Structure of the O-polysaccharide of Proteus mirabilis OC (CCUG 10702) from a new proposed Proteus serogroup O75

A neutral O-polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Proteus mirabilis OC (CCUG 10702) and studied by sugar and methylation analyses and 1H and 13C NMR spectroscopy. The following structure of the tetrasaccharide repeating unit of the polysaccharide was established: Based on the unique structure of the O-polysaccharide and serological data, we propose classifying P. mirabilis OC (CCUG 10702) into a new separate Proteus serogroup O75. A weak cross-reaction of O-antiserum against P. mirabilis OC with the lipopolysaccharide of P. mirabilis O49 was accounted for by a similarity in the O-polysaccharide structures.