Abstract
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 1H,13C 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 1H and 13C 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.
Highlights
Plesiomonas shigelloides is a facultative anaerobic Gram-negative flagellated, rod-shaped bacterium belonging to the Enterobacteriaceae family [1]
The O-antigens of P. shigelloides 78/89 were initially investigated by high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy as the technique allows for the direct identification of the flexible O-antigen molecules on the bacterial cells in situ
The observed 1H resonances and 1H,13C-correlations in the HR-MAS NMR spectra of bacteria were further complemented by the HR-MAS NMR analysis of the isolated LPS
Summary
Plesiomonas shigelloides is a facultative anaerobic Gram-negative flagellated, rod-shaped bacterium belonging to the Enterobacteriaceae family [1] It is widely distributed in nature, but predominantly isolated from aquatic environments and animals [2]. LPS is a major component of the outer leaflet of the external membrane of Gram-negative bacteria These are amphiphilic molecules isolated from smooth bacterial strains (S-LPS). They can be divided into three distinct regions: lipid A, core oligosaccharide, and O-specific polysaccharide. The structural element α-L-Rhap(1→2)-α-L-Rhap described in S. flexneri serotype 6 is shared with P. shigelloides and Klebsiella pneumoniae O-antigens [29] In some aspects, this cross-reactivity of antibodies against the O-antigens is desirable as it can provide broad protection against heterologous bacteria
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