Identification of plasmid-encoded mannose-resistant hemagglutinin and HEp-2 and HeLa cell adherence factors of two diarrheagenic Escherichia coli strains belonging to an enteropathogenic serogroup

Abstract

Two Escherichia coli strains (B/M 369 and C-35) belonging to enteropathogenic serogroup O86 were isolated from patients with infantile diarrhea and studied with respect to their cellular adherence properties. Both strains exhibited adherence (Ad+) to HEp-2 and HeLa cell monolayers in vitro and expressed mannose-resistant hemagglutinating (MRHA+) activity towards human, chicken, and sheep (but not mouse, rabbit, or guinea pig) erythrocytes. Cellular adherence properties of both strains could be substantially reduced by pronase treatment and by heat treatment (100°C for 5 min) of bacteria. Electron microscopic examination failed to reveal fimbria- or pilus-like structures on the bacterial cell surface. Conjugation experiments conducted with these strains suggested that both MRHA and HEp-2 and HeLa cell adherence factors were encoded by the same plasmid, with a size of 55 to 57 megadaltons (MDa). Further biochemical studies indicated that the cellular adherence factors were associated with cell surface structures of bacteria that were proteinaceous in nature. An antiserum, rendered specific for the 57-MDa plasmid (pRP201) products of B/M 369 by adsorption, reacted with both MRHA+ Ad+ strains, B/M 369 and C-35, but not with their 57- or 55-MDa plasmidless MRHA- Ad- transconjugants or with other MRHA- Ad- E. coli strains. Immunological studies showed that the absorbed antiserum recognized two proteins with subunit molecular sizes of 18 and 14.5 kDa that were present on the cell surfaces of both strains. Furthermore, the absorbed antiserum at subagglutinating dilutions did inhibit, although only partially, the MRHA and HEp-2 and HeLa cell adherence activities of both E. coli strains. All these results would indicate that some of the E. coli strains belonging to enteropathogenic serogroups express their adherence potential through factors that were hitherto unrecognized.