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

Abstract

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. 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. and 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.