Metabolism of phenylpropionic acid in enteropathogenic Escherichia coli belonging to serogroup O111 and its application for diagnosis.

We evaluated a biochemical assay based on the ability to metabolise beta-phenylpropionic acid (PPA) as a diagnostic aid in the identification of typical enteropathogenic Escherichia coli (EPEC) strains. A total of 1061 E. coli strains of serogroups O55, O111, and O119 were initially characterised regarding their H types (serotypes) and the presence of EPEC DNA sequences, eae, EAF, and bfpA. In case of the serogroup O111 strains, 84.6% carried the typical EPEC markers, and the great majority of those (98.1%) were PPA-positive. In contrast, only 0.9% of the serogroups O55 and O119 strains carrying the typical EPEC markers (53.6% and 75.4%, respectively) were PPA-positive. We conclude that the PPA test is a useful method to detect typical EPEC strains only among strains of the O111 serogroup.