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 Plesiomonas shigelloides 78/89 lipopolysaccharide directly on bacteria revealed the characteristic structural features of the O-acetylated polysaccharide in the NMR spectra. The O-antigen profiles were unique, yet the pattern of signals in the, spectra along with their (1)H,(13)C chemical shift values, resembled these of d-galactan I of Klebsiella pneumoniae. The isolated O-specific polysaccharide (O-PS) of P. shigelloides strain CNCTC 78/89 was investigated by (1)H and (13)C NMR spectroscopy, mass spectrometry and chemical methods. The analyses demonstrated that the P. shigelloides 78/89 O-PS is composed of →3)-α-d-Galp-(1→3)-β-d-Galf2OAc-(1→ disaccharide repeating units. The O-acetylation was incomplete and resulted in a microheterogeneity of the O-antigen. This O-acetylation generates additional antigenic determinants within the O-antigen, forms a new chemotype, and contributes to the epitopes recognized by the O-serotype specific antibodies. The serological cross-reactivities further confirmed the inter-specific structural similarity of these O-antigens.