The Escherichia coli efflux pump TolC promotes aggregation of enteroaggregative E-coli 042

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen in both developing and industrialized countries. EAEC is defined as a diarrheal pathogen based on its characteristic aggregative adherence to HEp-2 cells in culture and its biofilm formation on the intestinal mucosa. We have reported that the novel protein AatA, which is encoded on the EAEC virulence plasmid pAA2, localizes to the outer membrane and facilitates export of the dispersin Aap across the outer membrane. Because AatA is an E. coli efflux pump TolC homolog, we investigated the role of TolC in the virulence of EAEC. No difference in Aap secretion was observed between the wild type and its tolC mutant (042tolC). However, characteristic aggregation in high-glucose Dulbecco's minimal essential medium for the wild type was diminished for 042tolC. In a microtiter plate assay, there were significantly more planktonic cells for 042tolC than for the wild type, while there were significantly fewer spontaneously precipitated cells on the substratum for 042tolC than for the wild type. In a HEp-2 cell adherence test, 042tolC showed less aggregative adherence than did the wild type. The strong aggregation and aggregative adherence were restored in the complement strain with tolC. In a transwell assay, planktonic cells of 042tolC decreased when cocultured with the wild type or the complement, while precipitated cells of 042tolC increased when cocultured with them. These results suggest that TolC promotes the aggregation and adhesion of EAEC 042 by secreting an assumed humoral factor.