Assessing the role of physicochemical and biochemical soil characteristics on Escherichia coli attachment

Guillaume Paternostre

Food-borne diseases remain a persistent challenge to public health, causing approximately 76 million illnesses and 5,000 deaths every year in the United States (Mead, 1999). The number of incidents has more than doubled since 1987 (Tauxe et al., 1997). Consumption of produce contaminated with pathogenic bacteria, such as Escherichia coli O157:H7, is the primary cause of reported food-borne disease. Agricultural animals, such as cattle and poultry, appear to be one of the most significant sources of pathogens in surface waters (Guber et al., 2005; Ling et al., 2005). Pathogens are shed in feces and can then be spread to humans either by direct consumption of the water or by consumption of crops or vegetables contaminated through irrigation. Bacterial attachment to soil particles plays an important role in the fate and transport of pathogenic bacteria. The objective of this study was to assess the role of physicochemical and biochemical soil characteristics on attachment of a non-pathogenic E. coli strain. E. coli are commonly used as indicators of fecal contamination and can be used to simulate the fate and transport of the pathogenic E. coli O157:H7 strain. The first portion of this study was to compare and contrast the physical, chemical and biochemical characteristics of six soils representative of those found across the State of Washington. The soils displayed a wide range of characteristics, including but not limited to texture, pH, organic content, cation exchange capacity (CEC) and microbial community indicators. The second portion of the study examined E. coli attachment to these characterized soils using batch equilibrium experiments. E. coli was added to 1g of soil and shaken until attachment equilibrium was reached. Soil suspensions were then separated by centrifugation. The amount of E. coli sorbed was calculated as the difference between the bacterial population initially present in solution and the population present after the batch experiment. The Freundlich isotherm presented a representative model for E. coli attachment to each of the soils (R2 > 0.94). E. coli attachment capacity differed across the soils. Among the parameters studied, the bacterial to fungal ratio (r2 = 0.92), total organic carbon content (r2 = 0.87), clay percentage (r2 = 0.86) and soil pH (r2 = 0.84) appeared to be the characteristics with the greatest influence on attachment. These findings suggest conditions that promote E. coli attachment to soil particles, which has implications on development of best management practices (BMPs) to protect surface waters from contamination

Assessing the role of physicochemical and biochemical soil characteristics on Escherichia coli attachment

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