A flagellated motile Salmonella Gallinarum mutant (SG Fla+) elicits a pro-inflammatory response from avian epithelial cells and macrophages and is less virulent to chickens

Salmonella enterica subspecies enterica serovar Gallinarum biovar Gallinarum (SG) is a non-flagellated bacterium which causes fowl typhoid, a systemic disease associated with high mortality in birds. It has been suggested that the absence of flagella in SG is advantageous in the early stages of systemic infection through absence of TLR-5 activation. In order to investigate this hypothesis in more detail a flagellated and motile SG mutant (SG Fla+) was constructed. The presence of flagella increased invasiveness for chicken kidney cells (CKC) while its presence did not alter survival in HD11 macrophages. SG Fla+ induced higher levels of CXCLi2, IL-6 and iNOS mRNA expression in CKC than the SG parent strain. The expression of genes responsible for immune response mediators in infected HD11 macrophages were not related to the presence of flagella. Mortality rates were lower in birds challenged with SG Fla+ when compared with the SG parent. SG Fla+ was recovered from caecal contents which showed pathological changes suggestive of inflammation and suggested increased colonization ability.