Escherichia coli O157:H7 outbreaks linked to tainted fresh produce have increased during recent years. The aim of this study is to... Show moreEscherichia coli O157:H7 outbreaks linked to tainted fresh produce have increased during recent years. The aim of this study is to characterize the cell surface properties, chlorine resistance and attachment to leafy greens of several E. coli O157:H7 strains belonging to different phylogenetic clades, in order to reveal if there is any correlation between their survival and bacterial cell surface properties. Six strains chosen among the nine E. coli O157:H7 clades included the fresh produce outbreak associated strains Sakai (1996 sprout outbreak in Japan) and TW14359 (2006 spinach outbreak in the US). The growth kinetics of these strains was compared in BHI broth containing 0.81 ppm free chlorine. Cell surface hydrophobicity, auto-aggregation and curli production were determined by in vitro assays and compared to the generic E. coli strain BW25113. The results showed that these E. coli O157:H7 strains exhibited different chlorine resistances regardless of their phylogenetic distance. They were approximately 20% more hydrophilic (p=0.0072) and showed 77% less auto-aggregated cells (p=0.049) after overnight incubation in broth than the generic E. coli strain. However, no distinguishable hydrophobic or aggregation properties were observed among the six E. coli O157:H7 strains despite their different resistances toward chlorine treatment. Curli production measured by a Congo-Red binding assay in suspension varied among the strains and exhibited no correlation with chlorine resistance. In preliminary studies of chlorine exposure (0.81 ppm) of cells being attached to spinach leaf surface, the spinach outbreak strain TW14359 showed less inactivation (2.6-fold) than the sprout outbreak strain Sakai (15-fold). The information generated from this study will help to develop more effective interventions used in the produce industry. M.S. in Food Safety and Technology, December 2011 Show less