Clonal differences among erythromycin-resistant Streptococcus pyogenes in Spain

The aim of this study was to determine whether the high levels of erythromy cin resistance in Streptococcus pyogenes found in Spain are due to the intr oduction and spread of one or more clones. Phenotypic and genotypic techniq ues were used to characterize all erythromycin-resistant S. pyogenes (ErR) isolated in Gipuzkoa, Spain, in the last 10 years and 128 ErR isolated in V itoria and Madrid during 1996. Of 437 ErR, 97% had the M phenotype; all 283 of the strains studied had the mefA determinant of resistance. After bioty ping, T serotyping, emm typing, and genotyping, four major clones were dete cted. Clones B (biotype I, type T4, emm4, pulsed-field gel electrophoresis [PFG E] II) and D (biotype V, type T8.25, emm75, PFGE IV) comprised 78.8% o f all ErR. The resistance of S. pyogenes to erythromycin was mainly due to an efflux mechanism of resistance (M phenotype); few crones were responsibl e for it.