Investigation of Shiga Toxin-Producing Escherichia coli in Groundwater, River Water, and Fecal Sources in the Kathmandu
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Investigation of Shiga Toxin-Producing Escherichia coli in Groundwater, River Water, and Fecal Sources in the Kathmandu Valley, Nepal Niva Sthapit & Bikash Malla & Rajani Ghaju Shrestha & Sarmila Tandukar & Jeevan B. Sherchand & Eiji Haramoto & Futaba Kazama
Received: 13 July 2020 / Accepted: 3 November 2020 # Springer Nature Switzerland AG 2020
Abstract Shiga toxin-producing Escherichia coli (STEC) is one of the most commonly heard sources of foodborne outbreaks but presently lacks studies of in the Kathmandu Valley. This study explored the presence of STEC in river water (n = 17), groundwater (n = 83), feces (n = 50), and manure (n = 20) in the Kathmandu Valley, Nepal. Samples that were confirmed to be E. coli–positive using the Colilert assay in previous studies were selected to examine the presence of the sfmD, stx1, and stx2 genes using quantitative polymerase chain reaction. Based on Colilert/sfmD gene ratios, the percentage of viable cells of E. coli in the fecal (2.0% ± 2.5%), manure (0.1% ± 0.1%), river water (3.4% ± 3.1%), and groundwater samples (3.9% ± 5.8%) were determined. The presence of the stx1 gene was observed in the fecal (6%), river water (53%), and groundwater (2%) samples, whereas the stx2 gene was detected in the fecal (8%), manure (5%), and river water (71%) samples. Interestingly, the stx/sfmD gene ratios in the groundwater samples were greater than 100%, suggesting the presence of other stx1/stx2-harboring mi-
N. Sthapit Department of Engineering, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan B. Malla : R. Ghaju Shrestha : S. Tandukar : E. Haramoto (*) : F. Kazama Interdisciplinary Center for River Basin Environment, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan e-mail: [email protected] J. B. Sherchand Institute of Medicine, Tribhuvan University, Maharajgunj, Kathmandu 1524, Nepal
croorganisms. These findings indicated the importance of continuing investigation into waterborne sources of STEC contamination within the Kathmandu Valley. Keywords Escherichia coli . Fecal contamination . Groundwater . Nepal . River water . Shiga toxin
1 Introduction Escherichia coli is one of the most ubiquitous bacteria in the environment. E. coli is a gram-negative facultatively anaerobic rod-shaped bacterium residing in the intestines of both humans and animals (Feng et al. 2018). Therefore, these enteric bacteria are traditionally used as a fecal indicator in drinking water (Ishii and Sadowsky 2008). Certain strains of E. coli, such as the diarrheagenic E. coli, have also been known to cause enteric diseases (Wang et al. 2017). Diarrhea is a frequently diagnosed illness caused by a variety of etiologic agents. In 2008, diarrhea was the fifth-highest cause of mortalities (4.3%) in the world (World Health Organization 2012). Additionally, diarrheal diseases are the second leading cause of death in children under 5 years old, particularly in developing countries (World Health Organization 2017). Nepal is a developing country where diarrhea and acute respiratory infections
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