Analysis of the persistence of enteric markers in sewage polluted water on a solid matrix and in liquid suspension

Addressing the persistence of bacterial indicators using qPCR and their respective DNA targets under various conditions is a critical part of risk assessment for water quality monitoring. The goal of this study was to examine the persistence of fecal indicator bacteria (FIB) via Escherichia coli uidA, enterococci 23S rDNA and Bacteroides thetataiotaomicron 1,6 alpha mannanase from cells attached to a solid matrix and in suspension. Raw sewage (10% vol/vol) was seeded into autoclaved river water with half of the sample volume in suspension and the other half was filtered onto membranes and stored at 4 degrees, 27 degrees and 37 degrees C for up to 28 days. At various time points, DNA from cells was extracted, markers were quantified, and were fit to linear and non-linear models (first order exponential, biphasic (double) exponential, two-staged, log-logistic, and Gompertz 3-parameter). First order and biphasic exponential models fit 73% of the experimental data. Persistence increased significantly when the cells were stored in an attached state (p < 0.001). Increasing temperature had an inverse effect on persistence for the cells in suspension. Bacterial cells could be stored on a solid matrix at 4 degrees, 27 degrees and 37 degrees C for up to 27, 18, and 3 days, respectively, with <90% decay. The least stable indicator at 4 degrees, 27 degrees and 37 degrees C was B. thetataiotaomicron in suspension with T-90 = 9.6, 1.8, and 1.1 days, respectively. The most persistent indicator was enterococci, with T-90 > 28 days in an attached state at all temperatures. (C) 2015 Elsevier Ltd. All rights reserved.