Providencia alcalifaciens causes barrier dysfunction and apoptosis in tissue cell culture: potent role of lipopolysaccharides on diarrheagenicity.

Providencia alcalifaciens is a member of the Enterobacteriaceae family that occasionally causes diarrheagenic illness in humans via the intake of contaminated foods. Despite the epidemiological importance of P. alcalifaciens, little is known about its pathobiology. Here we report that P. alcalifaciens causes barrier dysfunction in Caco-2 cell monolayers and induces apoptosis in calf pulmonary artery endothelial cells. P. alcalifaciens infection caused a 30% reduction in transepithelial resistance in Caco-2 cell monolayers, which was greater than that for cells infected with Shigella flexneri or non-pathogenic Escherichia coli. As with viable bacteria, bacterial lysates treated with heat, benzonase or proteinase, but not with polymixin B, were also involved in the cellular response. TLR4 antibody neutralisation significantly restored the P. alcalifaciens-induced transepithelial resistance reduction in Caco-2 cells, suggesting that lipopolysaccharides (LPSs) might play a central role in this cellular response. Western blotting further indicated that P. alcalifaciens LPSs reduced occludin levels, whereas LPSs from Shigella or E. coli did not. Although the viability of Caco-2 cells was not altered significantly, the calf pulmonary artery endothelial cell line was highly sensitive to P. alcalifaciens infection. This sensitivity was indeed dependent on LPS, which induced rapid apoptosis. Together, these data show that P. alcalifaciens LPSs participate in epithelial barrier dysfunction and endothelial apoptosis. The findings give insight into the LPS-dependent cell signal events affecting diarrheagenicity during infection with P. alcalifaciens.