Characterization of the lipopolysaccharide O-antigen of Francisella novicida (U112)

Francisella novicida (U112), a close relative of the highly virulent bacterium F. tularensis, was shown to produce a lipopolysaccharide in which the antigenic O-polysaccharide component was found by chemical, 1H and 13C NMR and MS analyses to be an unbranched neutral linear polymer of a repeating tetrasaccharide unit composed of 2-acetamido-2-deoxy-D-galacturonamide (D-GalNAcAN) and 2,4-diacetamido-2,4,6-trideoxy-D-glucose (D-Qui2NAc4NAc, di-N-acetylbacillosamine) residues (3:1) and had the structure: -->4)-alpha-D-GalNAcAN-(1-->4)-alpha-D-GalNAcAN-(1-->4)-alpha-D-GalNAcAN-(1-->3)-alpha-D-QuiNAc4NAc-(1-->. With polyclonal murine antibody, the F. novicida O-antigen did not show serological cross-reactivity with the O-antigen of F. tularensis despite the occurrence of a common -->4)-D-GalpNAcAN-(1-->4)-alpha-D-GalpNAcAN-(1--> disaccharide unit in their respective O-antigens. Thus, O-PS serology offers a practical way to distinguish between the two Francisella species.