The genus Enterococcus stands out as one of the main causes of healthcare-associated infections (HAIs), with vancomycin-resistant Enterococcus faecium (VREfm) considered high-priority pathogens in terms of antimicrobial resistance (AMR) by the World Health Organization (WHO). They are sentinel microorganisms for the spread of AMR in the One Health context and can be found in marine environments. Considering these aspects, this study aimed to characterize the phenotypic and genotypic antimicrobial resistance of enterococci isolated from coastal waters of representative beaches of the Guanabara Bay (Icaraí and Jurujuba) and the oceanic region (Piratininga) of Niterói-RJ.

A total of 37 water samples collected between 2022 and 2023 were analyzed. The samples were identified by mass spectrometry (MALDI-TOF MS), followed by disk diffusion and Minimum Inhibitory Concentration (MIC) determination by E-test, to assess the phenotype of vancomycin resistance. For genotypic analysis, detection of vancomycin resistance genes (vanA, vanB, and vanC1) was performed, followed by Sanger sequencing.

Among the results obtained, five distinct species were identified, with E. faecium being prevalent (48.65%), followed by E. faecalis (24.32%), E. casseliflavus (10.81%), E. hirae (10.81%), and E. gallinarum (5.41%). Regarding isolation sites: Jurujuba Beach (22) > Icaraí (8) > Piratininga (7). Of the 20 samples subjected to disk diffusion testing, 17 were sensitive and 3 intermediate to vancomycin. All were susceptible to teicoplanin. Although the vanA gene was not found, the vanB gene was detected in 3 samples: VREfm (MIC: 4 μg/mL) and E. gallinarum (MIC: 3 μg/mL, vanC1) isolated from Icaraí, and VREfm (MIC: 0.38 μg/mL) isolated from Jurujuba, the latter with sequence confirmed and > 99% identity with the vanB gene of E. faecium.

Although the strains are not expressing vancomycin resistance in vitro, the presence of vanB in isolates from coastal waters is concerning, as this phenotype may be expressed in vivo, and vancomycin is one of the last-resort antimicrobials for treating infections caused by E. faecium. Therefore, continuous environmental surveillance of vancomycin resistance genes in these bacteria is essential, given their potential to pose a public health threat.