Salmonella enterica serovar Enteritidis O-antigen polysaccharide (None commonly used; sometimes referred to as O-Ag or O-antigen, but these are generic terms)

Salmonella enterica serovar Enteritidis O-antigen polysaccharide is a highly variable, surface-exposed carbohydrate polymer that constitutes the O-antigen portion of the lipopolysaccharide (LPS) layer found on the outer membrane of Gram-negative bacteria. Structurally, it is a repeating oligosaccharide chain with a specific serovar-defining composition: in Enteritidis, the backbone consists of mannose, rhamnose, and galactose, plus a distinctive tyvelose sugar that confers serovar specificity (O:9 antigen). Genetic diversity and post-assembly modifications (e.g., glucosylation, acetylation) further alter immunogenicity and serotype features. The O-antigen is a potent virulence factor, enabling resistance to complement-mediated killing, masking other immunogenic surface structures, and aiding environmental persistence and transmission. It is the primary antigenic determinant for Salmonella serotyping and a main candidate for vaccine development, with O-antigen-protein conjugates and GMMA-based systems under investigation for broad, cross-serovar protection. The heterogeneity and immune-modulatory roles of the O-antigen make it both a valuable therapeutic target and a persistent challenge in bacterial vaccine design.

Other names

O-antigenO-polysaccharide (O-PS, OPS)Group IV capsule (historically as “O-antigen capsule” in Salmonella)

Induction of opsonophagocytic antibodies facilitating immune recognition and clearance of Salmonella Neutralization of polysaccharide antigen via antibody binding Elicitation of cross-protective immunity across serovars