Enterococcus Species and Their Antimicrobial Resistance in an Urban Watershed Affected by Different Anthropogenic Sources

Abstract

Different anthropogenic sources can have a significant influence on bacterial populations and their antimicrobial activities. In this study, the impact of anthropogenic activities on Enterococcus species was studied in an urban watershed in southern California affected by concentrated animal feeding operations (CAFOs), recreational activities, wastewater treatment plants (WWTPs), urban runoff, and control sites. Water samples were collected quarterly for two years for the enumeration of Enterococcus species based on the Enterolert most probable-number (MPN) assay. Concentrations of enterococci were higher in the sediment compared to surface water (4.5 × 106 CFU/g of sediment vs. 2.3 × 105 MPN/100 mL of water). The species diversity was dominated by E. mundtii (32%), E. faecalis (27%), and E. faecium (25%). E. faecium exhibited the highest antibiotic-resistant phenotype. Resistances were mostly to ciprofloxacin, erythromycin, and tetracycline. Tetracycline and erythromycin resistance genes, encoded by tet (C, K, O, S) and ermB, respectively, were more common in isolates from sediment (42.9%) compared to water (12.7%). E. mundtii was sensitive to ampicillin, chloramphenicol, gentamicin, and high levels of vancomycin. A significant percentage of E. faecalis were also resistant to these antibiotics. E. faecium and E. faecalis exhibited resistance to multiple antibiotics. Our data suggest that resistant Enterococcus species within the watershed might provide some useful data to determine pollutant types and sources in that watershed. Therefore, the widespread occurrence and abundance of E. faecium and E. faecalis, and their resistance genes associated with multiple antibiotics may potentially pose risks to the local populations exposed to these water sources during recreational activities.