Tracking Sources of Fecal Pollution in a South Carolina Watershed by Ribotyping Escherichia coli: A Case Study

Abstract

Fecal pollution of water systems can exact high risks to human health and can result in significant economic losses due to closures of beaches and shellfish harvesting areas. The ability to effectively track the sources of pollution within a watershed is imperative for proper risk assessment and remedial efforts to be evaluated and enacted. Several microbiological, genotypic, phenotypic, and chemical methods have been proposed as useful tools for tracking the sources of fecal pollution. Here, we describe the effective use of the ribotyping microbial source tracking procedure to determine the source(s) of Escherichia coli within a South Carolina watershed. In this study, 92% of animal-derived E. coli isolates collected were correctly classified as being of animal origin using our existing ribotype profile database. These results suggest that the temporal and spatial diversity of E. coli may not be a significant factor in broad source (human versus animal) classification of E. coli by using our ribotyping DNA fingerprinting procedure. In addition, direct matching of ribotype profiles from water samples to those from known animal sources was used as an index of the potential predominant sources of fecal input(s) into this watershed. This method was useful in assessing possible specific animal sources when statistical analysis of a ribotype profile indicated general animal fecal pollution. Prior to investigating potential fecal inputs into this watershed, a significant human source was suspected as the primary input; however, of the 515 E. coli isolated from water samples collected during the course of this study, 88% were typed as being of animal fecal origin. Thus, this study was integral in the realization that animals may be a significant source of contamination and that remediation efforts should be redirected to accommodate these findings. This study summarizes one of the few case studies in which ribotyping was successfully utilized to further resolve a “true-life” water quality and management problem.