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To genotypically and phenotypically characterize 1100 E. coli isolates from cattle in order to understand how resistance to antibiotics is disseminated.
Approach: 1. PCR-based replicon typing (PBRT) of E. coli isolates to determine plasmid (replicon) types carried by the isolates. This will also include PCR to determine the type of beta-lactamase gene(s) that may be carried by the isolates. Initially detection of blacmy-2 will be examined since it has been highly prevalent among bacteria isolated from cattle. 2. Demonstrate that transmissibility of the resistant phenotype to recipient E. coli and Salmonella in vitro, evaluate the rate of plasmid transfer to recipient E. coli with and without the presence of ceftiofur, and that transmissibility occurs via a mobile/mobilizable plasmid. 3. Molecularly characterize the isolates using pulsed-field electrophoresis (PFGE) to determine if resistance occurs in a single (or a limited number of) clones or in a broad array of genotypes. 4. Molecular characterization of the resistance-encoding plasmid to identify plasmids shared among different strains.