Occurrence, species composition, and genetic diversity of enterococci in a Lake Superior Watershed.

Abstract

Fecal contamination of recreational waters is a widespread problem in the United States, resulting in beach closures, huge economic losses, and increased public health risk. In 2012, the U.S. EPA suggested coastal and Great Lakes states adopt enterococci as an alternative indicator for monitoring recreational water quality. However, little information is known about the occurrence and persistence of enterococci in freshwater environments. The overall objectives of the study were to examine the density, species distribution, and potential persistence of enterococci at two study sites in a Lake Superior watershed from May to September over a 2-year period. We also examined the genetic diversity of E. faecalis isolated in sands, sediments, water, and soils. Results of this study showed that enterococci were detected in 149 out of 159 samples (94%) by the MPN analyses and that their densities ranged from 3 to 5.6 x 105 MPN / 100 g sample. The densities were generally higher in the summers than those in other months examined. A total of 2,441 enterococcal isolates over the 2-year period were subjected to speciation. The composition of Enterococcus species was spatially and temporally dynamic, with the dominant species being: E. hirae, E. faecalis, E. faecium, E. mundtii, and E. casseliflavus, suggesting that enterococci in the study might have originated from environmental and fecal sources. Moreover, the genetic diversity of 536 E. faecalis isolates was assessed by HFERP DNA fingerprinting. Results indicated that the E. faecalis population in the watershed was genetically diverse, in part due to spatial and temporal changes. The recurrence of some E. faecalis fingerprints over multiple sampling events in soils and the occurrence of enterococci in the exclosure boxes suggested that some enterococci were persistent in soils for a prolonged time. However, enterococci did not appear to become naturalized in these environments. Our results also suggested that enterococci were transported between matrices within each site. My studies indicate that further research on the persistence of enterococci in soils and sands needs to be done before enterococci are used as a fecal indicator in freshwater ecosystems.