부산대학교 도서관

ABSTRACTAs opposed to Enterococcus faecalis, which is intrinsically resistant to lincosamides, streptogramins A, and pleuromutilins (LSAP phenotype) by production of the ABC protein Lsa(A), Enterococcus faeciumis naturally susceptible. Since this phenotype may be selected for in vivoby quinupristin-dalfopristin (Q-D), the aim of this study was to investigate the molecular mechanism of acquired LSAP resistance in E. faecium. Six LSAP-resistant in vitromutants of E. faeciumHM1070 as well as three different pairs of clinical isolates (pre- and postexposure to Q-D) were studied. The full genome sequence of an in vitromutant (E. faeciumUCN90B) was determined by using 454 sequencing technology and was compared with that of the parental strain. Single-nucleotide replacement was carried out to confirm the role of this mutation. By comparative genomic analysis, a point mutation was found within a 1,503-bp gene coding for an ABC homologue showing 66% amino acid identity with Lsa(A). This mutation (C1349T) led to an amino acid substitution (Thr450Ile). An identical mutation was identified in all in vitroand in vivoresistant strains but was not present in susceptible strains. The wild-type allele was named eat(A) (for EnterococcusABC transporter), and its mutated allelic variant was named eat(A)v. The introduction of eat(A)vfrom UCN90B into HM1070 conferred the LSAP phenotype, whereas that of eat(A) from HM1070 into UCN90B restored susceptibility entirely. This is the first description of the molecular mechanism of acquired LSAP resistance in E. faecium. Characterization of the biochemical mechanism of resistance and the physiological role of this ABC protein need further investigations.