Identification and structural determination of the capsular polysaccharides from two Acinetobacter baumannii clinical isolates, MG1 and SMAL

The structures of the capsular polysaccharides (CPSs) of the two clinical isolates Acinetobacter baumannii SMAL and MG1 were elucidated. Hot phenol/water extractions of the dry biomasses, followed by enzymatic digestions and repeated ultracentrifugations led to the isolation of polysaccharides that were negative in Western blot analysis utilizing an anti-lipid A antibody, thus proving that they were not the LPS O-antigens but CPSs. Their structures were established on the basis of NMR spectroscopy and GC-MS analyses. The A. baumannii MG1 CPS consisted of a linear aminopolysaccharide with acyl substitution heterogeneity at the N-4 amino group of QuipN4N: 4)-alpha-D-GlcpNAc-(1 -> 4)-alpha-L-GalpNAcA-(1 -> 3)-beta-D-QuipNAc4NR-(1 -> R = -3-hydroxybutyrryl or acetyl. The repeating unit of the CPS produced by strain SMAL is a pentasaccharide, already reported for the O-antigen moiety from A. baumannii strain ATCC 17961: beta-D-GlcpNAc3NAcA-(1 down arrow 4) 6)-beta-D-Glcp-(1 -> 3)-beta-D-GalpNAc-(1 -> 3)-alpha-D-Galp-(1 -> 6)up arrow beta-D-GlcpNAc-(1