Characterization of Escherichia coli isolated from the tonsils of cattle.

During our studies on tonsillar colonization by Pasteurella haemolytica, we consistently found Escherichia coli to be one of the most prominent and prevalent bacterial species in the tonsils of healthy cattle. Since tonsillar isolates have not been characterized, we grouped 124 isolates from 87 healthy cattle from eight sources by hemolytic zone size and by carbon source utilization and probed them for selected virulence genes. They formed 3 groups by hemolytic zone size and 18 groups (of 2 to 31 isolates) by their metabolic patterns. Most groups included isolates from more than one source. Two isolates contained the Shiga-like toxin gene, and nine others contained the F41 accessory gene.