Contamination level and location of recreational freshwater influence the ability to predict Escherichia coli concentration by qPCR targeting Bacteroides

Fecal bacteria are common microbial contaminants in freshwater with the potential to cause human illness. Detection of these microbes have traditionally relied on microbial plating to enumerate colonies of fecal indicator bacteria (FIB) such as Escherichia coli (E. coli), which can take 24 h or longer to complete. Quantitative PCR (qPCR) is a rapid and sensitive method for detection of FIB in recreational water that could compliment or potentially substitute for microbial plating. In this study, we have isolated DNA from the beach water on the shoreline at three different locations of Lake Erie and subjected these samples to qPCR to examine the relative abundance of Bacteroides. These values were compared to colony forming units (CFU) of E. coli. The resultant linear regressions between these different measurements of microbe concentration were used to determine the efficacy of qPCR targeting Bacteroides at predicting E. coli concentrations that are relevant for decision making by recreational water managers. Our findings indicate that the ability of Bacteroides to serve as an early predictive tool for E. coli CFU concentration depends on sample location and level of bacterial contamination, but can be used in some cases to supplement recreational water quality measurement and consequential management. ► QPCR targeting Bacteroides can, in some cases, correlate with E. coli CFU. ► The correlation of Bacteroides E. coli concentrations depends on sample location. ► Water management based on Bacteroides depends on bacterial contamination level.