Distribution of mef(A)-containing genetic elements in erythromycin-resistant isolates of Streptococcus pyogenes from Italy.

In total, 124 Streptococcus pyogenes isolates were obtained from throat cultures of different symptomatic patients. All isolates showed M-phenotype macrolide resistance and contained the macrolide efflux gene mef(A). The isolates were screened for the presence and insertion site of mef(A)-containing genetic elements. In 25.8% of the isolates, mef(A) was found to be carried by elements belonging to the Tn1207.3/Phi10394.4 family inserted in the comEC gene, while 74.2% contained chimeric elements with a different genetic structure and chromosomal location, probably associated with the recently described 60-kb tet(O)-mef(A) element.