Differences in Survival among Enterococcus Faecalis Subspecies in Two Freshwater Creek Sediments

For bacterial source tracking (BST), the percentage of Enterococcus faecalis isolates among all fecal enterococci in an environmental water sample may serve as an inexpensive indicator of human and bird fecal contamination. Research suggests that some subspecies of fecal indicator bacteria are better adapted than others to survive environmental conditions. We determined the survival of seven different Ent. faecalis subspecies, three from different wastewater treatment plants and one from a latrine (presumably all of human origin), two from birds, and the American Type Culture Collection (ATCC) type strain, in two freshwater creek sediments, Saugahatchee Creek in Alabama and Tanyard Creek in Georgia. Ribotyping was used to identify different subspecies. Survival was determined in modified sentinel chambers (MicrofilterfugeTM tubes sealed at both ends with ≤0.45 μm membranes). Each Enterococcus ribotype was inoculated into sentinel chambers at approximately 10 bacteria per g dry weight of sediment, and the MostProbable Number (MPN) was estimated at Days 0 and 11. The MPNs of the seven Ent. faecalis subspecies declined 62.4 to 95.2 % in Alabama sediment; MPNs of the same subspecies declined 95.4 to 99.6% in Georgia sediment. There was no positive correlation among the subspecies that survived better in Alabama sediment and those that survived better in Georgia sediment. Statistical analyses suggest that not only did differences in survival exist among subspecies of Ent. faecalis, but also that differences existed between locations. However, in terms of BST, the rapid decreases in MPNs suggested that any subspecies adaptation to environmental conditions was minor.