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 stra in designated as O157:H7. Potential health problems could occur if strain O 157:H7 is a more robust survivor in defecated waste than commonly used indi cator bacteria. A laboratory study was conducted to assess E. coli O157:H7 survival relative to a nonpathogenic E. coli strain in two soils with diffe rent physical and chemical characteristics. Bacteria in the inoculated soil s 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 mor tality in the soils. Decay series were described slightly better by a two-s tage function than by a single-stage function. Strain O157:H7 exhibited sim ilar mortality patterns to the nonpathogenic E. coli in the same soil envir onment. Both E. coli strains had greater mortality rates in Pope silt loam (coarse-loamy, mixed, active, mesic Fluventic Dystrudept) than Zanesville s ilt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalf). Difference s in available soil water probably were the overriding factor in E. coli su rvival. Escherichia coli O157:H7 survival could be modeled in the same way as nonpathogenic E. coli and appears to have a slightly higher mortality ra te.