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Measurements of fitness and intra-specific competition between commensal Escherichia coli and E. coli O157:H7 strains

Lisa Marie Durso, University of Nebraska - Lincoln

Abstract

E. coli O157:H7 is an important foodborne pathogen that can cause bloody diarrhea, hemolytic uremic syndrome, and sometimes even death. The main vehicle for this pathogen is thought to be foods of cattle origin. However, despite intense research efforts aimed at controlling and eliminating E. coli O157:H7, little is known about the means by which this organism spreads and persists in foods and the food production environment, including its tenure in the cattle host, and its survival outside of humans and cattle. It is also not understood what physiological properties, if any, distinguish these pathogens from their harmless commensal counterparts that live as normal members of the human and bovine gastrointestinal tracts. These are the questions addressed in this research. ^ Individual and competitive growth rate experiments were conducted in four environments representing the human gastroinstestinal tract, the cattle rumen, the environment outside of the human and cattle hosts, and an ideal growth environment. These experiments revealed no difference either between commensal E. coli and E. coli O157:H7 strains, or between E. coli O157:H7 subgroups of cattle versus human strains, or OBGS lineage one versus lineage two strains. Some differences were observed, however, in carbon source utilization patterns, intra-specific competition strategies, and antibiotic resistance patterns. A subset of 20 carbon sources was identified that was differentially oxidized by commensal E. coli strains, compared to E. coli O157:H7 strains, while seven substrates were differentially oxidized by OBGS lineage one versus lineage two strains, and cattle O157:H7 versus human O15:H7 E. coli strains. Some of these phenotypic differences were shown to be attributable to genotypic differences in the genetic sequences of the strains, and the phenotypic differences were sufficient to roughly distinguish commensal E. coli from E. coli O157:H7 strains phylogentically. Intra-specific competition strategies were markedly different for commensal E. coli compared to E. coli O157:H7 strains, with the E. coli O15:H7 strains more frequently producing inhibitory substances under conditions tested, although both groups displayed moderate sensitivity. Differences, though minor, were also noted in the antibiotic resistance patterns of the commensal E. coli strains compared to the E. coli O157:H7 strains. ^

Subject Area

Biology, Ecology|Agriculture, Food Science and Technology|Biology, Microbiology

Recommended Citation

Durso, Lisa Marie, "Measurements of fitness and intra-specific competition between commensal Escherichia coli and E. coli O157:H7 strains" (2003). ETD collection for University of Nebraska - Lincoln. AAI3078607.
http://digitalcommons.unl.edu/dissertations/AAI3078607

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