Abstract
Riverbed sediment is a vital component of river ecosystems and plays an important role in many geomorphological and ecological processes. However, when re-suspension occurs, pathogenic bacteria associated with sediment particles may be released into the water column, thus creating a health risk to those who use such water for drinking, household and recreational purposes. The aim of this study was to investigate the presence of bacterial pathogens Salmonella spp. and Shigella spp. in the Apies River and to ascertain whether there was any level of genetic relatedness between river water and riverbed sediment isolates of these pathogenic bacteria. A total of 124 water and sediment samples were collected from a site located on the Apies Rivers upstream of the Daspoort Wastewater Treatment Works, Pretoria, Gauteng, South Africa, between August and November 2014. In order to detect and identify the target bacteria, samples were analysed by culture-dependent and culture-independent techniques (quantitative real-time PCR). Genetic relatedness was established using Sanger sequencing of the invA gene of Salmonella spp. and ipaH of Shigella spp. Results of this study displayed the presence of the target bacteria both in the water and sediment of the river. The phylogenetic tree of Salmonella spp. revealed a ≥ 99% and 99% genetic relatedness between river water and riverbed sediment isolates for Salmonella spp. and Shigella spp., respectively. The degree of genetic relatedness between sediment and water pathogen isolates suggests that these organisms could possibly have a common origin and that there could be possible movement of microorganisms between the water column and the sediments. Keywords: Salmonella spp., Shigella spp., river water, riverbed sediment, genetic relatedness
Highlights
Many waterborne pandemics are associated with Shigella spp. and Salmonella spp. (Threlfall, 2002)
The aim of the present study was to establish the genetic relatedness between Salmonella spp. and Shigella spp. isolated from water and those isolated from riverbed sediments of the Apies River using culture-based and culture-independent methods in a bid to understand genetic similarity among isolates of water and sediments
Culture counts of Salmonella spp. and Shigella spp. in water were respectively in the range of zero (9.6%) to 2.98 log10 colony-forming units (CFU)/100 mL and 2.93 to 3.16 log10 CFU/100 mL, while in the sediment samples the counts were in the range of 4.70 to 4.91 log10 CFU/100 mL for Salmonella spp. and 4.78 to 4.92 log10 CFU/100 mL for Shigella spp
Summary
Many waterborne pandemics are associated with Shigella spp. and Salmonella spp. (Threlfall, 2002). All four species are responsible for shigellosis or bacillary dysentery, a disease that causes high fever, neurological disturbances and mucus-pyo-hemorrhagic dysentery (Sansonetti, 2001). The presence of Shigella spp. in drinking water indicates human faecal contamination. This bacterium is of fundamental public health significance because of its great pathogenicity. Outbreaks of shigellosis have been associated with water treatment failures (at times inefficient treatment) in water supply systems (Karanis et al, 2007). Such waterborne outbreaks often lead to a considerable number of individuals being simultaneously affected, and in most cases the outbreak subsides when the water supply is adequately treated (Pillsbury, 2010)
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