Background: Enterococci, ubiquitous colonizers of humans and other animals, play an increasingly important role\r\nin health-care associated infections (HAIs). It is believed that the recent evolution of two clinically relevant species,\r\nEnterococcus faecalis and Enterococcus faecium occurred in a big part in a hospital environment, leading to\r\nformation of high-risk enterococcal clonal complexes (HiRECCs), which combine multidrug resistance with increased\r\npathogenicity and epidemicity. The aim of this study was to establish the species composition in wastewater, its\r\nmarine recipient as well as a river estuary and to investigate the antimicrobial susceptibility of collected isolates.\r\nMolecular methods were additionally applied to test the presence of HiRRECC-related E. faecium.\r\nResults: Two wastewater treatment plants (WWTPs), their marine outfalls and Vistula river that influence\r\nsignificantly the quality of waters in Gulf of Gdansk were sampled to investigate the presence of Enterococcus spp.\r\nFour-hundred-twenty-eight isolates were obtained, including E. faecium (244 isolates, 57.0%), E. hirae (113 isolates,\r\n26.4%) and E. faecalis (63 isolates, 14.7%); other species (E. gallinarum/casseliflavus, E. durans and E. avium) accounted\r\nfor 1.9%. Antimicrobial susceptibility testing revealed the presence of isolates resistant to erythromycin, tetracycline,\r\namipicillin, fluoroquinolones and aminoglycosides (high-level resistance), especially among E. faecium, where such\r\nisolates were usually characterized by multilocus sequence types associated with nosocomial lineages 17, 18 and\r\n78 of this species representing HiRECC, formerly called CC17. These isolates not only carried several resistance\r\ndeterminants but were also enriched in genes encoding pathogenicity factors (Esp, pili) and genes associated with\r\nmobile genetic elements (MGE), a feature also typical for nosocomial HiRECC.\r\nConclusions: Our data show that WWTPs constitute an important source of enterococcal strains carrying\r\nantimicrobial resistance determinants, often associated with the presence of MGE, for the recipient water\r\nenvironment, thus increasing a pool of such genes for other organisms. The presence of HiRECCs in wastewaters\r\nand marine/river environment may indicate that adaptations gained in hospitals may be also beneficial for survival\r\nof such clones in other settings. There is an obvious need to monitor the release and spread of such strains in\r\norder to elucidate better ways to curb their dissemination.
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