Mortality of Escherichia coli O157:H7 in Two Soils with Different Physical and Chemical Properties

Wild and domesticated animals can harbor a pathogenic Escherichia coli strain designated as O157:H7. Potential health problems could occur if strain O157:H7 is a more robust survivor in defecated waste than commonly used indicator bacteria. A laboratory study was conducted to assess E. coli O157:H7 survival relative to a nonpathogenic E. coli strain in two soils with different physical and chemical characteristics. Bacteria in the inoculated soils were enumerated on a weekly basis for 8 wk using a most probable number (MPN) technique. First-order decay models were used to describe bacteria mortality in the soils. Decay series were described slightly better by a two-stage function than by a single-stage function. Strain O157:H7 exhibited similar mortality patterns to the nonpathogenic E. coli in the same soil environment. Both E. coli strains had greater mortality rates in Pope silt loam (coarse-loamy, mixed, active, mesic Fluventic Dystrudept) than Zanesville silt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalf). Differences in available soil water probably were the overriding factor in E. coli survival. Escherichia coli O157:H7 survival could be modeled in the same way as nonpathogenic E. coli and appears to have a slightly higher mortality rate.