Cytotoxic effect in human colon of enterohemorrhagic Escherichia coli isolated from calves with bloody diarrhea.

PISTONE CREYDT V, VENZANO A, VILTE DA, ELSA C. MERCADO E, IBARRA C.

Melbourne, Australia

Congreso; VTEC2006 International Symposium and Workshop on Shiga toxin (verocytotoxin)-producing Escherichia coli infections.; 2006

Australian Society for Microbiology

Enterohemorrhagic E. coli (EHEC) is a major threat to public health in Argentina. Previous studies have demonstrated that argentinean cattle are an important reservoir of virulent EHEC serotypes. The aim of this research was to study the cytotoxic action in human colon of two EHEC strains isolated from calves with bloody diarrhea. The E. coli 97/23A and 01/289-1 strains were characterized as E. coli O26:H11, stx2, eae-ß, ehxA, and E. coli O111:HNM, stx1, eae-θ, ehxA, respectively. Colon fragments proceeded from operations performed on adult patients with cancer. Sections of macroscopically unaffected regions were conveniently mounted as a diaphragm in an Ussing chamber and incubated for 1 h with 200 μl of a culture of LB bacteria culture (OD600 = 0.5) added in the mucosal bath. Results indicate that both, E. coli 97/23A and 01/289-1 strains produced a decrease(p < 0.01) of net water flux (Jw) and an increase (p < 0.01) of short-circuit current across the mucosal barrier. E. coli DH5-α culture was used as negative control. The E. coli 97/23A filtered culture supernatant produced a decrease on Jw (p<0.05) without altering the electrical parameters. This inhibitory effect on Jw disappeared when the supernatant was previously incubated with specific antibodies against Shiga toxin 2B subunit. Both experimental strains induced histopathological damage consisting in erosion of the mucosa and epithelial exfoliation, with formation of pseudomembranes constituited by necrotic epithelial cells, mucous, neutrophiles and bacteria. Similar histopathological lesions have been observed in EHEC-associated hemorrhagic colitis in humans and natural and experimental infections of calves with bovine EHEC. These experiments demonstrate that non-O157 EHEC strains isolated from diarrheic calves are able to produce cytotoxic effects with alterations of physiological parameters in human colon in vitro, and reinforce the role of bovine as major source of EHEC to humans.