The Gene , Harbored by the Subtilase-Encoding Pathogenicity Island, Is Involved in the Ability of Locus of Enterocyte Effacement-Negative Shiga Toxin-Producing Escherichia coli Strains To Invade Monolayers of Epithelial Cells.

Locus of enterocyte effacement (LEE)-negative Shiga toxin (Stx)-producing (STEC) strains are human pathogens that lack the LEE locus, a pathogenicity island (PAI) involved in the intimate adhesion of LEE-positive strains to the host gut epithelium. The mechanism used by LEE-negative STEC strains to colonize the host intestinal mucosa is still not clear. The cell invasion determinant , previously described in enterotoxigenic strains, has been identified in LEE-negative STEC strains that possess the subtilase-encoding pathogenicity island (SE-PAI). We evaluated the role of the gene , present in these LEE-negative STEC strains, in the invasion of monolayers of cultured cells. We observed that these strains were able to invade Caco-2 and HEp-2 cell monolayers and compared their invasion ability with that of a mutant strain in which the gene had been inactivated. Mutation of the gene resulted in a strong reduction of the invasive phenotype, and complementation of the mutation with a functional copy of the gene restored the invasion activity. Moreover, we show that the gene is overexpressed in bacteria actively invading cell monolayers, demonstrating that is involved in the ability to invade cultured monolayers of epithelial cells shown by SE-PAI-positive , including STEC, strains. However, the expression of the gene in the K-12 strain JM109 was not sufficient, in its own right, to confer to this strain the ability to invade cell monolayers, suggesting that at least another factor must be involved in the invasion ability displayed by the SE-PAI-positive strains.