Persistence and growth of the fecal indicator bacteria, enterococci, in natural estuarine plankton communities

Enterococci are used as an indicator of fecal pollution to evaluate water quality in marine environments. The presence of enterococci as a group is not only associated with humans, but also has been found in the digestive tracts of other warm-blooded animals, in soil, on plant material and associated with plankton. Given the epiphytic nature of many Enterococcus spp., we investigated the contribution of plankton-associated enterococci in estuarine water samples. Our results suggest that Enterococcus spp. may be highly concentrated in plankton. Laboratory microcosm experiments showed the ability of E. faecalis, a fecal species and E. casseliflavus, an epiphytic species, to survive and grow in mixed plankton at 30 and 10oC. Therefore, aquatic biota such as plankton can serve as a reservoir for Enterococcus species. Moreover, our findings could have implications for the effectiveness of enterococci as an indicator of coastal water quality.