Comparative Genomic Analyses Reveal Potential Factors Responsible for the ST6 Oxacillin-Resistant Endemic in a Hospital.

Oxacillin-resistant (ORSL) is considered a life-threatening isolate in healthcare settings. Among ORSL clones, ST6-SCC II strains are associated with an endemic spread in hospitals. We analyzed the complete genome of ORSL CGMH-SL118, a representative strain. Results revealed that this strain contained three MGEs (two prophages and one plasmid) other than the SCC II element, which showed remarkable differences in genome organization compared to the reference strains from NCBI. Eight multidrug-resistant genes were identified. All but were carried by MGEs, such as the SCC II element [, (9)-Ia, and ] and the prophage φSPbeta [ (6')- (2'), (3')-III, and (6)-Ia], indicating that MGEs carrying multidrug-resistant genes may be important for ST6 strains. The prophage φSPbeta contains gene, which was responsible for the pathogenesis of . A phage-mediated resistant island containing (SlRI ) was found near φSPbeta, which was highly homologous to type III SeRI of . In contrast to previous studies, over 20% of ST6 isolates showed a fusidic acid-resistant phenotype, suggesting that phage-mediated intraspecies transmission of resistant islands may become an important issue for ST6 strains. Sixty-eight clinical isolates of ST6 (50 OSSL, oxacillin-sensitive , and 18 ORSL, including CGMH-SL118) collected from various types of specimens in the hospital were studied. Among these isolates in this study, ORSL showed similar drug-resistant genes and phenotypes as CGMH-SL118. The comparative genomic analyses highlight the contribution of MGEs in the development and dissemination of antimicrobial resistance in ST6 strains, suggesting that resistance determinants and virulence factors encoded by MGEs provide a survival advantage for successful colonization and spread in healthcare settings.