Abstract
Taihu Lake is one of the largest freshwater lakes in China, serving as an important source of drinking water; >60% of source water to this lake is provided by the Tiaoxi River. This river faces serious fecal contamination issues, and therefore, a comprehensive investigation to identify the sources of fecal contamination was carried out and is presented here. The performance of existing universal (BacUni and GenBac), human (HF183-Taqman, HF183-SYBR, BacHum, and Hum2), swine (Pig-2-Bac), ruminant (BacCow), and avian (AV4143 and GFD) associated microbial source tracking (MST) markers was evaluated prior to their application in this region. The specificity and sensitivity results indicated that BacUni, HF183-TaqMan, Pig-2-Bac, and GFD assays are the most suitable in identifying human and animal fecal contamination. Therefore, these markers along with marker genes specific to selected bacterial pathogens were quantified in water and sediment samples of the Tiaoxi River, collected from 15 locations over three seasons during 2014 and 2015. Total/universal Bacteroidales markers were detected in all water and sediment samples (mean concentration 6.22 log10 gene copies/100 ml and 6.11 log10 gene copies/gram, respectively), however, the detection of host-associated MST markers varied. Human and avian markers were the most frequently detected in water samples (97 and 89%, respectively), whereas in sediment samples, only human-associated markers were detected more often (86%) than swine (64%) and avian (8.8%) markers. The results indicate that several locations in the Tiaoxi River are heavily polluted by fecal contamination and this correlated well with land use patterns. Among the five bacterial pathogens tested, Shigella spp. and Campylobacter jejuni were the most frequently detected pathogens in water (60% and 62%, respectively) and sediment samples (91% and 53%, respectively). Shiga toxin-producing Escherichia coli (STEC) and pathogenic Leptospira spp. were less frequently detected in water samples (55% and 33%, respectively) and sediment samples (51% and 13%, respectively), whereas E. coli O157:H7 was only detected in sediment samples (11%). Overall, the higher prevalence and concentrations of Campylobacter jejuni, Shigella spp., and STEC, along with the MST marker detection at a number of locations in the Tiaoxi River, indicates poor water quality and a significant human health risk associated with this watercourse. GRAPHICAL ABSTRACTTracking fecal contamination and pathogens in watersheds using molecular methods.
Highlights
Fecal contamination of drinking water sources, harvestable shellfish, and recreational waters is a major concern of public health, as it promotes human exposure to pathogenic microorganisms (Napier et al, 2017)
Among the LI-microbial source tracking (MST) methods, Bacteroidales are often used as the target, as they are obligate anaerobic bacteria found in the human and animal gut at higher levels than E. coli (Bernhard and Field, 2000); host-associated Bacteroidales 16S rRNA gene markers have been developed for different hosts to discriminate between human and other animal fecal sources in the environment (Kildare et al, 2007; Shanks et al, 2008; Mieszkin et al, 2009; Raith et al, 2013; Green et al, 2014)
Our MST quantitative PCR (qPCR) validation study demonstrates that BacUni, HF183 Taqman, Pig-2-Bac, and GFD assays are the most suitable for differentially identifying and monitoring human and animal fecal contamination in the Taihu watershed
Summary
Fecal contamination of drinking water sources, harvestable shellfish, and recreational waters is a major concern of public health, as it promotes human exposure to pathogenic microorganisms (Napier et al, 2017). Fecal indicator bacteria (FIB) have been used to monitor pollution in environmental waters and to assess the associated public health risks (Griffith et al, 2009). The major limiting factor, is that FIB detection does not indicate the source or origin of fecal contamination (Field and Samadpour, 2007), which is crucial for the characterization of a public health risk and the implementation of remediation measures. Microbial source tracking (MST) techniques have been developed over the last decade to unequivocally identify the sources and origins of fecal pollution Both library-dependent (LD-MST) and library-independent MST (LI-MST) methods are available for identifying the source of fecal pollution, LD-MST methods have several limitations in correctly assigning fecal contamination to host-specific sources (Harwood et al, 2003; Field and Samadpour, 2007). It has recently been reported that avian feces could be better distinguished from other fecal sources by targeting bacterial taxonomic groups such as Helicobacter spp., rather than Bacteroidales 16S rRNA (Green et al, 2012)
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