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

Providencia alcalifaciensis a member of the Enterobacteriaceae family that occasionally causes diarrheagenic illness in humans via the intake of contaminated foods. Despite the epidemiological importance ofP. alcalifaciens, little is known about its pathobiology. Here we report thatP. alcalifacienscauses barrier dysfunction in Caco-2 cell monolayers and induces apoptosis in calf pulmonary artery endothelial cells.P. alcalifaciensinfection caused a 30% reduction in transepithelial resistance in Caco-2 cell monolayers, which was greater than that for cells infected withShigella flexnerior non-pathogenicEscherichia 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 theP. 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 thatP. alcalifaciensLPSs reduced occludin levels, whereas LPSs fromShigellaorE. colidid not. Although the viability of Caco-2 cells was not altered significantly, the calf pulmonary artery endothelial cell line was highly sensitive toP. alcalifaciensinfection. This sensitivity was indeed dependent on LPS, which induced rapid apoptosis. Together, these data show thatP. alcalifaciensLPSs participate in epithelial barrier dysfunction and endothelial apoptosis. The findings give insight into the LPS-dependent cell signal events affecting diarrheagenicity during infection withP. alcalifaciens. [ABSTRACT FROM PUBLISHER]