When thirsty, nothing is as refreshing as a cool glass of water. So you reach out for that glass of water, but what if you paused to think about what you are just about to drink. Water is vital for our health and well being, it constitutes about two-third of our body and the innumerous benefits and importance make it a non-negotiable part of our lives. At the first glance and sniff we know if the water looks clean and odorless then comes the question of microbial contamination, something the naked eye cannot see. Because of the nature of water, its solubility and availability, it can be host to many microbes and become the source of many waterborne diseases. Growing population, industrialization and rapid urbanization has changed the rate of water demand and consumption, consequently water supply.
The need for usable fresh water has required all available water sources, which are rivers, streams, lakes to be put to use. On the other hand, most of the untreated sewage, household, industrial and chemical wastes are also being dumped into these same sources of water, thus polluting them. Most strains of E. coli (Escherichia Coli) are harmless and often beneficial to human, except for E. coli O157:H7, which has emerged as a major cause of waterborne diseases. Enteric viruses are also causative agents of human diseases and cause wide variety of pathological symptoms and enteroviral infections, especially in children. As enteroviral epidemics are predominantly waterborne, water pollution poses immediate threat to human health.  In this article we explore contamination from this particular strain of E. coli bacteria (O157:H7) and enteric viruses, their potential threats and how to test the water for such contamination.
Bacterial contamination of water is usually in the form of coliform bacteria. Coliform bacteria live in soil/vegetation and in the gastrointestinal tract of animals and humans. They thrive in warm, wet and dark places. Coliforms enter water supplies from the direct disposal of waste into streams, lakes or from runoff from wooded areas, pastures, feedlots, septic tanks, and sewage plants into groundwater. In addition to these, coliforms can enter an individual house via backflow of water from a contaminated source, carbon filters, or leaking well caps. Coliform bacteria refer to a group of bacteria, including E. coli. E. coli O157:H7
A particular strain of E.coli known as E. coli O157:H7 causes a severe intestinal infection in humans. It is the most common strain known to cause illness, often severe in people. It can be differentiated from other E. coli by the production of a potent toxin, Verotoxin(VT2 or Shiga-like toxin II)[2 ], that damages the lining of the intestinal wall causing bloody diarrhea. It is also known as enterohemorrhagic E. coli infection. The Centers for Disease Control and Prevention (CDC) reports about 70,000 cases of this type of E. coli infection occur in the United States each year. [3 ]
Viruses are resilient organisms able to withstand high concentrations of NaCl and large changes in temperature. These characteristics allow them to flourish in aquatic environment. Most common viruses involved in contamination are Hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses.
Among the above mentioned viruses enteroviral contaminants are predominantly waterborne. They are usually found in insufficiently treated drinking water, ground water, river/stream, household wastes and infected feces are an exogenous infection source. Recent studies show that swimming in recreational centers and sea- water may also cause vulnerability toward getting infected. Human enteroviruses belong to the Picornaviridae family (pico = SMALL – RNA viruses), Enterovirus genus. Traditional division organizes this taxonomic group into the subgenera polioviruses, coxackieviruses (group A, B), echoviruses and a group of enteroviruses marked according to their serotype number. In 2003, the International Committee on Taxonomy of Viruses created a new taxonomy classification. Enteroviruses from this time forth were divided into 5 groups of species based on their molecular properties (Table. 1). 
Existing and potential threats
Every year, unsafe water, coupled with a lack of basic sanitation, kills at least 1.6 million children under the age of five years – more than eight times the number of people who died in the Asian tsunami of 2004. 
Total coliforms count is the standard by which microbial contamination is measured. Should there be contamination in water coliforms will be one of the first bacteria, and they will be in much larger quantities than pathogenic bacteria, if present. Therefore, coliforms act as indicators, their presence can be taken as an indication that other harmful or pathogenic bacteria are present. A popular and convenient technique is collecting water sample, passing it through a 0.45µm diameter filter to capture any bacteria. The filter is then placed on selected growth media and incubated for 24 hours. Colonies develop; the colonies are then counted either by hand using filter grid or by automated colony counter. After this initial confirmation there are several methods to test for contamination by O157:H7 strain of E. coli.
This particular strain of bacteria does not ferment sorbitol in 24 hours like most other E. coli.  Another method which is much more expensive but more precise is by using PCR (Polymerase Chain Reaction). Using PCR and fluorescent tag, small amounts of bacterial DNA can be traced and then amplified, where newly formed DNA emits fluorescent signal. It takes about two hours and can differentiate between human and non-human E. coli source. The technique which gives the fastest results for coliform presence is by a hand-held portable fluorometric assay kit. It takes ten minutes and uses antibodies tagged with fluorescents to search out desired bacteria. But currently the available antibodies are limited for this kit.
PCR method and cell cultures are used to isolate and identify viruses in condensed and purified water. Selected cell lines are infected and checked for cytopathogenic effect (CPE), which is the assessment of damaged and dead cells. The most commonly used is the cell culture method, where water sample is concentrated and purified and then using molecular techniques virus is isolated in cell culture. Compared to cell culture, PCR technique increases the effectiveness of determining enteroviral inherence in water samples, but the drawback is it still does not give direct information about the contagiosity of pathogens. To remedy this a new method has been devised. Based on the hypothesis that in a cell line where virus has been introduced only the contagious will multiply, the new method integrates PCR and cell culture. After the incubation period, sample of viral genetic material is collected from cell culture and tested with PCR to estimate the presence of enteroviruses. This method is applicable even for cell lines that does not trigger CPE. 
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