Potential ofEnterococcus faecalisas a Human Fecal Indicator for Microbial Source Tracking

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Abstract
Regulatory agencies are interested in a fecal indicator bacterium with a host range limited to humans because human fecal contamination represents the greatest hazard to humans, yet is a relatively easy nonpoint source to remedy. Watersheds with human fecal contamination could be given first priority for cleanup. A fecal indicator bacterium with a host range limited to humans and a few other warm‐blooded animal species would also simplify microbial source tracking because only a few animal species would be required for any host origin database. The literature suggests that the fecal indicator bacteriumEnterococcus faecalishas a limited host range. On this basis, we selected this bacterium for study. Of 583 fecal streptococcal isolates obtained on Enterococcosel agar from Canada goose, cattle, deer, dog, human, chicken, and swine, 392 were considered presumptive enterococci and were subsequently speciated with the API 20 Strep system. Of these isolates, 22 wereEnt. durans(5.6%), 61 wereEnt. faecalis(15.6%), 98 wereEnt. faecium(25.0%), 86 wereEnt. gallinarum(21.9%), and 125 were unidentified (31.9%). The host range of theEnt. faecalisisolates was limited to dogs, humans, and chickens. Media were developed to isolate and identifyEnt. faecalisquickly from fecal samples and this scheme eliminatedEnt. faecalisisolates from dogs. When the remainingEnt. faecalisisolates were ribotyped, it was possible to differentiate clearly among the isolates from human and chicken. It may be that combining the potentially limited host range ofEnt. faecaliswith ribotyping is useful for prioritizing watersheds with fecal contamination.

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