Cytotoxic Effect in Human Colon of Enterohemorrhagic Escherichia coli Isolated from Calves with Bloody Diarrhea

PISTONE CREYDT V; VENZANO A; VILTE D; MERCADO E; IBARRA C

Melbourne, Australia

Congreso; 6th International Symposium on Shiga Toxin (Verocytotoxin) – producing Escherichia coli infections; 2006

Shiga toxin-producing E. coli (STEC) is the emergent pathogen of higher impact in foods, being its main reservoir bovine cattle. STEC can cause diarrhea, hemorrhagic colitis and hemolytic-uremic syndrome (HUS). Previous studies show that STEC pathogenic in humans also colonize the intestine of calves, and may produce diarrhea. The present work studies the cytotoxic action in human colon of strains of STEC isolated from calves with bloody diarrhea. These strains are genotipically and phenotypically characterized as E. coli O26:H11, stx2, eae-β, EHly and E. coli O111:H- stx1, eae-θ, EHly. Colon fragments proceeded from surgical operations performed on adult patients with cancer. Colonic mucosa was mounted as a diaphragm in a Ussing chamber and incubated for 1 h with 200  l of bacteria (OD600 = 0,5) added in the mucosal bath. Net water flow (Jw) measured across the mucosal barrier decreased (p < 0,01) and the short-circuit current (Isc) increased (p < 0,01) compared to E. coli DH5-alpha used as a negative control. Tissues from both experimental strains showed a histological damage that consisted in tissue fragments with erosion of the mucose, epithelial exfoliation, and presence of pseudo-membranes in the lumen, composed by necrotic epithelial cells, mucous, neutrophiles and bacillus. The histopathology was similar to that observed in isquemic colitis of both human and bovine intestine infected by STEC. The cell culture supernatant filtered from E. coli 026:H11 strain containing Stx2 among its bacterial products, also produced a decrease of Jw (p<0.05) without altering the electrical parameters. This inhibitory effect on Jw disappeared when the supernatants were previously incubated with specific antibodies against subunit B of Stx2. This is the first study showing that STEC strains isolated from bovine cattle produce cytotoxic effects in vitro in human colon.