Surface and Internalized Escherichia coli O157:H7 on Field-Grown Spinach and Lettuce Treated with Spray-Contaminated Irrigation Water

Authors: Erickson, Marilyn C.¹; Webb, Cathy C.¹; Diaz-Perez, Juan Carlos²; Phatak, Sharad C.²; Silvoy, John J.²; Davey, Lindsey¹; Payton, Alison S.¹; Liao, Jean¹; Ma, Li³; Doyle, Michael P.¹

Source: Journal of Food Protection®, Volume 73, Number 6, June 2010 , pp. 1023-1029(7)

Publisher: International Association for Food Protection

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Abstract:

Numerous field studies have revealed that irrigation water can contaminate the surface of plants; however, the occurrence of pathogen internalization is unclear. This study was conducted to determine the sites of Escherichia coli O157:H7 contamination and its survival when the bacteria were applied through spray irrigation water to either field-grown spinach or lettuce. To differentiate internalized and surface populations, leaves were treated with a surface disinfectant wash before the tissue was ground for analysis of E. coli O157:H7 by direct plate count or enrichment culture. Irrigation water containing E. coli O157:H7 at 10², 10⁴, or 10⁶ CFU/ml was applied to spinach 48 and 69 days after transplantation of seedlings into fields. E. coli O157:H7 was initially detected after application on the surface of plants dosed at 10⁴ CFU/ml (4 of 20 samples) and both on the surface (17 of 20 samples) and internally (5 of 20 samples) of plants dosed at 10⁶ CFU/ml. Seven days postspraying, all spinach leaves tested negative for surface or internal contamination. In a subsequent study, irrigation water containing E. coli O157:H7 at 10⁸ CFU/ml was sprayed onto either the abaxial (lower) or adaxial (upper) side of leaves of field-grown lettuce under sunny or shaded conditions. E. coli O157:H7 was detectable on the leaf surface 27 days postspraying, but survival was higher on leaves sprayed on the abaxial side than on leaves sprayed on the adaxial side. Internalization of E. coli O157:H7 into lettuce leaves also occurred with greater persistence in leaves sprayed on the abaxial side (up to 14 days) than in leaves sprayed on the adaxial side (2 days).

Document Type: Research article

Affiliations: 1: Center for Food Safety, Department of Food Science and Technology, 1109 Experiment Street, University of Georgia, Griffin, Georgia 30223, USA 2: Department of Horticulture, University of Georgia, Tifton, Georgia 31793, USA 3: National Institute of Microbial Forensics and Food & Agricultural Biosecurity, Oklahoma State University, Stillwater, Oklahoma 74078, USA

Publication date: 2010-06-01

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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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Surface and Internalized Escherichia coli O157:H7 on Field-Grown Spinach and Lettuce Treated with Spray-Contaminated Irrigation Water

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