Structural and serological studies on the O‐antigen of Proteus mirabilis O14, a new polysaccharide containing 2‐[(R)‐1‐carboxyethylamino]ethyl phosphate

An O‐specific polysaccharide was obtained by mild acid degradation of Proteus mirabilis O14 lipopolysaccharide (LPS) and found to contain d‐galactose, 2‐acetamido‐2‐deoxy‐d‐glalactose, phosphate, N‐(2‐hydroxyethyl)‐d‐alanine (d‐AlaEtn), and O‐acetyl groups. Studies of the initial and O‐deacetylated polysaccharides using one‐ and two‐dimensional 1H‐ and 13C‐NMR spectroscopy, including COSY, TOCSY, NOESY, H‐detected 1H,13C heteronuclear multiple‐quantum coherence, and heteronuclear multiple‐bond correlation experiments, demonstrated the following structure of the repeating unit: This is the second bacterial polysaccharide reported to contain α‐d‐Galp6PAlaEtn, whereas the first one was the O‐antigen of P. mirabilis EU313 taken erroneously as strain PrK 6/57 from the O3 serogroup [Vinogradov, E. V., Kaca, W., Shashkov, A.S., Krajewska‐Pietrasik, D., Rozalski, A., Knirel, Y.A. & Kochetkov, N.K. (1990) Eur. J. Biochem.,188, 645–651]. Anti‐(P. mirabilis O14) serum cross‐reacted with LPS of P. mirabilis EU313 and vice versa in passive hemolysis and ELISA. Absorption of both O‐antisera with the heterologous LPS decreased markedly but did not abolish the reaction with the homologous LPS. These and chemical data indicated that both strains have similar but not identical O‐antigens. Therefore, we propose that P. mirabilis EU313 should belong to a new subgroup of the O14 serogroup.