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E. coli as Sole Indicator of Water Pollution Questioned

26 February 2010

E. coli test using a quantitative fluorescent methodIn Ireland, bacterial contamination of water is a national concern, with the Environmental Protection Agency reporting that over 25% of groundwater samples were contaminated with E. coli in the 2004 to 2006 period. E. coli is the most important indicator used in Ireland and its presence indicates water is unfit for human consumption. It has long been thought that E. coli can only survive for short periods of time in the environment, hence its almost universal use as an indicator of recent faecal contamination of waterways.

However, new research investigating pathogen survival in Irish soils conducted by Teagasc Johnstown Castle Environment Research Centre and NUI Galway has found that E. coli can become integrated into the indigenous microbial community in soils and survive for more than nine years, considerably longer than scientists initially thought.

This has important implications for the indicator status of E. coli, suggesting that the presence of E. coli in surface or groundwaters may not be indicative of recent faecal contamination,” explains researcher Fiona Brennan in TResearch, the Teagasc Research and Innovation magazine.

It also suggests that E. coli persistence may be favoured in some soil types and these soils may represent a greater risk of bacterial leaching,” she explains. Research conducted at Johnstown Castle has investigated bacterial transport in grassland soils both in situ at field sites and in field lysimeter (soil monolith) units.

In conjunction with NUI Galway, Teagasc researchers are now using proteomics to investigate the unique properties of E. coli that allow it to persist in the soil for such long periods. Initial findings have found that the environmentally persistent E. coli produce specialised proteins, including ‘cold shock’ and ‘stress response’ proteins, which may assist in the survival and growth of the organism at lower temperatures. E. coli’s ability to survive for prolonged periods of time in soil may compromise its use as the sole indicator of faecal contamination of water.

The full text of this article, which appears in TResearch, the Teagasc Research and Innovation magazine, can be viewed online: http://www.teagascie/publications/tresearch/

This research is funded by Teagasc, IRCSET and SFI, and is a collaborative project between Teagasc and NUI Galway.