Smal Typeability and Tetracycline Susceptibility and Resistance in Streptococcus pyogenes Isolates with Efflux-Mediated Erythromycin Resistance

摘要

In Streptococcus pyogenes, efflux-mediated macrolide resistance is encoded by the mef(A) gene and is associated with a particular resistance pattern (M phenotype) characterized by resistance, usually at a low level, only to 14- and 15-membered macrolides (10). The mef(A) gene is carried by different genetic elements, depending on whether the isolates are susceptible or resistant to tetracycline (2). In the tetracycline-suscep-tible isolates, mef(A) is contained in a Tnl207.1 transposon, identical to the one originally described hi S. pneumoniae (9), inserted into larger genetic elements of phage origin such as Tnl207.3 (8) or 10394.4, a related 58.8-kb chimeric element (1). In the tetracycline-resistant isolates, me/(A) is linked to the tet(O) gene hi a tet(O)-mef(A) chimeric element which, unlike the Tn1207.3-10394.4 family, may contain different, defective variants of the Tnl207.1 transposon and is not integrated into the chromosome within the comEC gene (2).