Monoclonal antibody detection of IncF group plasmid-encoded TraT protein in clinical isolates of Escherichia coli

The TraT protein specified by IncF group plasmids mediates surface exclusion and bacterial resistance to the lethal activities of serum. In this study, an anti-TraT protein monoclonal antibody was generated which failed to react with TraT+ bacteria but which efficiently detected solubilized TraT protein in Western blots and in an enzyme-linked immunosorbent assay. Use of this antibody to screen clinical and nonclinical isolates of Escherichia coli for the production of TraT protein revealed its presence in a modest proportion (38%) of normal fecal strains, a significantly higher proportion of clinical strains (51 to 73%), and an even higher proportion (78 to 88%) of clinical strains concomitantly producing the K1 capsule, an important virulence factor of E. coli.