Bacterial Indicators of Fecal Pollution: Exploring Relationships between Fecal Coliform and Enterococcus Groups in Central and South Florida Surface Waters

Ambient and recreational surface waters worldwide experience fecal pollution due to a variety of anthropogenic sources. Fecal waste has been proven, for over a century, to harbor pathogenic microorganisms which subsequently cause a variety of disease and illness in human hosts. The benefits of utilizing fecal indicator bacteria (FIB) as a simple, inexpensive means to detect fitful human pathogens within a variety of water matrices are vast. However, no universal agreement exists in regard to which indicator is best suited for detection of fecal contamination and pathogens in environmental waters, and no single standard for bacterial indicators has been federally mandated. This study sought to explore the potential benefits of a multiple-indicator approach to water quality analysis of fresh and brackish surface waters. The distribution and fluctuation of two frequently used, EPA approved groups of FIB – fecal coliform and Enterococcus – were explored, and relationships between the two FIB groups were examined in fresh and brackish surface waters of Central and South Florida. Samples were collected over a period of 12 consecutive months, spanning April 2015 through March 2016, and analyzed using membrane filtration procedures outlined in Standard Methods 9222D and EPA method 1600. Raw and log transformed colony forming unit (CFU) data, per 100 mL, was analyzed annually and seasonally through linear regression, Spearman correlation, and exploratory data analysis techniques performed in R-Studio. The results of this study showed a moderate to strong relationship between fecal coliform and Enterococcus under both fresh and brackish conditions. The presence of a positive, linear relationship between fecal coliform and Enterococcus in both fresh and brackish water was apparent in both seasonal and annual regression analysis; upward and downward fluctuation(s) in one variable was shown to predict similar fluctuation(s) in the other year-round. However, while fecal coliform and Enterococcus showed moderate to strong correlations, causation was not implied. Low R2 values showed that the FIB groups were not dependent upon one another in any case, either annually or seasonally. The results of this study challenge previously accepted views of fecal coliform and Enterococcus effectiveness as ideal fresh and brackish water FIB, their suitability as sole indicators of fecal pollution, and their ideal usage as indicators for waters of varying salinities; results support those previously seen in studies such as Hanes and Fragala 1967, which emphasize the need for a multiple indicator approach to water quality analysis of ambient and recreational waters experiencing brackish conditions