Microbial Indicators and Pathogens in our water: where they come from and what they do

Contamination of drinking water and recreational waters with faecal microorganisms is of high public interest, with billions spent annually managing, preventing or treating this contamination. Globally contaminated water kills an estimated 1-2 million annually and in New Zealand it has been estimated that 100,000 become sick each year from waterborne microorganisms. The organisms causing disease include bacteria such as Campylobacter jejuni, E. coli O157, and Salmonella; protozoa such as Cryptosporidium and Giardia; and viruses such as norovirus and adenovirus. People who are infected suffer a range of illnesses, which can include diarrhea, fever, vomiting, reactive arthritis, and more serious complications.

The microbial water quality of our drinking water, and our recreational waters are assessed by measuring levels of the indicator bacteria Escherichia coli and/or enterococci. These bacteria usually do not cause illness themselves, but they are present in the faeces at high levels, and thus are typically associated with pathogens spread by the faecal oral route. These are useful indicators, and water containing these organisms should be treated as though it is contaminated with pathogens and appropriate action taken.

One key action is to identify the source of the contamination. There are a range of approaches which can be taken, but the most popular world-wide is the application of microbial source tracking methodology based on the detection of DNA from organisms specific to faecal sources. Human sewage or faeces is the highest risk source, and a number of markers are available to detect this source. Zoonotic sources of pathogens include cows, sheep, dogs, and wildfowl which again specific DNA markers are available. When a source of pollution is fresh, and dominated by a single source interpretation is relatively straight forward. However, mixed sources of pollution, aged or partially treated sources, and potential confounding non-faecal sources can make this challenging.

All sources of faecal pollution have a health risk associated with them, and a health risk may exist even in the absence of a detectable faecal source. Therefore, a full assessment may require the direct quantitation of pathogens in a water sample and/or a source. Molecular methods are becoming available which can make this more feasible, although there are issues related to sensitivity and specificity of some methods. Particularly where pathogens aren’t detected, there needs to be a robust programme of sampling to ensure this actually reflects the true situation.

We live in a microbial world, and naturally water is an ecosystem for microorganisms. Reducing the disease burdens from contaminated water, requires a thorough understanding of the threat microorganisms can pose, and how changes in the environment or in management practices can tip the balance from safe water into dangerous water.