Scientists at Environment Canada's National Water Research Institute are developing innovative techniques in a new research area called Microbial Source Tracking.
Millions of Escherichia coli (E. coli) bacteria are found in the intestinal tract of humans and warm-blooded animals. While most of these E. coli are harmless and needed for digestion, their presence in water is an indicator of fecal contamination, and that other disease-causing micro-organisms called pathogens may also be present. High numbers of E. coli may be found after heavy rainfall flushes fecal matter into rivers and lakes.
New techniques are being developed for researchers to compare micro-organisms found in water samples with similar micro-organisms found in potential sources of pollution. For example, do the waterborne E. coli bacteria responsible for closing a beach appear more similar to E. coli from sewage or from Canada geese droppings?
There are a variety of microbial source tracking techniques under investigation. Some are designed to look for specific bacteria in water that are found only in the gut of certain animals. Others are designed to study an indicator micro-organism like E. coli that is found in the gut of many different animals.
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Colonies of E. coli growing on agar petri dish. Photo: Stephen Hill Click to enlarge.
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For example, Antibiotic Resistance Profiling is a technique that is used to compare how E. coli strains grow in the presence of different antibiotics. The assumption is that E. coli from humans have evolved more resistance to those antibiotics used in medical treatments, than E. coli from pets under veterinary treatments, or wildlife species without exposure to any antibiotic treatments. If E. coli from beach waters show a profile of resistance to many antibiotics that is most similar to the profile of resistance for E. coli from pigs, researchers have an indication of where the E. coli is from.
Another technique called DNA fingerprinting compares the DNA between different E. coli strains. In this case, the DNA from one E. coli strain can be chopped up, or sections copied, to produce DNA fragments of different sizes. These fragments can then be separated on a gel into a ladder-like pattern of DNA bands by an electric current. This pattern of DNA fragments can provide a unique DNA fingerprint for an E. coli strain that can be compared to the DNA fingerprint of other E. coli strains. If the DNA fingerprints of E. coli from beach waters are most similar to the DNA fingerprints of E. coli from dogs, researchers have an indication of the source of E. coli.
Knowing where fecal pollution comes from can also help assess potential disease threats. Fecal pollution from human or animal sources can pose different threats since different types of pathogens can be carried in human or animal feces.
While boil-water advisories and beach closures can pose significant hardships and inconveniences for communities, drinking water contaminated with fecal matter can lead to infections and serious gastrointestinal illnesses. Swimming at contaminated beaches can have equally damaging effects and can cause ear infections and rashes.
Most communities across Canada will continue to maintain clean drinking water and safe beaches. Fortunately, new microbial source tracking techniques are on the horizon for areas facing water contamination problems. More scientific research is needed to develop and test these techniques, however preliminary results are encouraging. This knowledge will allow communities to better target clean-up actions, and will hopefully reduce the number of beach closures and boil water advisories in the future.
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