Tracking the Culprits: Microbial Source Tracking Uncovers Elevated Fecal Indicators along the Texas Coast

Aims: To utilize microbial source tracking to detect and differentiate sources of fecal bacteria in Texas, addressing the limitations of dated culture-based Enterolert tests, which quantify fecal indicator bacteria (FIB) but fail to indicate the source of the pollution. Study Design: This study involved quantification of FIB using some DNA-based tests validated by the United States Environmental Protection Agency (EPA). Place and Duration of Study: Water samples were collected from two counties along the Texas coast from February 2022 through June 2023. Methodology: EPA Method 1696 was conducted on 198 water samples collected for the detection of human-associated Bacteroidales by HF183/BacR287 quantitative polymerase chain reaction (qPCR) assay. A human-associated Enterococcus qPCR assay was also performed on a subset of Enterococcus isolates subcultured from Enterolert IDEXX trays to further test for the presence of human fecal contamination. A general Bacteroidales qPCR assay was also conducted to detect fecal contamination from various endothermic animals. These additional qPCR assays were used to detect FIB from avian, equine, ruminant, bovine, swine, and canine sources. Results: Although no samples tested positive for human-associated Bacteroidales, 7.6% of the subcultured samples tested positive for human-associated Enterococcus. All samples were positive for general Bacteroidales markers, and most samples were positive for avian FIB, while FIB from other animal sources were absent or detected in less than 5% of samples. Conclusion: This study provides insight into human and non-human contributions to high FIB counts in recreational waters along the Texas coast. Understanding these sources may improve water quality management and public health efforts.