Assessment of the decay rates of microbial source tracking molecular markers and faecal indicator bacteria from different sources

Abstract

Aims Evaluate the T90 and compare the decay of different faecal indicator bacteria (FIB) and molecular microbial source tracking (MST) markers of human and animal sources during summer and winter. Methods and Results The persistence of Escherichia coli and enterococci and several MST molecular markers targeting host-specific Bifidobacterium and Bacteroidales species (BifHM, BifCW, BifPL, HF183/BFD, Rum2Bac and Pig2Bac) was assessed at the same time using mesocosms. Dialysis bags filled with diluted wastewater from different sources were kept in an outdoor water tank and monitored regularly to assess the inactivation rates. The T90 values of E. coli by culture methods ranged from 1·52 to 5·69 days in summer and 2·06 to 6·19 days in winter, whereas with qPCR 2·29-4·23 days in summer and 4·17-8·09 days in winter. T90 values for enterocci ranged from 1·15 to 3·10 days in summer and from 3·01 to 5·46 days in winter. Significant differences were observed between faecal sources for both markers. For the MST makers similar T90 values were obtained in summer (1·05-1·91 days), whereas higher variability was observed in winter (2·90-6·12 days). Conclusions Different decay rates were observed for the FIB from the different sources, especially for E. coli in ruminant samples. A higher variability among T90 values of the different MST markers in winter was observed, whereas similar T90 values were detected in summer highlighting the stronger effect of environmental parameters during this season. Significance and Impact of the Study The diverse inactivation rates observed in bacteria from different faecal sources have implications when these rates are used to model faecal pollution in water. The use of FIBT90 of different sources is essential to develop reliable predictive models. Since different inactivation of E. coli regarding the source of pollution has been observed, the source of the pollution has to be considered for modelling approaches.