VIRULENCE OF AN ESCHERICHIA-COLI O157-H7 SORBITOL-POSITIVE MUTANT

Virulence and pathogenicity of an Escherichia coli 0157:H7 sorbitol-po sitive mutant were investigated with an infant rabbit animal model as well as a battery of in vitro assays. Total cell lysate protein profil es, outer membrane protein profiles, plasmid profiles, and levels of c ytotoxic activity against Vero cells were similar in the wild-type and mutant strains. Both adhered to intestinal epithelial cells in cultur e and reacted with fluorescein isothiocyanate-labeled antiserum agains t E. coli 0157:H7. The mutant appeared to be similar to the wild type in all respects except in its ability to ferment sorbitol. [C-14]sorbi tol uptake and sorbitol-6-phosphate dehydrogenase activities were nota bly increased in the mutant strain. Diarrhea developed in rabbits admi nistered the wild-type strain and in those fed the sorbitol-positive m utant. There was greater bacterial attachment and mucosal damage in th e cecum and large intestine than in the small intestine. Scanning elec tron microscopy revealed bacteria adhering as single cells and as aggr egates closely associated with mucus. Mucosal lesions consisted of are as of tissue necrosis with sloughing of epithelial cells. By transmiss ion electron microscopy, electron-dense necrotic epithelial cells were visible in areas where bacteria were present, and epithelial cell deb ris containing bacteria was observed between the villar luminal surfac es. Light microscopy of epithelial cells of intestinal sections of inf ected rabbits revealed noticeable vacuolation and spherical, pyknotic nuclei. These data indicate that the sorbitol-negative phenotype is no t associated with the pathogenicity of E. coli 0157:H7.