title: Fate of Escherichia coli O157:H7 in field-inoculated lettuce.
abstract: Impact of drip and overhead sprinkler irrigation on the persistence of attenuated Escherichia coli O157:H7 in the lettuce phyllosphere was investigated using a split-plot design in four field trials conducted in the Salinas Valley, California, between summer 2007 and fall 2009. Rifampicin-resistant attenuated E. coli O157:H7 ATCC 700728 (BLS1) was inoculated onto the soil beds after seeding with a backpack sprayer or onto 2- or 4-week-old lettuce plant foliage with a spray bottle at a level of 7 log CFU ml⁻¹. When E. coli O157:H7 was inoculated onto 2-week-old plants, the organism was recovered by enrichment in 1 of 120 or 0 of 240 plants at 21 or 28 days post-inoculation, respectively. For the four trials where inoculum was applied to 4-week-old plants, the population size of E. coli O157:H7 declined rapidly and by day 7, counts were near or below the limit of detection (10 cells per plant) for 82% or more of the samples. However, in 3 out 4 field trials E. coli O157:H7 was still detected in lettuce plants by enrichment 4-weeks post-inoculation. Neither drip nor overhead sprinkler irrigation consistently influenced the survival of E. coli O157:H7 on lettuce.
authors.affiliation: Department of Food Science and Technology, University of California, One Shields Ave., Davis, CA 95616-8598, USA.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Moyne
authors.forename: Mysore R
authors.initials: MR
authors.lastname: Sudarshana
authors.forename: Tyann
authors.initials: T
authors.lastname: Blessington
authors.forename: Steven T
authors.initials: ST
authors.lastname: Koike
authors.forename: Michael D
authors.initials: MD
authors.lastname: Cahn
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Harris
mesh_terms: D002140:California; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification; D005506:Food Contamination / Q000032:analysis*; D018545:Lactuca / Q000382:microbiology*; D050296:Microbial Viability