Molecular typing of erythromycin-resistant Streptococcus pyogenes strains with the M phenotype isolated in Italy

To assess the spread of the new M phenotype, various erythromycin-resistant Streptococcus pyogenes strains from three Italian cities (Verona, Monza, F lorence) were characterised. Each strain was analysed for the presence of g enes ermAM and mefA, for the ability to accumulate radioactive erythromycin in the absence of sodium arsenate, for the protein T serological type, and for the DNA macrorestriction profile identified by means of pulsed-field g el electrophoresis. In a number of strains, the presence of the inducible e rmAM gene was demonstrated; all these strains were negative in the efflux-p ump detection assay, did not possess the mefA gene, and had similar restric tion profiles. The strains with the efflux mechanism and mefA gene belonged to different serotypes. Of these, only one serotype, T4, was isolated in a ll three cities. The restriction profile analysis with SmaI and SfiI reveal ed a very close correlation between strains with the same serotype.