emm Gene Distribution among Erythromycin-Resistant and -Susceptible Italian Isolates of Streptococcus pyogenes

Abstract

ABSTRACT The phenotypes and genetic determinants for macrolide resistance were determined for 167 erythromycin-resistant Streptococcus pyogenes strains. A cMLS phenotype was shown in 18% of the erythromycin-resistant strains, while inducible resistance was apparent in 31% and the M phenotype was apparent in 50%. The emm gene type of this set of resistant isolates and that of 48 erythromycin-sensitive isolates were determined. emm 2 and emm 48 were recorded only in the resistant strains of the M phenotype, while approximately all of the strains harboring the emm 22 gene had the cMLS phenotype. More than 80% of the emm 89-positive strains had the iMLS phenotype, and the same portion of emm 4 strains presented the M phenotype. emm 3 is recorded only among sensitive strains. The distribution of frequencies of the genetic determinant for the virulence factor M protein was significantly different both among organisms of different types of resistance and between resistant and sensitive populations of S . pyogenes under study.