Functional heterogeneity of intestinal Escherichia coli strains expressing type 1 somatic pili (fimbriae): assessment of bacterial adherence to intestinal membranes and surface hydrophobicity.

Although the role of host-specific, nonmannose-sensitive pilus adhesins in the intestinal adherence of pathogenic Escherichia coli is well established, a similar role for mannose-sensitive type 1 or common pili is less clear, since these structures can be expressed by most E. coli, even nonpathogens. We first examined whether type 1 pili, expressed by the rabbit-effacing, adherent, enteropathogenic E. coli strain RDEC-1, mediated interactions with intestinal membranes of several species and compared these interactions with those mediated by the nonmannose-sensitive adhesin of RDEC-1. We next grew a series of E. coli intestinal strains in static broth to promote type 1 pilus expression and determined whether E. coli expressing type 1 pili differed in their affinity for intestinal membranes (as measured by phase-contrast microscopy and aggregometry), hydrophobic surface properties, net negative surface charge (as measured by hydrophobic interaction chromatography and salt aggregation), and hemagglutination patterns. In contrast to the species-specific attachment to rabbit brush borders of RDEC-1 expressing its nonmannose-sensitive adhesin, type 1 pili on RDEC-1 mediated mannose-sensitive attachment to intestinal membranes of all four species tested. Expression of type 1 pili on other E. coli strains resulted in varying degrees of nonspecies-specific, mannose-sensitive attachment to intestinal membranes. This attachment correlated with increasing surface hydrophobicity rather than with hemagglutination patterns. These results indicate that various E. coli strains expressing type 1 pili are functionally heterogeneous and suggest that some type 1 pili might contribute to in vivo enteroadherence.