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Title: Application of microbial source tracking techniques to characterize fecal pollution entering Taihu Lake (China)
Author: Vadde, K. K.
ISNI:       0000 0004 7659 0334
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Contamination of water bodies with human and animal fecal sources could significantly affect human health by disseminating pathogenic microorganisms. Therefore, accurate identification of sources that contribute to fecal pollution is vital for executing effective management strategies. Microbial source tracking (MST) is a promising approach to identify the sources of fecal contamination, which could be valuable for best management practices. The waterbody of interest, Taihu Lake, is one of the largest freshwater Lakes in China and serves as an important source for drinking water in addition to many other roles. Though this Lake is connected to several Rivers, Tiaoxi River provides most of the inflow (>60%). Previous reports indicated that Tiaoxi river is facing serious issues with fecal contamination and suggested implementing MST study. In this regard, 25 sampling locations were selected across the Tiaoxi River to monitor fecal contamination, and samples (water and sediment) were collected in three seasons (autumn 2014, winter and summer 2015). Physico-chemical and culture-based microbiological analysis of water samples were carried out for preliminary assessment of fecal contamination at these locations. The results showed that TN, TP, NO2-N, and NH4-N were the major nutrients that contributed to pollution in this River, and fecal coliform counts were high (>250 CFU/100 mL) in 15 locations indicating that a MST study was needed to ascertain sources of fecal contamination. Before applying MST, microbial community analysis was carried out in 45 water samples (collected from 15 locations in three seasons) to identify the diversity and composition of bacteria, including fecal and pathogenic bacteria, using Illumina high throughput sequencing. The Operational Taxonomic Units (OTUs) data comparison between total water samples with individual fecal sources indicated that chicken (9.8%), pig (7.1%), and human fecal samples (4.5%) have shared OTUs with total water samples, indicating the presence of avian, pig and human fecal contamination in this River. The genus level bacterial community data revealed that members of five fecal associated genera (Bacteroides, Prevotella, Blautia, Faecalibacterium, and Dorea) were present at several locations, pointing to human or animal fecal contamination in those locations. Furthermore, seven potential pathogenic bacterial genera namely Acinetobacter, Aeromonas, Arcobacter, Brevundimonas, Enterococcus, Escherichia-Shigella, and Streptococcus were also detected with high relative abundance (>0.1%), specific PCR assays are needed for accurate identification of their pathogenicity. As MST validation is required prior to its application in any new geographical area, a comprehensive evaluation of ten MST assays including two universal/general Bacteroidales (BacUni and GenBac3), four human-associated (HF183 SYBR, HF183 Taqman, BacHum and Hum2), one swine associated (Pig-2-Bac), one livestock/domestic animal associated (BacCow) and two avian associated MST qPCR assays (GFD and AV4143) targeting sewage, human and animal fecal DNA was carried out to determine the suitable MST assays for identifying fecal pollution sources at Taihu watershed. The results showed that BacUni, HF183 Taqman, Pig-2-Bac and GFD markers were the best performers and are recommended for tracking total and host-associated fecal contamination in this region. The above evaluated MST markers were quantified in 15 locations (in water and sediment samples) of Tiaoxi River. Total Bacteroidales marker was detected in all the water and sediment samples, confirming the presence of fecal contamination. The human-associated marker was frequently detected at four locations at high concentrations (4.83-5.62 log10 copies/100ml) indicating that those locations were heavily contaminated with fecal pollution. Swine associated marker was frequently detected in samples from two locations and the avian associated marker was detected with high concentrations at 4 locations, correlating with the land use patterns and pointing to the entry of pig and avian fecal sources into Tiaoxi River. Among five bacterial pathogens monitored, Campylobacter jejuni was detected exceeding levels of lowest infection dose in 2 locations that are highly polluted with avian fecal source. Similarly, Shigella spp. were detected at two locations that are highly contaminated with human fecal sources, and Shiga toxin producing E.coli (STEC) at 2 locations that are contaminated with either human or pig fecal sources. The bacterial pathogen quantification results correlate with the findings of host associated fecal markers, demonstrating the potential of MST in predicting the presence of pathogenic organisms and the concomitant risk to human health.
Supervisor: Raju, Sekar ; McCarthy, Alan ; Rong, Rong Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral