Genotype and phenotype relationship in MLSB resistance in Streptococcus pyogenes and Streptococcus agalactiae isolated in central Italy

The aim of this work is to study a correlation between phenotype and genotype in clinical isolates of erythromycin-resistant Streptococcus spp. Among the 25 erythromycin-resistant S. pyogenes, we detected six strains with iMLS(B), nine with cMLS(B) and two with M phenotypes. Among 14 erythromycin-resistant S. agalactiae, we detected five strains with iMLS(B), seven with cMLSB and none with an M phenotype. Moreover, 8 S. pyogenes and 2 S. agalactiae showed a phenotype not matching the known ones described in literature, defining an "unknown phenotype". Upon examination, the genetic profiles, erm(A), erm(B) and mef(A), of the clinical isolates did not easily correlate with a specific phenotype. Our findings highlighted that the whole matter of phenotypic diversity in macrolide-resistant S. pyogenes and S. agalactiae strains and the correlation with their genetic profiles should be submitted to a more careful analysis of phenotypic and genotypic characterization.