Structure of the O-polysaccharide of a serologically separate strain of Proteus mirabilis, TG 332, from a new proposed Proteus serogroup O50.

The O-polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Proteus mirabilis TG 332 strain. The following structure of the O-polysaccharide was determined by chemical methods along with NMR spectroscopy, including 2D COSY, TOCSY, ROESY and 1H, 13C HMQC experiments: [see equation in text]. The O-polysaccharide studied has a unique structure among Proteus O-antigens. Accordingly, P. mirabilis TG 332 is serologically separate, and we propose to classify this strain into a new Proteus serogroup, O50. The nature of minor epitopes that provide a cross-reactivity of P. mirabilis TG 332 O-antiserum with the LPS of P. mirabilis O30 and Proteus penneri 34 (O60) is discussed.