title: Transfer of Escherichia coli O157:H7 from simulated wildlife scat onto romaine lettuce during foliar irrigation.
abstract: A field trial in Salinas Valley, California, was conducted during July 2011 to quantify the microbial load that transfers from wildlife feces onto nearby lettuce during foliar irrigation. Romaine lettuce was grown using standard commercial practices and irrigated using an impact sprinkler design. Five grams of rabbit feces was spiked with 1.29 × 10(8) CFU of Escherichia coli O157:H7 and placed - 3, - 2, and - 1 days and immediately before a 2-h irrigation event. Immediately after irrigation, 168 heads of lettuce ranging from ca. 23 to 69 cm (from 9 to 27 in.) from the fecal deposits were collected, and the concentration of E. coli O157:H7 was determined. Thirty-eight percent of the collected lettuce heads had detectable E. coli O157:H7, ranging from 1 MPN to 2.30 × 10(5) MPN per head and a mean concentration of 7.37 × 10(3) MPN per head. Based on this weighted arithmetic mean concentration of 7.37 × 10(3) MPN of bacteria per positive head, only 0.00573% of the original 5 g of scat with its mean load of 1.29 × 10(8) CFU was transferred to the positive heads of lettuce. Bacterial contamination was limited to the outer leaves of lettuce. In addition, factors associated with the transfer of E. coli O157:H7 from scat to lettuce were distance between the scat and lettuce, age of scat before irrigation, and mean distance between scat and the irrigation sprinkler heads. This study quantified the transfer coefficient between scat and adjacent heads of lettuce as a function of irrigation. The data can be used to populate a quantitative produce risk assessment model for E. coli O157:H7 in romaine lettuce to inform risk management and food safety policies.
authors.affiliation: Western Center for Food Safety, University of California at Davis, 1477 Drew Avenue, Suite 101, Davis, California 95618, USA. ratwill@ucdavis.edu.
authors.forename: Edward R
authors.initials: ER
authors.lastname: Atwill
authors.affiliation: Western Center for Food Safety, University of California at Davis, 1477 Drew Avenue, Suite 101, Davis, California 95618, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Chase
authors.affiliation: Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 5100 Paint Branch Parkway, College Park, Maryland 20740, USA.
authors.forename: David
authors.initials: D
authors.lastname: Oryang
authors.affiliation: Western Center for Food Safety, University of California at Davis, 1477 Drew Avenue, Suite 101, Davis, California 95618, USA.
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Bond
authors.affiliation: University of California Cooperative Extension Monterey County, 1432 Abbott Street, Salinas, California 93901, USA.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Koike
authors.affiliation: University of California Cooperative Extension Monterey County, 1432 Abbott Street, Salinas, California 93901, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Cahn
authors.affiliation: RTI International, 3040 East Cornwallis Road, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Maren
authors.initials: M
authors.lastname: Anderson
authors.affiliation: RTI International, 3040 East Cornwallis Road, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Amirhossein
authors.initials: A
authors.lastname: Mokhtari
authors.affiliation: Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 5100 Paint Branch Parkway, College Park, Maryland 20740, USA.
authors.forename: Sherri
authors.initials: S
authors.lastname: Dennis
mesh_terms: D000818:Animals; D000835:Animals, Wild; D002140:California; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D059022:Food Safety; D018545:Lactuca / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology