Effect of Route of Introduction and Host Cultivar on the Colonization, Internalization, and Movement of the Human Pathogen Escherichia coli O157:H7 in Spinach

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 oil 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 oil very few plants and in low numbers (10(2) to 10(6) CFU/g fresh tissue) that decreased over time. Stern puncture inoculations, simulating natural wounding, rarely resulted ill 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 oil cv. Space and were dispersed over an area of up to 0.3 mm(2). The highest bacterial numbers were observed oil cv. Tyee but were dispersed only up to 0.15 mm(2), suggesting that cv. Tyee may provide protected niches of 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 wits found for natural entry into the plant interior. The results are relevant for interventions aimed at minimizing produce contamination by human pathogens.