Genomic Analysis of Escherichia coli O157:H7 Populations from Cattle and Humans (1998-02726)

Genetic fingerprinting of E. coli 0157:H7 strains from cattle herds indicates that certain strains can be repeatedly isolated from agiven herd over time (persistent population) despite the fact that other genetically distinct E. coli 0157:H7 strains may be introduced into the herd but are unable to displace the persistent population. These results suggest that persistent strains are better able to survive and/or propagate in these environments. Are there particular herd management practices that have been selected for these persistent populations, and are these strains genetically distinct from those isolated from infected humans?
<P>We have developed a powerful technique, termed high-resolution genotyping (HRGT), that permits identification of even minor genetic differences between different E. coli 0157:H7 strains. This procedure will be used to develop a database for rigorous assessment of the genetic relatedness of persistent and non-persistent isolates. Non-persistent isolates will be examined in further detail (full genome coverage) by HRGT to identify genetic differences that may be related to persistence. The genes that are marked by these differences will then be examined to begin assessing how their function may contribute to persistence and whether particular herd management practices may have played a role in selecting for alterations in these genes. Ultimately these results may provide a rational basis for understanding the impact of herd management practices on the population structure of this organism.