CHARACTERIZATION OF THE ROLES OF HEMOLYSIN AND OTHER TOXINS IN ENTEROPATHY CAUSED BY ALPHA-HEMOLYTIC ESCHERICHIA-COLI LINKED TO HUMAN DIARRHEA

Escherichia coli strains producing alpha-hemolysin have been associate d with diarrhea in several studies, but it has not been clearly demons trated that these strains are enteropathogens or that alpha-hemolysin is an enteric virulence factor. Such strains are generally regarded as avirulent commensals. We examined a collection of diarrhea-associated hemolytic E. coli (DHEC) strains for virulence factors, No strain pro duced classic enterotoxins, but they all produce;I an alpha-hemolysin that was indistinguishable from that of uropathogenic E. coli strains. DHEC strains also produced other toxins including cytotoxic necrotizi ng factor 1 (CNF1) and novel toxins, including a cell-detaching cytoto xin and a toxin that causes HeLa cell elongation, DHEC strains mere en teropathogenic in the RITARD (reversible intestinal tie adult rabbit d iarrhea) model of diarrhea, causing characteristic enteropathies, incl uding inflammation, necrosis, and colonic cell hyperplasia in both sma ll and large intestines. Alpha-hemolysin appeared to be a major virule nce factor in this model since it conferred virulence to nonpathogenic E. coli strains. Other virulence factors also appear to be contributi ng to virulence. These Endings support the epidemiologic link to diarr hea and suggest that further research into the role of DHEC and alpha- hemolysin in enteric disease is warranted.