SHIGA TOXIN MODE OF ACTION IN E. COLI O157:H7 DISEASE

Tom G. Obrig

Department of Microbiology and Immunology, University of Rochester, Box 672, 601 Elmwood Avenue, Rochester, NY 14642

Received 12/2/97 Accepted 12/8/97

4. STX ISOTYPES PRODUCED BY E. COLI O157:H7

E. coli strains isolated from HUS patients produce moderate to high levels of Stxs (20). Such E. coli O157:H7 isolates normally produce either Stx2 alone or the combination of Stx1 and Stx2. Rarely do these strains produce Stx1 alone. Stx-producing E. coli serotypes other than O157:H7 have been associated with human disease, particularly outside the US, but toxin production by these isolates does not fit the pattern for O157:H7. A significant number of these non-O157:H7 isolates produce Stx1 alone, thus resembling Shigella dysenteriae 1 that elaborates Shiga toxin only (21). Whether either one of these toxin isotypes is more efficient in causing vascular damage in the clinical setting not known. However, Stx2 was shown to be approximately 1,000-times more potent than Stx1 in mice (22). Stx2 was also more potent, by three orders of magnitude, as a cytotoxic agent than Stx1 when incubated with human renal microvascular endothelial cells (23,24). These cells are the putative target of Stx in the hemolytic uremic syndrome caused by Stx-producing E. coli (25).