O-specific polysaccharide of Salmonella enterica serovar Enteritidis (OAg)

The O-specific polysaccharide (O-antigen) is a highly variable surface-exposed glycan that forms the outermost component of the lipopolysaccharide (LPS) in Salmonella enterica serovar Enteritidis. As a member of serogroup D1, its unique structure consists of a repeating trisaccharide backbone—comprising mannose, rhamnose, and galactose—with an immunodominant tyvelose side branch that confers the O:9 serological specificity [1, 6]. Biologically, this polysaccharide is essential for bacterial virulence, acting as a physical barrier that prevents host complement-mediated lysis and facilitates survival within the host environment [11, 12]. In clinical development, the O-specific polysaccharide serves as the primary target for next-generation glycoconjugate vaccines, such as the Trivalent Salmonella Conjugate Vaccine (TSCV), designed to prevent invasive nontyphoidal salmonellosis (iNTS) [2, 10]. These vaccines function by eliciting O-antigen-specific IgG antibodies that mediate opsonophagocytic killing and complement-mediated lysis of the pathogen [3, 5]. Success in targeting this molecule depends on effective detoxification of the parent lipopolysaccharide and conjugation to carrier proteins to induce robust T-cell dependent immunological memory [14, 16].

Other names

O-antigen of Salmonella EnteritidisSalmonella Enteritidis O-specific polysaccharideO-polysaccharide of Salmonella EnteritidisS. Enteritidis OAgSalmonella Enteritidis LPS O-antigenGroup D1 O-antigen

The O-specific polysaccharide is utilized as a protective antigen in conjugate vaccines. By linking the purified polysaccharide to a carrier protein, it induces the production of high-affinity IgG antibodies that bind to the O-antigen on the bacterial surface. This binding facilitates opsonization, enhances phagocytosis by immune cells, and triggers the classical complement pathway to eliminate the Salmonella bacteria.