Structural Masquerade of Plesiomonas shigelloides Strain CNCTC 78/89 O-Antigen-High-Resolution Magic Angle Spinning NMR Reveals the Modified d-galactan I of Klebsiella pneumoniae.

The high-resolution magic angle spinning nuclear magnetic resonance spectroscopy (HR-MAS NMR) analysis of 78/89 lipopolysaccharide directly on bacteria revealed the characteristic structural features of the -acetylated polysaccharide in the NMR spectra. The -antigen profiles were unique, yet the pattern of signals in the, spectra along with their ¹H,C chemical shift values, resembled these of d-galactan I of . The isolated specific polysaccharide (O-PS) of strain CNCTC 78/89 was investigated by ¹H and C NMR spectroscopy, mass and chemical methods. The analyses demonstrated that the 78/89 PS is composed of →3)-α-d-Gal-(1→3)-β-d-Gal2OAc-(1→ disaccharide repeating units. The acetylation was incomplete and resulted in a microheterogeneity of the antigen. This acetylation generates additional antigenic determinants within the antigen, forms a new chemotype, and contributes to the epitopes recognized by the serotype specific antibodies. The serological cross-reactivities further confirmed the inter-specific structural similarity of these antigens.