Investigation of Shiga Toxin-Producing Escherichia coli in Groundwater, River Water, and Fecal Sources in the Kathmandu Valley, Nepal

Occurrence and Reduction of Shiga Toxin-Producing Escherichia coli in Wastewaters in the Kathmandu Valley, Nepal

“…The remaining microbiome and nutrients in the effluent may also encourage the increase in pathogenic bacteria in the environment [22]. A previous study also detected the presence in groundwater, river water, feces, and manure in the Kathmandu Valley, and suggested the possibility of river water contamination from wastewater discharge and river water and groundwater interactions near the river channels contributing to groundwater contamination [23].…”

“…Based on the results obtained in this study, the higher concentrations of the stx2 gene than the stx1 in the wastewaters suggest the growing presence of aggressive STEC infection in the population of the Kathmandu Valley and should be a public health concern. This is especially true due to the trail of the wastewater effluent discharged into the river water, which is reclaimed for irrigational purposes and interacts with groundwater by the river banks used for household use too, as previously discussed [23].…”

“…As described in previous studies [23,38,39], the E. coli concentrations were determined in 100 mL wastewater for dilutions of 10 −2 , 10 −4 , and 10 −6 using the Colilert Quanti-Tray 2000 (IDEXX Laboratories, Westbrook, USA). However, in this study, an additional bottle of 100 mL sample diluted to 10 −2 was also directly incubated at 37 • C for 24 h. In the Quanti-Tray, the wells that fluoresced blue under the UV lamp were considered positive for E. coli.…”

“…To evaluate the performance of the heat DNA extraction method, 10 −1 and 10 −2 dilutions of E. coli K-12 (NBRC3301, National Institute of Technology and Evaluation, Kisarazu, Japan) were prepared in 100 mL autoclaved ultrapure water. Following the manufacturer's instructions, these samples were subjected to the Colilert-18 test kit (IDEXX Laboratories, Westbrook, ME, USA) [23,38,39]. On the Quanti-Tray 2000 (IDEXX Laboratories), wells that appeared yellow and blue under UV light were punctured using a micropipette to collect 500 µL from eight large positive wells and four small positive wells of the 10 −1 tray and from eight large positive wells and six small positive wells of the 10 −2 tray.…”

“…Presently, only 88% of households in the Kathmandu Valley possess sewage facilities, and 11% of households still use a septic tank or pit [24]. There are currently five WWTPs in the Kathmandu Valley, of which only one WWTP was in operation (activated sludge system) and the remaining four WWTPs (aerated and non-aerated lagoons) were either under partial operation or non-functional during the time of sampling [5,23,25]. The status "partially operating" shows the inability to treat the wastewater as effectively as a fully functional treatment plant owing to poor operation, maintenance, and management [5].…”