Quantitative real-time PCR analysis of total and propidium monoazide-resistant fecal indicator bacteria in wastewater

Abstract

A real-time quantitative PCR (qPCR) method and a modification of this method incorporating pretreatment of samples with propidium monoazide (PMA) were evaluated for respective analyses of total and presumptively viable Enterococcus and Bacteroidales fecal indicator bacteria. These methods were used in the analyses of wastewater samples to investigate their feasibility as alternatives to current fecal indicator bacteria culture methods for predicting the efficiency of viral pathogen removal by standard treatment processes. PMA treatment was effective in preventing qPCR detection of target sequences from non-viable cells. Concentrates of small volume, secondary-treated wastewater samples, collected from a publicly owned treatment works (POTW) under normal operating conditions, had little influence on this effectiveness. Higher levels of total suspended solids, such as those associated with normal primary treatment and all treatment stages during storm flow events, appeared to interfere with PMA effectiveness under the sample preparation conditions employed. During normal operating conditions at three different POTWs, greater reductions were observed in PMA-qPCR detectable target sequences of both Enterococcus and Bacteroidales than in total qPCR detectable sequences. These reductions were not as great as those observed for cultivable fecal indicator bacteria in response to wastewater disinfection. Reductions of PMA-qPCR as well as total qPCR detectable target sequences from enterococci and, to a lesser extent, Bacteroidales correlated well with reductions in infectious viruses during both normal and storm flow operating conditions and therefore may have predictive value in determining the efficiency at which these pathogens are removed.