Contribution of the csgA and bcsA genes to Salmonella enterica serovar Pullorum biofilm formation and virulence

Salmonella biofilm formation is important to environmental stress resistance and virulence. However, the roles of the csgA and bcsA genes, which affect curli protein and cellulose production, respectively, in Salmonella enterica serovar Pullorum, are unknown. Here we constructed deletions in the csgA and bcsA genes in S. enterica serovar Pullorum strain S6702 and evaluated several aspects of biofilm formation and virulence. Delta csgA showed decreased production of curli fimbriae, while Delta bcsA had reduced cellulose production. Both mutants had a reduced ability to form biofilms. Delta csgA was reduced in adhesion and invasion to HeLa cells and exhibited decreased intracellular proliferation in HD11 macrophages. Delta bcsA exhibited increased proliferation in HD11 cells and replicated better in chicken spleens, as compared to the wild-type strain. Delta csgA virulence was attenuated in assays involving oral challenge of one-day-old chickens.