Elimination of Salmonella enterica serotype Enteritidis in intestinal epithelial cells by mechanisms other than nitric oxide

Production of nitric oxide (NO) by intestinal epithelial cells is induced after infection with Salmonella spp. or some other enteroinvasive bacteria. However, direct evidence of the role of NO in the elimination of intracellular pathogens in intestinal mucosa has not been established. This study investigated whether NO mediates killing of Salmonella enterica serovar Enteritidis in human intestinal epithelial cells by using parent Henle-407 cell line and a transfected cell line not capable of induced NO production (Henle-NO(def)). NO synthesis was studied as combined accumulation of nitrite and nitrate, as inducible nitric oxide synthase (iNOS) protein determined by Western blotting and as iNOS mRNA detected by reverse transcription (RT)-PCR. Although parent and Henle-NO(def) cells differed markedly in their ability to produce NO after infection, they eliminated S. Enteritidis equally, as determined by cfu counts. The presence of aminoguanidine, a selective iNOS inhibitor, during the infection blocked the production of NO but did not affect the elimination of the bacteria. These data suggest that NO does not have a direct role in the elimination of intracellular Salmonellae by human intestinal epithelial cells.