Effects of EHEC isolated from diarrheic calves in human colon in vitro.

PISTONE CREYDT V, TIRONI FARINATI C, VENZANO A, VILTE D, MERCADO E, IBARRA C.

Brasilia, Brasil

Congreso; 24 Congresso Brasileiro de Microbiologia.; 2007

Enterohemorrhagic Escherichia coli (EHEC) is one of the most important emergent food pathogen causing diarrhea, hemorrhagic colitis and hemolytic uremic syndrome in children. Although cattle are considered the principal source of human infections, the effects of EHEC strains from bovine origin in human colon have not been explored. In this work, we examined the physiological and morphological effects of strains 97/23-A (O26:H11; stx2; eae-β; ehxA) isolated from feces of calf with bloody diarrhea, on human colonic mucosa by the Ussing chamber technique. We have previously found that the absorptive net water flux (Jw) decreased while the short-circuit current (Isc) increased after the addition of bacterial culture. Also, tissues showed erosion of the mucosa with epithelial exfoliation and presence of pseudomembranes in the lumen. Colonic crypts were not disrupted. The ultrastructural evaluation showed microvilli changes and an atrophic mucosa. Treatment of the mucosa with culture supernatant from E. coli 97/23-A inhibited the absortive Jw although it was significantly lower than that observed using the whole culture. Isc remained unchanged. These effects were totally neutralized by preincubation with an antibody anti-Stx2B indicating that the functional alterations were due to Stx2 present in the culture supernatant. The addition of washed bacteria produced a similar Isc increase but a minor Jw decrease compared with the values observed using the whole cultures indicating that washed bacteria were capable to modify both Jw and Isc by themselves. This study shows that an EHEC strain isolated from calves with bloody diarrhea is able to produce both functional alterations and structural lesions in human colon due to Stx2 and bacterial cells. The evidence presented accentuates the epidemiological role of cattle as a source of EHEC human infections.