The effect of O-antigen length determinant wzz on the immunogenicity of Salmonella Typhimurium for Escherichia coli O2 O-polysaccharides delivery.

Attenuated Salmonella Typhimurium is a promising antigen delivery system for live vaccines such as polysaccharides. The length of polysaccharides is a well-known key factor in modulating the immune response induced by glycoconjugates. However, the relationship between the length of Lipopolysaccharide (LPS) O-antigen (OAg) and the immunogenicity of S. Typhimurium remains unclear. In this study, we assessed the effect of OAg length determined by wzz ST on Salmonella colonization, cell membrane permeability, antimicrobial activity, and immunogenicity by comparing the S. Typhimurium wild-type ATCC14028 strain to those with various OAg lengths of the Δwzz ST mutant and Δwzz ST ::wzz ECO2 . The analysis of the OAg length distribution revealed that, except for the very long OAg, the short OAg length of 2-7 repeat units (RUs) was obtained from the Δwzz ST mutant, the intermediate OAg length of 13-21 RUs was gained from Δwzz ST ::wzz ECO2 , and the long OAg length of over 20 RUs was gained from the wild-type. In addition, we found that the OAg length affected Salmonella colonization, cell permeability, and antibiotic resistance. Immunization of mice revealed that shortening the OAg length by altering wzz ST had an effect on serum bactericidal ability, complement deposition, and humoral immune response. S. Typhimurium mutant strain Δwzz ST ::wzz ECO2 possessed good immunogenicity and was the optimum option for delivering E. coli O2 O-polysaccharides. Furthermore, the attenuated strain ATCC14028 ΔasdΔcrpΔcyaΔrfbPΔwzz ST ::wzz ECO2 -delivered E. coli O2 OAg gene cluster outperforms the ATCC14028 ΔasdΔcrpΔcyaΔrfbP in terms of IgG eliciting, cytokine expression, and immune protection in chickens. This study sheds light on the role of OAg length in Salmonella characteristics, which may have a potential application in optimizing the efficacy of delivered polysaccharide vaccines.