title: Comparative examination of Escherichia coli O157:H7 survival on romaine lettuce and in soil at two independent experimental sites.
abstract: Little is known about the influence of abiotic factors such as climate and soil chemistry on the survival of Escherichia coli O157:H7 in field lettuce. We applied a nalidixic acid-resistant derivative of strain ATCC 700728 to field-grown romaine lettuce in two regions in Canada characterized by large variances in soil type and climate. Surviving populations in soil and on lettuce leaves were estimated on sorbitol MacConkey agar supplemented with nalidixic acid. Data were fitted with the Weibull decline function to permit comparison of decay rates in the two experimental sites. E. coli O157:H7 populations fell from 10⁵ to <10² CFU/g on leaves, and <10³ CFU/g in soil within 7 days after inoculation. Analysis revealed there was no significant difference between decay rates at the two experimental sites in either environment. The results of this study suggest that the inherent ecological fitness of E. coli O157:H7 ATCC 700728 determines the extent of survival in the production environment.
authors.affiliation: Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre, 32 Main Street, Kentville, Nova Scotia B4N 1J5, Canada. greg.bezanson@agr.gc.ca
authors.forename: Greg
authors.initials: G
authors.lastname: Bezanson
authors.forename: Pascal
authors.initials: P
authors.lastname: Delaquis
authors.forename: Susan
authors.initials: S
authors.lastname: Bach
authors.forename: Robin
authors.initials: R
authors.lastname: McKellar
authors.forename: Ed
authors.initials: E
authors.lastname: Topp
authors.forename: Alex
authors.initials: A
authors.lastname: Gill
authors.forename: Burton
authors.initials: B
authors.lastname: Blais
authors.forename: Matthew
authors.initials: M
authors.lastname: Gilmour
mesh_terms: D002980:Climate; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000254:growth & development*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D007700:Kinetics; D018545:Lactuca / Q000382:microbiology*; D050296:Microbial Viability; D012988:Soil Microbiology