Structure of the lipopolysaccharide O-antigen of Aeromonas encheleia strain A4 representing the new PGO1 serogroup of aeromonads prevailing in Polish aquaculture.

The structure of the O-specific polysaccharide (OPS) from Aeromonas encheleia strain A4 lipopolysaccharide was investigated. A. encheleia strain A4, classified into the new provisional serogroup PGO1 predominating among aeromonads in Polish aquaculture, was isolated from common carp tissues during an outbreak of MAI/MAS disease on a fish farm. The high-molecular-weight OPS fraction liberated from the lipopolysaccharide after mild acid hydrolysis followed by gel-permeation chromatography was studied with chemical methods, mass spectrometry, and one- and two-dimensional H and C NMR spectroscopy techniques. Inter-residue correlations were identified in H,C-heteronuclear multiple-bond correlation (HMBC) and H,H NOESY experiments. It was found that the O-specific polysaccharide of A. encheleia strain A4 consists of branched pentasaccharide repeating units with the following structure:→2)[α-d-Fucp3NRHb-(1→3)]-α-l-Rhap-(1→3)-β-l-Rhap-(1→4)-α-l-Rhap-(1→3)-β-d-QuipNAc-(1→.