Antimicrobial resistant bacteria in aquatic systems represents one the greatest challenges and emerging threats since wateris one of the most relevant vehicles of bacterial dissemination. Monitoring the presence of antimicrobial resistance human pathogens, in particular staphylococci, may lead to a better understanding of the epidemiology of infections caused by these bacteria. Thus, we aimed to investigate the prevalence of Staphylococcus spp. in surface waters in Portugal.

Seventy-seven water samples (30 rivers, 18 streams, 11 irrigation systems, 10 dams, 5 fountains and 3 lakes) were collected from the hydrographic basins of Douro river in Trás-os-Montes and Alto Douro region, Portugal. Samples were filtered through a cellulose nitrate pore membrane filter. The filters were incubated at 37°C for 24 h in BHI broth supplemented with 6.5% of NaCl. After that, the inoculum was seeded on Mannitol Salt agar plates and incubated at 37°C for 24 h. Staphylococci species were identified by MALDI-TOF MS. Antimicrobial susceptibility testing was performed by the Kirby-Bauer disk diffusion method.

Seventy-five staphylococci were isolated from water samples of which 30 were coagulase-positive (CoPS) and 45 were coagulase-negative staphylococci (CoNS). Among the CoPS, 29 were identified as S. aureus and one as S. pseudintermedius. The CoNS isolated included S. sciuri, S. lentus, S. xylosus and S. epidermidis, among others. S. aureuswere susceptible to almost all antibiotics tested, and CoNS were mostly resistant to penicillin, clindamycin and fusidic acid.

This study demonstrated that staphylococci, including S. aureus, is present in surface waters. A high diversity of staphylococci was detected in surface water samples, in particular for CoNS.