Salmonella enterica serovar Paratyphi A O:2 O-antigen (O:2 OAg) (O:2 OAg)

The O:2 O-antigen is the O-specific polysaccharide (OSP) component of the lipopolysaccharide (LPS) located on the outer membrane of Salmonella enterica serovar Paratyphi A [1]. It serves as a critical virulence factor and is the primary target for the development of vaccines against paratyphoid fever, a systemic infection that remains a significant public health burden in South and Southeast Asia [2, 4]. The O:2 antigen structure consists of a trisaccharide backbone of rhamnose, mannose, and galactose, with a terminal paratose residue that confers its serogroup A specificity [1, 3]. In vaccine development, this polysaccharide is often conjugated to carrier proteins such as CRM197 or tetanus toxoid to enhance its immunogenicity and induce a T-cell dependent immune response [3, 5]. These conjugate vaccines aim to elicit high levels of bactericidal antibodies that promote the clearance of the bacteria via the complement system and opsonophagocytosis [2, 3]. Clinical trials are currently evaluating bivalent formulations that combine the O:2 antigen with the Vi polysaccharide of S. Typhi to provide broad protection against enteric fever [5]. (Sources: [1] NIH/PubMed 24631090; [2] MDPI Vaccines 13(2):122; [3] MDPI Vaccines 12(11):1264; [4] WHO Paratyphoid Pipeline; [5] University of Oxford/NEJM 2025).

Other names

O-specific polysaccharideOSPO:2 antigenSalmonella Paratyphi A LPS O-antigenGroup A O-antigen

Induction of protective bactericidal antibodies (IgG and IgA) that target the O-antigen on the bacterial surface, facilitating complement-mediated lysis and opsonophagocytosis of Salmonella Paratyphi A.