Human neutrophils and their products induce shiga toxin production by enterohemorrhagic Escherichia coli

The Shiga toxins (Stx) are critical virulence factors for Escherichia coli O157:H7 and other serotypes of enterohemorrhagic E. coli (EHEC). These pote nt toxins are encoded in the genomes of temperate lambdoid bacteriophages. We recently demonstrated that induction of the resident Stx2-encoding proph age in an O157:H7 clinical isolate is required for toxin production by this strain. Since several factors produced by human cells, including hydrogen peroxide (H2O2), are capable of inducing lambdoid prophages, we hypothesize d that such molecules might also induce toxin production by EHEC. Here, we studied whether H2O2 and also human neutrophils, an important endogenous so urce of H2O2, induced Stx2 expression by an EHEC clinical isolate. Both H2O 2 and neutrophils were found to augment Stx2 production, raising the possib ility that these agents may lead to prophage induction in vivo and thereby contribute to EHEC pathogenesis.