Use of composite data sets for source-tracking enterococci in the water column and shoreline interstitial waters on Pensacola Beach, Florida

Sources of Enterococcus faecalis isolates from Pensacola Beach, FL. were identified using a library-based approach by applying the statistical method of average similarity to single and composite data sets generated from separate analyses. Data sets included antibiotic resistance analysis (ARA), rep-fingerprints, and fatty acid methyl ester (FAME) profiles. Use of a composite data set composed of ARA and rep-fingerprints, added to the confidence of the identifications. The addition of FAME data to composite data sets did not add to the confidence of identifications. Source identification was performed to better understand risk associated with higher densities of enterococci found in swash zone interstitial water (SZIW) as compared to adjacent bathing water on Pensacola Beach, FL. The “swash zone” is that area of the beach continually washed over by waves. As the potential sources of enterococci were limited in this environment, only two library units, sea gull and human, were constructed. Identification of the beach isolates using a composite data set indicated a sea gull origin. The clonality of the beach isolates suggested that the beach environment selects certain subspecies of E. faecalis.