Structural and Serological Characterization of Yet Another New O Antigen, O86, in Proteus mirabilis Clinical Strains

Bacteria from the genus <i>Proteus</i> are facultative human pathogens, primarily attacking the urinary tract and wounds. A total of 85 O serogroups have been identified so far among these bacilli. <i>P. mirabilis</i> Bprz 86 was isolated from the fistula of a patient in Łódź, Poland. Enzyme-Linked Immunosorbent Assay (ELISA) and Western blotting studies involving the <i>P. mirabilis</i> Bprz 86 lipopolysaccharide (LPS) and the strain-specific rabbit antiserum indicated that the strain, which does not belong to any of the O1-O85 serogroups, shares a common epitope with <i>Proteus</i> O17 antigens and is identical to another clinical <i>P. mirabilis</i> strain, Sm 120, isolated from the urine of a patient in the area. The O-specific polysaccharide (O antigen) was obtained from <i>P. mirabilis</i> Bprz 86 LPS through mild acid degradation, and the six-constituent structure of its repeating unit was determined using chemical analyses and 1D and 2D ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. It includes (<i>R</i>)-3-hydroxybutanoyl, which, along with fucosamine and glucose residues, forms a fragment also present in the O17 antigens. Based on the obtained serological and chemical data, the two studied <i>P. mirabilis</i> isolates were proposed as candidates for a new successive O serogroup in the genus <i>Proteus</i>, O86.