School of Life Sciences' Friday Seminar

December 12, 3:30pm - 4:30pm
Mānoa Campus, Bilger 152

MS Thesis Defense: "Integrated Assessment of Fecal Indicator Bacteria (FIB) and Microbial Source Tracking (MST) in American Samoa Watersheds" - Speaker: Nu Jabin, Microbiology MS student, ÃÛÌÇÖ±²¥ ²ÑÄå²Ô´Ç²¹ * Abstract: American Samoa (AS) watersheds support various ecosystem services. The rapidly growing island population and its needs can compromise the water quality in the watersheds, posing a risk to public health and ecosystem integrity. Currently, AS relies on standard fecal indicator bacteria (FIB), namely enterococci and Escherichia coli, for monitoring stream and beach water quality, much like the US. This study assessed 50 soil and 41 water samples across five watersheds (classified from pristine to extensive) for FIB (enterococci, E. coli, Clostridium perfringens) and MST markers (human-associated CrAssphage and HF183, dog-associated BacCan-UCD, and pig-associated Pig-2-Bac). STV-based water quality standards for enterococci (130 MPN/100ml) and E. coli (410 MPN/100ml), utilized in AS, were not met by 80.5 and 65.9% of the stream samples, respectively. At least one of the four MST markers was detected in 36.4% and 44.4% of the water samples that did not comply with the enterococci or E. coli standards, respectively. At least one of the two human-associated markers were detected in 27.3% and 33.3% of the water samples that did not comply with the enterococci or E. coli standard, respectively, therefore indicating that the source of elevated levels of indicator bacteria in the majority of the cases was not sewage. Concentrations of the markers in the samples positive for markers did not correlate with any of the FIB tested (P>0.05 on all tests). Detection of human-associated markers was limited to two out of the five watersheds classified as extensive. Our limited validation of MST markers based on the 37 fecal samples of animals common in AS (farm pigs, dogs, fruit bats, chickens, birds) and six wastewater samples collected from two treatment plants indicated 100% sensitivity for all four markers. Human-associated marker (HF183) was detected in a single dog fecal sample (97.3% specificity), and dog-associated markers (BacCan-UCD) were detected in two chicken and pig samples (89.2% specificity); no cross-reactivity of CrAssphage and Pig-2-Bac were detected. All soil samples were negative for the human-associated markers, but dog-associated and pig-associated markers were detected in two and one soil sample, respectively. Both enterococci and E. coli were detected in 92.0% of soil samples, averaging 954 MPN/g and 1,375 MPN/g, respectively, likely implicating soils as the major source of elevated levels of FIB in AS watersheds.


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