Persistence of Escherichia coli on Injured Iceberg Lettuce in the Field, Overhead Irrigated with Contaminated Water

Authors: Barker-Reid, Fiona¹; Harapas, Dean²; Engleitner, Siegfried³; Kreidl, Simone²; Holmes, Robert²; Faggian, Robert⁴

Source: Journal of Food Protection®, Volume 72, Number 3, March 2009 , pp. 458-464(7)

Publisher: International Association for Food Protection

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Abstract:

Fresh produce is increasingly implicated in food-related illnesses. Escherichia coli can survive in soil and water and can be transferred onto plant surfaces through farm management practices such as irrigation. A trial was conducted to evaluate the impact of field conditions on E. coli persistence on iceberg lettuce irrigated with contaminated water, and the impact of plant injury on the persistence of E. coli. Lettuce heads were injured at 14, 7, 3, 2, 1, and 0 days before inoculation, with uninjured heads used as a control. All lettuce heads (including controls) were overhead irrigated with a mixture of nonpathogenic E. coli strains (10⁷ CFU/ml). E. coli counts were measured on the day of inoculation and 5 days after, and E. coli was detected on all lettuce head samples. Injury immediately prior to inoculation and harvest significantly (P = 0.00067) increased persistence of E. coli on lettuce plants. Harsh environmental conditions (warm temperatures, limited rainfall) over 5 days resulted in a 2.2-log reduction in E. coli counts on uninjured lettuce plants, and lettuce plants injured more than 2 days prior to inoculation had similar results. Plants with more recent injuries (up to 2 days prior to inoculation) had significantly (P = 7.6 × 10^-6) greater E. coli persistence. Therefore, growers should postpone contaminated water irrigation of lettuce crops with suspected injuries for a minimum of 2 days, or if unavoidable, use the highest microbiological quality of water available, to minimize food safety risks.

Document Type: Research article

Affiliations: 1: Department of Primary Industries, P.O. Box 4166, Parkville, Victoria 3052, Australia;, Email: fiona.barker-reid@dpi.vic.gov.au 2: Department of Primary Industries, 621 Burwood Highway, Knoxfield, Victoria 3180, Australia 3: Department of Primary Industries, 621 Sneydes Road, Werribee, Victoria 3030, Australia 4: Department of Primary Industries, P.O. Box 4166, Parkville, Victoria 3052, Australia

Publication date: 2009-03-01

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First published in 1937, the Journal of Food Protection^®, is a refereed monthly publication. Each issue contains scientific research and authoritative review articles reporting on a variety of topics in food science pertaining to food safety and quality. The Journal is internationally recognized as the leading publication in the field of food microbiology with a readership exceeding 11,000 scientists from 70 countries. The Journal of Food Protection^® is indexed in Index Medicus, Current Contents, BIOSIS, PubMed, Medline, and many others.

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Persistence of Escherichia coli on Injured Iceberg Lettuce in the Field, Overhead Irrigated with Contaminated Water

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