Structure of the O‐polysaccharide of Proteus penneri 28 and Proteus vulgaris O31 and classification of P. penneri 26 and 28 in Proteus serogroup O31

The lipopolysaccharides (LPS) of Proteus penneri 28 and Proteus vulgaris O31 (PrK 55/57) were degraded with dilute acetic acid and structurally identical high‐molecular‐mass O‐polysaccharides were isolated by gel‐permeation chromatography. Sugar analysis and nuclear magnetic resonance (NMR) spectroscopic studies showed that both polysaccharides contain d ‐GlcNAc, 2‐acetamido‐2,6‐dideoxy‐ l ‐glucose ( l ‐2‐acetamido‐2,6‐dideoxyglucose ( N ‐acetylquinovosamine)) and 2‐acetamido‐3‐ O ‐[( S )‐1‐carboxyethyl]‐2‐deoxy‐ d ‐glucose ( N ‐acetylisomuramic acid) and have the following structure:where ( S )‐1‐carboxyethyl [a residue of ( S )‐lactic acid] ( S ‐Lac) is an ether‐linked residue of ( S )‐lactic acid. The O‐polysaccharide studied is structurally similar to that of P. penneri 26, which differs only in the absence of S ‐Lac from the GlcNAc residue. Based on the O‐polysaccharide structures and serological data of the LPS, it was suggested classifying these strains in one Proteus serogroup, O31, as two subgroups: O(31a), 31b for P. penneri 28 and P. vulgaris PrK 55/57 and O31a for P. penneri 26. A serological relatedness of the LPS of Proteus O(31a), 31b and P. penneri 62 was revealed and substantiated by sharing epitope O31b, which is associated with N ‐acetylisomuramic acid. It was suggested that a cross‐reactivity of P. penneri 28 O‐antiserum with the LPS of several other P. penneri strains is due to a common epitope(s) on the LPS core.