Contamination of Potable Water Distribution Systems by Multiantimicrobial-Resistant Enterohemorrhagic Escherichia Coli
Ram, Siya, Vajpayee, Poornima, Shanker, Rishi, Environmental Health Perspectives
Escherichia coli, a normal inhabitant of the gastrointestinal tract of warm-blooded animals, is used as an indicator of water quality. Certain serotypes have been associated with waterborne disease outbreaks and mortality in humans (Bruneau et al. 2004). Shiga toxin-producing E. coli (STEC) or enterohemorrhagic E. coli (EHEC) are asymptomatic in animals, but human infections may lead to hemorrhagic colitis, hemolytic uremic syndrome, or death (Shelton et al. 2006). Although cattle represent the main reservoir, EHEC is harbored by a wide range of animals and birds (Williams et al. 2006). EHEC causes diseases in humans through production of one or more shiga-like toxins (encoded by stx1 and stx2 and their variants), which inhibit protein synthesis of host cells, leading to cell death. Other virulence factors include the eaeA gene-encoding intimin, responsible for attaching and effacing lesions, and the hlyA gene, which acts as a pore-forming cytolysin on eukaryotic cells. The ingestion of as few as 1-10 EHEC cells may cause illness in humans (Chart 2000; Kuhnert et al. 2000). EHEC contamination of drinking water (processed and unprocessed) has been associated with disease outbreaks (Ashbolt 2004).
In India and some other countries, surface waters from rivers, lakes, and ponds are processed by alum treatment, filtration, and chlorination to be used as drinking water (Clever et al. 2000; Shrivastava et al. 2004). Some recent studies found multiantimicrobial-resistant E. coli isolates positive for virulence determinants for EHEC in surface waters that are being used as raw water to supply drinking water (Hamner et al. 2007; Ram and Shanker 2005; Ram et al. 2007). The occurrence of potential EHEC from extensively used source waters is an important health concern because much of India's population depends on processed or unprocessed surface waters for drinking. Recently, insufficient treatment of surface waters for the drinking water supply, malfunctioning of sewage collection systems, and defective water distribution pipelines have led to contamination of potable water by fecal coliform and other pathogenic bacteria (Babu and Kumar 2002; Bhatta et al. 2007; Shrivastava et al. 2004). However, despite a high incidence of waterborne diseases in India, the potable water supply has never been investigated for the presence of specific pathotypes of diarrheagenic E. coli including EHEC. In India, EHEC has been underacknowledged as far as public health is concerned (Hamner et al. 2007), and thus no report has been published on the presence of multiantimicrobial-resistant E. coli exhibiting virulence determinants specific to EHEC in potable water in India. In this article, we report on the occurrence of multiantimicrobial-resistant E. coli harboring virulence markers of EHEC in potable water samples collected from the drinking water distribution systems of northern India.
Materials and Methods
Sample collection and quantitative enumeration of coliform population. The River Gomti passes through Lucknow, India, and is the main source of drinking water for the city. Water is pumped from the river at Gaughat, which is outside the city, and is sent through a pipeline to Lucknow Jal Sansthan, Aishbagh, 4 km away (Figure 1), where the water is purified by alum treatment, filtration, and chlorination before being released into the drinking water supply (Shrivastava et al. 2004). To test the possibility of the contamination of potable waters by EHEC due to defective water distribution systems and insufficient treatment during production, we collected water samples (1 L) in triplicate for isolation of E. coli and quantitative enumeration of the coliform population (by the multiple-tube fermentation technique) at six sites: site 1, Aishbagh Waterworks (before water enters the distribution system); site 2, Charbagh Loco Thana; site 3, Hussainganj; site 4, Kaiserbagh (water-distribution pipeline that neither percolated nor ran along open drainage); site 5, Hazaratganj; site 6, Charbagh Railway Station (pipeline that percolated and ran along open drainage) (Figure 1). …