Evaluation of Enterococcus concentrations at beaches in Door County, WI (Lake Michigan, USA) by qPCR and defined substrate culture analysis

The US EPA (Environmental Protection Agency) has approved the use of a quantitative polymerase chain reaction (qPCR) method for surface water regulatory decisions. This method would allow for results in as little as 4 h, rather than the 24 + hours for culture-based tests. The US EPA qPCR Method 1611 is enterococci-based, whereas the Great Lakes states adopted Escherichia coli as the indicator organism of choice. The change in indicator organism, method, and the heterogeneous nature of Great Lake beaches present challenges to implementation of rapid methods. The objective of this study was to determine the feasibility of using qPCR for beach water monitoring and management in rural, northern Lake Michigan communities. Concentrations of fecal indicator bacteria (FIB) were different in each method and varied greatly by beach. When concentrations of enterococci by TaqMan Enterococcus qPCR (EntTaq) were compared with E. coli using Colilert, positive correlations were detected only at Baileys Harbor, Fish Creek and Sunset Park Beaches (r2 = 0.26, r2 = 0.22 and r2 = 0.36, respectively). When enterococci concentrations determined by EntTaq were used for management decisions, the EntTaq method would have resulted in 47 false positive and 27 false negative results when compared to culture-based decisions. When management decisions based on E. coli concentrations were obtained from Colilert, EntTaq would have resulted in 35 false positive and 49 false negative results. This study suggests that, although minimally trained individuals can obtain appropriate results using qPCR methods, each beach community should carefully evaluate the impact of adopting rapid methods for beach management decisions.