Salmonella enterica serovar Typhimurium O-antigen (STM O-antigen)

The O-specific polysaccharide (OPS), also known as the O-antigen, is the outermost carbohydrate component of the lipopolysaccharide (LPS) located on the cell surface of Salmonella enterica serovar Typhimurium [2, 8]. In S. Typhimurium, which belongs to serogroup B, this molecule is characterized by a repeating oligosaccharide unit typically consisting of mannose, rhamnose, and galactose, with an abequose side-branch defining the immunodominant O4 factor [5, 20]. Biologically, the O-antigen serves as a vital virulence factor by providing a physical and chemical shield that protects the bacterium from the host's innate immune defenses, including complement-mediated lysis and phagocytic uptake [7, 22]. In human pathology, S. Typhimurium is a primary driver of invasive non-typhoidal Salmonella (iNTS) disease, which manifests as life-threatening systemic infections in pediatric and immunocompromised populations [1, 4]. Due to its high surface exposure and immunogenicity, the O-antigen is the central target for various experimental vaccines, including glycoconjugates and Generalized Modules for Membrane Antigens (GMMA) [2, 11, 13]. These therapeutic candidates aim to elicit high-affinity bactericidal antibodies that neutralize the pathogen [11, 14]. However, the T-independent nature of the polysaccharide necessitates its conjugation to carrier proteins to ensure long-term immunological memory and protection in young children [5, 16].

Other names

O-specific polysaccharide of Salmonella enterica serovar TyphimuriumSTM O-polysaccharideSTM O-specific polysaccharideSomatic O-antigenO-side chainO-antigen 4, 5, 12

Vaccine antigens targeting this molecule induce the production of O-antigen-specific bactericidal and opsonophagocytic antibodies (IgG, IgM, and IgA) that facilitate the clearance of the bacteria by the host immune system [2, 5, 11].