A cell viability assay was applied to measure bacterial enteric pathogens in a river in southern Ontario, Canada that is used as a source of drinking water. Pathogen concentrations were measured using both propidium monoazide (PMA)-quantitative polymerase chain reaction (PCR) and quantitative PCR (qPCR) without PMA pretreatment to compare viable and total (live and dead) cells. The pathogens evaluated were Salmonella enterica, thermophilic Campylobacter, and Escherichia coli O157:H7, and the suspected enteric pathogen Arcobacter butzleri was also investigated. Results showed that for all strains dead cells were detected in few river water samples, and the difference between total and viable cell concentrations for each pathogen group was always less than 0.5 log. A. butzleri was detected at concentrations 2–3 log higher than the other pathogens. S. enterica, Campylobacter, and E. coli O157:H7 were detected at low concentrations at one sample location and at higher concentrations at a second sampling location. Results from this study show qPCR with PMA pretreatment can provide reliable enumeration of viable pathogens in surface water, and that dead cells were rarely present in water used as a source for drinking water treatment.

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