Structural Studies of the Lipopolysaccharide of Aeromonas veronii bv. sobria Strain K133 Which Represents New Provisional Serogroup PGO1 Prevailing among Mesophilic Aeromonads on Polish Fish Farms.

In the present work, we performed immunochemical studies of LPS, especially the O-specific polysaccharide (O-PS) of Aeromonas veronii bv. sobria strain K133, which was isolated from the kidney of carp (Cyprinus carpio L.) during an outbreak of motile aeromonad infection/motile aeromonad septicemia (MAI/MAS) on a Polish fish farm. The structural characterization of the O-PS, which was obtained by mild acid degradation of the LPS, was performed with chemical methods, MALDI-TOF mass spectrometry, and 1H and 13C NMR spectroscopy. It was revealed that the O-PS has a unique composition of a linear tetrasaccharide repeating unit and contains a rarely occurring sugar 2,4-diamino-2,4,6-trideoxy-D-glucose (bacillosamine), which may determine the specificity of the serogroup. Western blotting and ELISA confirmed that A. veronii bv. sobria strain K133 belongs to the new serogroup PGO1, which is one of the most commonly represented immunotypes among carp and trout isolates of Aeromonas sp. in Polish aquacultures. Considering the increase in the MAI/MAS incidences and their impact on freshwater species, also with economic importance, and in the absence of an effective immunoprophylaxis, studies of the Aeromonas O-antigens are relevant in the light of epidemiological data and monitoring emergent pathogens representing unknown antigenic variants and serotypes.

Structure of the disaccharide repeating unit of O-specific polysaccharide isolated from Aeromonas veronii strain Bs8 pathogenic to common carp (Cyprinus carpio).

The O-specific polysaccharide (OPS) was isolated from the lipopolysaccharide of Aeromonas veronii strain Bs8, which is pathogenic to common carp (Cyprinus carpio), after mild acid hydrolysis followed by gel-permeation chromatography. The high-molecular-mass OPS fraction was investigated using chemical methods, mass spectrometry, and 1H and 13C NMR spectroscopy techniques, including 2D homonuclear 1H,1H TOCSY, DQF COSY, NOESY, and heteronuclear 1H-detected 1H,13C HSQC, and HMBC experiments. The analysis revealed that the O-specific polysaccharide contains sugars with the galacto configuration of the ring and is composed of a disaccharide repeating unit with the following structure.