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The experiments outlined in this proposal are therefore designed to use genomics and bioinformatics to identify the DNA sequence of all chromosome alterations that distinguish the two subpopulations. These sequences will provide two very critical tools to promote our understanding of the potential for these subpopulations for virulence in humans.
The presence of E. coli O157: H7 in cattle and the subsequent potential for transmission to humans through contaminated beef poses a significant problem to the food production industry, regulatory officials, and consumers alike. Recent studies using high resolution methods for chromosome comparison have demonstrated the existence of two genetically distinct subpopulations of this organism that have apparently unique ecological niches. Since one of the subpopulations was underrepresented among human clinical isolates that were tested, the hypothesis arose that this subpopulation is either less virulent or is inefficiently transmitted to humans through contaminated beef. In order to test this hypothesis, tools need to be developed to facilitate precise measurement of the distribution of these subpopulations and to enhance our understanding of the genetic basis for their unique ecologies. First, a polymerase chain reaction-based method will be devised that can rapidly categorize E. coli O157: H7 isolates into the two different subpopulations. This method will facilitate large-scale epidemiological studies on transmission patterns of the subpopulations in animal and human environments. Secondly, understanding the nature of the chromosome alterations will provide a means for genetically dissecting the consequences of the alterations on the physiology and ecology of the subpopulations and allow us to begin making connections between selective and suppressive forces that are at work in different animal production environments.