Tracking the sources of fecal contamination in the Wissahickon Creek Watershed using phenotypic and genotypic analytical methods

Microbial source tracking is a relatively new research approach to identify sources of human and animal fecal pollution based on the assumption that intestinal bacteria of warm-blooded animals and humans differ because of gut conditions and natural selection. Advancements in both genotypic and phenotypic methods have contributed to the development of targeted approaches in water pollution prevention, control and remediation. The aim of these techniques is to assist the implementation of a targeted approach for watershed management practices.;The focus of this research is the Wissahickon Creek sub-watershed. Over a 22-month period, surface water, wastewater treatment plant effluent and fecal samples were collected for the isolation of Escherichia coli and Enterococcus spp. The isolates were biochemically confirmed, and subjected to antibiotic resistance analysis and a polymerase chain reaction-based method to characterize their phenotypic and genotypic traits. The libraries of data were analyzed using statistical tests to determine how well individual isolates represented source groups, and classification methods to determine the rates of correct classification of individual and combined source groups. Based on these investigations, it was shown that antibiotic resistance analysis needed further procedural development to be an adequate instrument for the source assignment of isolates from surface water samples. The polymerase chain reaction-based method was better suited to the objective of source assignment, as the rates of correct classification were superior.;Data analysis methods were chosen to incorporate techniques that have been used in source tracking studies, in addition to those that have been recommended for use but have not been tested in practice. Discriminant analysis was applied to the datasets, as it has been the classification method of choice for many researchers. However it was shown that the k-nearest neighbor analysis generated higher rates of correct classification for the known source isolates and thus was used for the source assignment of isolates from water samples. Examination of the genotypic data suggested that the dominant source of bacterial contamination in the creek was wastewater treatment plant effluent. For the phenotypic data, the dominant source was determined to be livestock, but the sufficiency of the phenotypic data was questionable.;Keywords. Microbial Source Tracking; Genotypic methods; Phenotypic methods; E. coli; Enterococcus spp.