Decreased colonization of chicks by Salmonella enterica serovar Gallinarum expressing mannose-sensitive FimH adhesin from Salmonella enterica serovar Enteritidis

To investigate the role of non-hemagglutinating type 1 fimbriae in the pathogenesis of Salmonella Gallinarum, the isogenic mutant elaborating type 1 fimbriae with mannose-sensitive (MS) variant of the FimH adhesin from Salmonella Enteritidis and the mutant strain with no FimH expression were constructed. Their binding to chicken leukocytes in vitro and invasiveness in 1-day-old chicks were studied. Our results demonstrated that S. Gallinarum type 1 fimbriae with an endogenous variant of the FimH adhesin mediated mannose-resistant (MR) binding to avian leukocytes and did not bind to human epithelial cells. However, after allelic replacement of the FimH, mutated fimbriae with S. Enteritidis variant of the FimH adhesin bound to both cell types in a mannose-dependent manner. In chick model, S. Gallinarum expressing wild-type FimH variant colonized cecal tonsils and bursa of Fabricius more effectively and invaded the spleen and liver in greater numbers than S. Gallinarum fimH knockout strain or mutant expressing MS FimH variant from S. Enteritidis. The invasive potential of the latter was greatly reduced in chicks since no viable bacteria expressing MS variant of the adhesin could be recovered from intestinal lymphoid tissues or liver over a 6 days course of infection. Together, these results demonstrate that the S. Gallinarum type 1 fimbriae with the endogenous MR variant of the FimH protein increase systemic dissemination of S. Gallinarum and colonization of internal organs in chicks indicating the importance of these adhesive structures in the virulence of S. Gallinarum.