Evaluation of Treatments for Elimination of Foodborne Pathogens on the Surface of Leaves and Roots of Lettuce (Lactuca sativa L.)

Authors: Zhang, Guodong; Ma, Li; Beuchat, Larry R.; Erickson, Marilyn C.; Phelan, Vanessa H.; Doyle, Michael P.

Source: Journal of Food Protection®, Volume 72, Number 2, February 2009 , pp. 228-234(7)

Publisher: International Association for Food Protection

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Abstract:

Several outbreaks of Salmonella and Escherichia coli O157:H7 infections have been associated with consumption of leafy greens. Questions remain concerning the ability of these pathogens to become internalized within lettuce and spinach tissues. An effective validated surface disinfection method for lettuce is needed before factors affecting internalization of pathogens can be studied. The objective of this study was to develop a surface disinfection method for lettuce leaves and roots. Iceberg lettuce (Lactuca sativa L.) leaves cut into pieces (3 by 3 cm) and lettuce roots were inoculated by immersing in suspensions of five-strain mixtures of green fluorescent protein-labeled E. coli O157:H7, Salmonella, or Listeria monocytogenes at populations of 7 to 8 log CFU/ml for 10 min at 20 ± 1°C. Inoculated samples were placed in a laminar flow biosafety cabinet for 30 min before treating with disinfectants. Thirteen surface disinfection methods were compared for their efficacy in killing E. coli O157:H7 on lettuce leaf and root surfaces. E. coli O157:H7 initially at 5.8 or 6.8 log CFU/leaf piece or root was not detected by enumeration (<0.6 log CFU per leaf piece) on samples treated for 20 min with 10,000 μg/ml sodium hypochlorite (NaHClO) or in solutions containing ethanol and mercuric chloride (HgCl₂). With all other methods, E. coli O157:H7 populations ranged from 2.8 to 4.4 CFU per leaf piece or root after treatment. Trends in leaf and root print and enrichment culture results were consistent with enumeration results. Dipping in 80% ethanol for 10 s followed by immersion in 0.1% HgCl₂ for 10 min was determined to be the most effective surface disinfection method for inactivating E. coli O157:H7 on lettuce leaves and roots and was also validated for inactivating Salmonella and L. monocytogenes.

Document Type: Research article

Affiliations: 1: Center for Food Safety, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA

Publication date: 2009-02-01

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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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Evaluation of Treatments for Elimination of Foodborne Pathogens on the Surface of Leaves and Roots of Lettuce (Lactuca sativa L.)

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