Structural studies of the O-antigenic polysaccharides from the enteroaggregative Escherichia coli strain 522/C1 and the international type strain from Escherichia coli O178

Abstract

The structure of the O-antigenic polysaccharide (PS) from the enteroaggregative Escherichia coli strain 522/C1 has been determined. Component analysis and 1H and 13C NMR spectroscopy techniques were used to elucidate the structure. Inter-residue correlations were determined by 1H, 1H-NOESY and 1H, 13C-heteronuclear multiple-bond correlation experiments. The PS is composed of pentasaccharide repeating units with the following structure: → 4 ) - α - d - Glc p NAc - ( 1 → 4 ) - α - d - Gal p A - ( 1 → 2 ) - β - d - Rib f - ( 1 → 4 ) - β - d - Gal p - ( 1 → 3 ) - β - d - Gal p NAc - ( 1 → Analysis of NMR data reveals that on average the PS consists of four repeating units and indicates that the biological repeating unit contains an N-acetylgalactosamine residue at its reducing end. Serotyping of the E. coli strain 522/C1 showed it to be E. coli O178:H7. Determination of the structure of the O-antigen PS of the international type strain from E. coli O178:H7 showed that the two polysaccharides have identical repeating units. In addition, this pentasaccharide repeating unit is identical to that of the capsular polysaccharide from E. coli O9:K38, which also contains O-acetyl groups.