title: Tracing enteric pathogen contamination in sub-Saharan African groundwater.
abstract: Quantitative PCR (qPCR) can rapidly screen for an array of faecally-derived bacteria, which can be employed as tracers to understand groundwater vulnerability to faecal contamination. A microbial DNA qPCR array was used to examine 45 bacterial targets, potentially relating to enteric pathogens, in 22 groundwater supplies beneath the city of Kabwe, Zambia in both the dry and subsequent wet season. Thermotolerant (faecal) coliforms, sanitary risks, and tryptophan-like fluorescence, an emerging real-time reagentless faecal indicator, were also concurrently investigated. There was evidence for the presence of enteric bacterial contamination, through the detection of species and group specific 16S rRNA gene fragments, in 72% of supplies where sufficient DNA was available for qPCR analysis. DNA from the opportunistic pathogen Citrobacter freundii was most prevalent (69% analysed samples), with Vibrio cholerae also perennially persistent in groundwater (41% analysed samples). DNA from other species such as Bifidobacterium longum and Arcobacter butzleri was more seasonally transient. Bacterial DNA markers were most common in shallow hand-dug wells in laterite/saprolite implicating rapid subsurface pathways and vulnerability to pollution at the surface. Boreholes into the underlying dolomites were also contaminated beneath the city highlighting that a laterite/saprolite overburden, as occurs across much of sub-Saharan aquifer, does not adequately protect underlying bedrock groundwater resources. Nevertheless, peri-urban boreholes all tested negative establishing there is limited subsurface lateral transport of enteric bacteria outside the city limits. Thermotolerant coliforms were present in 97% of sites contaminated with enteric bacterial DNA markers. Furthermore, tryptophan-like fluorescence was also demonstrated as an effective indicator and was in excess of 1.4μg/L in all contaminated sites.
authors.affiliation: British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK. Electronic address: jare1@bgs.ac.uk.
authors.forename: J P R
authors.initials: JP
authors.lastname: Sorensen
authors.affiliation: British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Lapworth
authors.affiliation: Centre of Ecology and Hydrology, Maclean Building, Wallingford OX10 8BB, UK.
authors.forename: D S
authors.initials: DS
authors.lastname: Read
authors.affiliation: University of Zambia, Great East Road Campus, P.O. Box 32379, Lusaka, Zambia.
authors.forename: D C W
authors.initials: DC
authors.lastname: Nkhuwa
authors.affiliation: British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Bell
authors.affiliation: Lukanga Water and Sewerage Company Limited, P.O. Box 81745, Kabwe, Zambia.
authors.forename: M
authors.initials: M
authors.lastname: Chibesa
authors.affiliation: University of Zambia, Great East Road Campus, P.O. Box 32379, Lusaka, Zambia.
authors.forename: M
authors.initials: M
authors.lastname: Chirwa
authors.affiliation: University of Zambia, Great East Road Campus, P.O. Box 32379, Lusaka, Zambia.
authors.forename: J
authors.initials: J
authors.lastname: Kabika
authors.affiliation: Lukanga Water and Sewerage Company Limited, P.O. Box 81745, Kabwe, Zambia.
authors.forename: M
authors.initials: M
authors.lastname: Liemisa
authors.affiliation: Department of Civil and Environmental Engineering, University of Surrey, Guildford, GU2 7XH, UK.
authors.forename: S
authors.initials: S
authors.lastname: Pedley
mesh_terms: D017954:Africa South of the Sahara; D004755:Enterobacteriaceae / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D004784:Environmental Monitoring; D060587:Groundwater / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S; D014871:Water Microbiology
chemical_list: D012336:RNA, Ribosomal, 16S
keywords: Enteric bacterial pathogens; Quantitative PCR; Sub-Saharan Africa; Thermotolerant coliforms; Tryptophan-like fluorescence; Urban