Evaluation of methodology for detection and quantification of coliform bacteria and their survival in soil and water
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In Aberdeenshire, approximately 25,000 people rely on potable water from private water supplies. Many of these supplies are of questionable quality with regards to microbiological contamination, which is often due to a lack of maintenance and protection of these supplies. Agricultural practices such as the spreading of slurry and grazing animals in the proximity of supplies all increase the risk of contamination. The presence of coliform bacteria and in particular E. coli, in private water supplies is an indication of the potential for the water supply to be contaminated with pathogenic microorganisms. With the increasing occurrence of severe illness from pathogens such as E. coli O157, which have been found in a number of private water supplies, there is an increasing concern with regards to groundwater quality. This study was conducted initially to determine the magnitude of private water supply contamination in Aberdeenshire and to investigate any links between this contamination with seasonality and rainfall. To enable analysis of a large number of water samples to be carried out within an accepted timeframe, Colilert 18™ was validated for the detection and enumeration of coliform bacteria in potable water and was compared to the accepted standard method, membrane filtration. Colilert 18™ was further validated for use with soil samples to allow the study of factors affecting coliform survival in water and soil to be carried out. Coliform survival in ii soil was found to be influenced particularly by temperature and soil texture. The transport of coliform bacteria in soil was investigated using repacked and undisturbed soil columns, with transport enhanced by rainfall. However even with heavy rainfall coliform bacteria can become attached to or trapped within the soil structure. It was evident from these studies that coliform bacteria and therefore pathogenic microorganisms have the potential to survive in the environment and to travel through the soil structure and enter groundwater.