Association of Escherichia Coli 0157:H7 in Flocs: Role of Extracellular Polymeric Substances and Fate of Pathogenic Organisms

In North America, Escherichia coli (E. coli) O157:H7 has been frequently associated with outbreaks of food-borne and water-borne infection. The association of E. coli O157:H7 to flocs is hypothesized to be a potential mechanism of transport and survival in natural environments. This study examines this hypothesis with a focus on the role of extracellular polymeric substances (EPS) and on E. coli O157:H7 survival/pathogenicity in an aquatic environment. The floc characterization experiment indicted that EPS play a significant role in floc stability. The EPS distribution experiment revealed abundant hydrophobic protein throughout the floc, which contributed to floc stability and microbial adhesion. In examining the survivability of E. coli O157:H7 in a low nutrient water sample for 10-day incubation, more floc-adherent E. coli O157:H7 survived than the free-living form since EPS provided protection, nutrients and stable sites for survival. Surviving E. coli O157:H7 exhibited both decreased host adhesion ability and ª-actinin accumulation; however, their infection ability was not affected. This suggests that low nutrient levels did not affect pathogenicity over 10 days in this study.