O-polysaccharide of Salmonella enterica serovar Enteritidis (O-Ag (for O-antigen), OPS (for O-polysaccharide))

The O-polysaccharide of Salmonella enterica serovar Enteritidis, also known as the O-antigen, is a repetitive glycan polymer that constitutes the outermost domain of the LPS molecule on the bacterial surface. It is composed of repeating units of sugars—mannose, rhamnose, galactose, and tyvelose (the latter conferring the O:9 serotype specificity)[2][6]. This structure serves as a major antigenic determinant for the classification of Salmonella serovars and acts as both a virulence factor and a protective antigen. The O-antigen allows the bacterium to evade immune detection and contributes to resistance against complement-mediated lysis and phagocytosis. It is the principal target for vaccine strategies aiming to prevent Salmonella enterica infections, including conjugate vaccines that elicit protective antibody responses[2][6]. The O-antigen capsule, a structure highly similar to the LPS O-polysaccharide, also plays a role in environmental persistence and transmission[3][4]. There are no direct small-molecule inhibitors of O-polysaccharide, making anti-OPS immunity an indirect but critical therapeutic and preventive strategy.

Other names

O-antigen of S. EnteritidisO-specific polysaccharide (OSP)O-Ag (O-antigen)Group D1 O-antigenSalmonella Enteritidis O-polysaccharide

Induction of O-antigen–specific protective antibodies leading to opsonophagocytosis, complement-mediated killing, and protective immunity