (12.7%) were resistant to erythromycin. The M2 type was the most frequently isolated GAS (27); almost all (96%) bacteria with the SpeA gene had the gene encoding the M2 protein. CONCLUSIONS: The recent resurgence of GAS infections calls for molecular epidemiology research and studies on the sensitivity to macrolides and beta-lactams.