Persistence of <i>Escherichia coli</i> O157:H7 in soil and on plant roots

<jats:title>Summary</jats:title> <jats:p> Soil microcosms were inoculated with <jats:italic>Escherichia coli</jats:italic> O157:H7 to test persistence in fallow soil, on roots of cover crops and in presence of manure. In fallow soils, <jats:italic>E. coli</jats:italic> O157:H7 persisted for 25–41 days, on rye roots for 47–96 days and on alfalfa roots, in a silt loam soil, for 92 days whereas on other legumes persistence ranged from 25–40 days, similar to fallow soil. Manure did not seem to affect the persistence of <jats:italic>E. coli</jats:italic> O157:H7 in these soils. Indigenous and manure‐applied coliform populations often decreased faster when <jats:italic>E. coli</jats:italic> O157:H7 was applied, indicating possible competition between microflora. Coliform populations in microcosms not inoculated with <jats:italic>E. coli</jats:italic> O157:H7 decreased more slowly or increased. Microbial community analyses showed little effect for <jats:italic>E. coli</jats:italic> O157:H7 inoculation or addition of manure. Microbial community metabolic activity was enhanced from rye roots after 14 days and by 63 days from alfalfa roots. Microbial community lactose utilization increased over time on rye roots in all soils and on alfalfa roots in a silt loam soil when <jats:italic>E. coli</jats:italic> O157:H7 was inoculated. Lactose utilization also increased for uninoculated rye roots, soil around rye roots and in some fallow soils. Our data suggest that clay increases persistence and activity of <jats:italic>E. coli</jats:italic> O157:H7 and other coliforms. In frozen soil stored for over 500 days, <jats:italic>E. coli</jats:italic> O157:H7 was viable in 37% of tested samples. In summary, <jats:italic>E. coli</jats:italic> O157:H7 persisted longer and activity was enhanced with some cover crops in these soils due to plant roots, the presence of clay and freezing. </jats:p>