VIRULENCE PROPERTIES AND ATTACHING-EFFACING ACTIVITY OF ESCHERICHIA-COLI O45 FROM SWINE POSTWEANING DIARRHEA

Escherchia coli 045 isolates associated with swine postweaning diarrhea in Quebec were characterized with respect to virulence determinants genetically and investigated for their attaching and effacing (A/E) activities by experimental inoculation of gnotobiotic piglets and by the HEp-2 cell adherence assay. All of 32 isolates tested were negative for enterotoxigenic and verotoxigenic E. coli virulence determinants, heat-labile enterotoxin (LT), heat-stable enterotoxins (STap, STb), verotoxins (VT1, VT2), and F4 (K88), F5 (K99), F6 (987P), and F4l, except one STb-positive and two F4-positive isolates. A total of 25 isolates hybridized with an EaeA probe, and 11 hybridized with an enteropathogenic E. coli adherence factor (EAF) probe. None of 32 isolates hybridized with a bundle-forming pilus (BFP) probe. The EAF, EaeA, and BFP factors have been associated with human enteropathogenic E. coli strains. A total of 10 of 12 eaeA-positive porcine 045 isolates induced A/E lesions characterized by intimate adherence of bacteria to the intestinal epithelial cell membrane with effacement of the microvilli, similar to those of human attaching-effacing E. coli. However, A/E lesions were not observed in the piglets inoculated with any one of three eaeA-negative 045 isolates. All E. coli 045 isolates were non-adherent to WEp-2 cells. Thus, we have demonstrated the production of typical A/E lesions by nonenterotoxigenic E. coli 045 isolates from swine postweaning diarrhea. The results indicate the significance of the eaeA gene in A/E activities of these isolates and suggest that EAF and and BFP are not involved in 045 E. coli infection of weaning piglets.