Authors: Mitra, R.¹; Cuesta-Alonso, E.²; Wayadande, A.¹; Talley, J.¹; Gilliland, S.²; Fletcher, J.¹

Source: Journal of Food Protection®, Volume 72, Number 7, July 2009 , pp. 1521-1530(10)

Publisher: International Association for Food Protection

Abstract:

Human pathogens can contaminate leafy produce in the field by various routes. We hypothesized that interactions between Escherichia coli O157:H7 and spinach are influenced by the route of introduction and the leaf microenvironment. E. coli O157:H7 labeled with green fluorescent protein was dropped onto spinach leaf surfaces, simulating bacteria-laden raindrops or sprinkler irrigation, and survived on the phylloplane for at least 14 days, with increasing titers and areas of colonization over time. The same strains placed into the rhizosphere by soil infiltration remained detectable on very few plants and in low numbers (10² to 10⁶ CFU/g fresh tissue) that decreased over time. Stem puncture inoculations, simulating natural wounding, rarely resulted in colonization or multiplication. Bacteria forced into the leaf interior survived for at least 14 days in intercellular spaces but did not translocate or multiply. Three spinach cultivars with different leaf surface morphologies were compared for colonization by E. coli O157:H7 introduced by leaf drop or soil drench. After 2 weeks, cv. Bordeaux hosted very few bacteria. More bacteria were seen on cv. Space and were dispersed over an area of up to 0.3 mm². The highest bacterial numbers were observed on cv. Tyee but were dispersed only up to 0.15 mm², suggesting that cv. Tyee may provide protected niches or more nutrients or may promote stronger bacterial adherence. These findings suggest that the spinach phylloplane is a supportive niche for E. coli O157:H7, but no conclusive evidence was found for natural entry into the plant interior. The results are relevant for interventions aimed at minimizing produce contamination by human pathogens.

Document Type: Research article

Affiliations: 1: Department of Entomology and Plant Pathology, Robert E. Kerr Food and Agricultural Products Center, Oklahoma State University, Stillwater, Oklahoma 74078, USA 2: Department of Animal Science, Robert E. Kerr Food and Agricultural Products Center, Oklahoma State University, Stillwater, Oklahoma 74078, USA

Publication date: 2009-07-01

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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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