The role of pO157 in Escherichia coli O157:H7 associated with colonization of cattle and persistence of various environments /by Ji Youn Lim.

Escherichia coli O157:H7 is a food-borne pathogen causing hemorrhagic colitis and the life threatening seqeulae, the hemolytic uremic syndrome in humans. Healthy cattle are the major reservoir of E. coli O157:H7 and carry this microorganism without symptoms. Decreasing carriage or eliminating E. coli O157:H7 in cattle will reduce the risk of human infection and effective intervention strategies require an understanding of the interactions between cattle and E. coli O157:H7 and bacterial survival on the farm. Most clinical E. coli O157:H7 isolates have an F-factor like 92-kb plasmid, pO157. We hypothesized that the genes on pO157 of E. coli O157:H7 are required for colonization of cattle and persistence in various environments. To test this hypothesis, we compared wild-type E. coli O157:H7 and isogenic pO157-cured mutants in vitro and in vivo . An isogenic pO157-cured mutant of E. coli O157:H7 ATCC 43894 (43894-Cu) showed enhanced resistance to acidic condition and passage through the bovine gastrointestinal tract, but did not colonize cattle as well as wild-type E. coli O157:H7 ATCC 43894 (43894). After the deletion of pO157, many proteins were differentially expressed including glutamate decarboxylase and tryptophanase which are associated with acid resistance and survival in salvage conditions. In addition, E. coli O157:H7 Sakai (Sakai) was investigated for the characterization of the role of pO157 in detail. Similar to 43894-Cu, an isogenic pO157-cured Sakai (Sakai-Cu) showed enhanced survival in acidic conditions and did not colonize cattle as well as wild-type Sakai. Unlike, 43894-Cu, Sakai-Cu had antibiotic susceptibility changes compared to Sakai. Phenotypic diversity among Sakai, 43894, Sakai-Cu, and 43894-Cu were analyzed for 1,920 conditions using phenotypic microarray technology. An unexpected influence of essentially identical pO157 on a wide array of growth/survival conditions differed between Sakai and 43894. The role of plasmid O157 in biofilm formation was also investigated. Compared to wild- type Sakai, the biofilm formed by Sakai-Cu produced less extracellular carbohydrates, had lower viscosity, and did not give rise to colony morphology variants that hyper-adhered to solid surfaces. This was the first demonstration that pO157 affect E. coli 0157:H7 biofilm formation and implies a role for the pO157 in bacterial survival and persistence. In conclusion, the pO157 is required for the colonization of cattle and is associated with survival and persistence in various-environments.Thesis (Ph. D., Microbiology, Molecular Biology and Biochemistry)--University of Idaho, August 2009