A Novel Erythromycin Resistance Methylase Gene (ermTR) in Streptococcus pyogenes

Erythromycin resistance among streptococci is commonly due to target site modification by an rRNA-meth-ylating enzyme, which results in coresistance to macrolide, lincosamide, and streptogramin B antibiotics (MLSB resistance). Genes belonging to the ermAM (ermB) gene class are the only erythromycin resistance methylase (erm) genes in Streptococcus pyogenes with MLSB resistance that have been sequenced so far. We iden-tified a novel erm gene, designated ermTR, from an erythromycin-resistant clinical strain of S. pyogenes (strain A200) with an inducible type of MLSB resistance. The nucleotide sequence of ermTR is 82.5 % identical to ermA, pre-viously found, for example, in Staphylococcus aureus and coagulase-negative staphylococci. Our finding provides the first sequence of an erm gene other than ermAM that mediates MLSB resistance in S. pyogenes. Three principal mechanisms have so far been found to be responsible for the acquired erythromycin resistance in bacte-ria: target site modification, enzymatic inactivation of erythro-mycin, and active efflux of erythromycin (20, 21). In strepto-cocci as well as in many other gram-positive bacteria, target site modification is a common resistance mechanism (45). It is due to the presence of an rRNA methylase that mono- o