Microbial Source Tracking in Two Nova Scotia Watersheds

Abstract

Halifax Water (HW) manages two source water systems, Lake Fletcher and the Musquodoboit River, where elevated levels (>200 CFU/100 mL) of Escherichia coli are common. Host-associated Bacteroidales order 16S rRNA gene-based microbial source tracking markers and human and cow mitochondrial DNA (mtDNA) markers were used to determine sources of fecal contamination in both watersheds. Human Bacteroidales markers were found at all sites except for the upper woodland site in the Lake Fletcher watershed. Higher rates of Listeria monocytogenes, Campylobacter jejuni and E. coli O157:H7 were detected in the Middle Musquodoboit (MM) watershed. Serogrouping of presumptive L. monocytogenes isolates showed the IIa (1/2a, 3a serovars) and IIb (1/2b, 3b serovars) serogroups were prevalent in both watersheds. Detection of E. coli weakly predicted Campylobacter and Salmonella occurrence in both watersheds (OR >1, p-value <0.001). Results suggest failing onsite wastewater systems are the leading cause of fecal pollution in both watersheds.