Distribution and Diversity of Enterococcus Species in An Urban Watershed.

Enterococci are indicator bacteria used to assess the risk of acquiring enteric disease from swimming in marine waters. To address the environment as a potential source of Enterococcus species, we investigated levels of species diversity and the geographic and temporal variation of different species from surface waters in a region of southern California (United States) with a history of high concentration of cattle in a mixed urban setting.  Quarterly water samples were collected from seventeen stations in the middle Santa Ana River Watershed for two years. Enterococcus Species were enumerated using the most probable-number (MPN) assay. Higher concentrations of enterococci (up to 4.5 x 10⁶ CFU/g of sediment) or (up to 2.3 x 10⁵ MPN/100 ml of water) were observed in the creeks and channels compared to less than 1.6 x 10² in the control sites and effluent from waste water treatment plants.  T he most prevalent were Enterococcus faecium (32 % of isolates), Enterococcus faecalis (31%), Enterococcus mundii (26%), and others (11%). Isolates were resistant mainly to tetracycline (28%), erythromycin (22%), kanamycin (13.0%), and ampicillin (9%). The most common tet gene was tet(B). The results of this study suggest that Enterococcus species abundance and diversity in the environment vary temporally and is strongly influenced by seasonal precipitation and water temperature.