ANALYSIS OF 7-SUBSTITUTED SIALIC-ACID IN SOME ENTEROBACTERIAL LIPOPOLYSACCHARIDES

Sialic acid-containing lipopolysaccharides (LPS) were isolated from six bacterial strains of the family Enterobacteriaceae. Sialic acid was released from permethylated LPS by methanolysis, and partially O-methylated N-acetyl-N-methyl-neuraminic acid methyl ester methyl glycosides were analyzed by gas-liquid chromatography-electron ionization mass spectrometry. It was proved that all LPS contain N-acetylneuraminic acid (NeuAc). The occurrence of 7-substituted NeuAc in Escherichia coli serotypes 024 and 056 and in Citrobacter freundii 037 LPS was documented. The LPS preparations also contained terminal NeuAc. LPS of E. coli 0104 had exclusively 4-substituted sialic acid. The remaining LPS studied, namely, from Salmonella toucra 048 and Hafnia alvei 2, had 4-linked and terminally localized NeuAc residues.