Aeromonas bacteria; why you should monitor them in drinking water.

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Aeromonas spp are a group of bacteria commonly found in water and food samples.

Generally E coli and coliforms are used as indicators of contamination of water supplies. But recent research has shown that Aeromonas spp are equally important as a measure of water quality because they are implicated in a range of diseases of animals and humans.

For example Aeromonas spp are implicated in gastroenteritis and many infections in humans even though they may not in all cases be the cause of the problem. Infections in wounds caused by injury etc often result from contact with Aeromonas contaminated water. Relatively common types of conditions caused by some Aeromonas spp include gastrointestinal problems like diarrhoea, and septicaemia and cellulitis. Mostly however, gastrointestinal problems are more likely to occur in people who are more susceptible due to age and other conditions.

Data are now available on relative numbers likely to be found in typical situations. For example more Aeromonas spp are found in polluted water specially sewage polluted water. Generally Aeromonas seem to be indicators of general breakdown of bacteriological quality in water distribution systems.

Because of this some European countries and Canada have set standards for levels of Aeromonas in drinking water and food. Adoption of these standards in other countries has partly been frustrated by lack of simple and reliable tests.

Detection of Aeromonas spp has historically been difficult because they show characteristics when cultured that are very similar to other bacteria including coliforms. For example some of the colonies that look like coliforms on the Easygel plates from Micrology Labs may be Aeromonas spp. They can be distinguished by the Oxidase test but this adds another step and is not very convenient.

But now a simple test has been developed by Micrology Labs and is distributed in Australia by Apps Laboratories. It is the ECA check method and uses the Membrane Filtration (MF) method. MF is the preferred method for sampling water at the point of use because it produces a reliable estimate of the actual numbers of bacteria in a relatively large sample. When MF plates are incubated all dark blue to black colonies are counted as E. coli (fecal coliform), blue-gray colonies as general coliforms, pink colonies as Aeromonas spp. and green colonies as Salmonella spp. The sum of dark blue - black and blue - gray colonies is total coliforms. Read about this method starting from ECA Check MF kits.

Aeromonas spp can be reduced significantly by filtration methods in like slow sand filtration but other methods like activated carbon may actually encourage Aeromonas.





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