4-amino-4-deoxyarabinose and 2-keto-3-deoxyoctonate

The content of 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N) and the phosphate substitution pattern of the LPS of various strains from Salmonella minnesota, Yersinia enterocolitica and Proteus mirabilis was determined by GC/MS, HPLC and 31P-NMR. These data allowed us to examine the possible role of these components for the polymyxin B-binding capacity of LPS and for the minimal inhibiting concentration (MIC) and the minimal bactericidal concentration (MBC) of polymyxins B and E towards the respective R-mutants. Contrary to other investigated Re-, Rd- and Rc-mutants of S. minnesota, strain R595 (Re-mutant) showed about a 90% substitution of the ester-linked phosphate-group with L-Arap4N, whereas the L-Arap4N content of the other S. minnesota strains amounted to 17-25%. Neither the binding capacity of LPS to polymyxin B, determined by a bioassay, nor the MIC- and MBC-values of the R-mutants were significantly affected by this alteration. Similar results were obtained after using the temperature-dependent changes in the L-Arap4N-content and phosphate substitution pattern of Y. enterocolitica 75R. In order to explore the relevant polymyxin B binding site, lipid A samples with or without substitution of their ester-linked phosphate group were prepared and subjected to the polymyxin-binding assay. The results obtained so far indicated that the inner core bound L-Arap4N, detected in all resistant strains investigated, may play a decisive role in the decreased binding of polymyxin B, responsible for the bacterial resistance towards polymyxin(s).

Topics: Amino Sugars; Enterobacteriaceae; Lipid A; Lipopolysaccharides; Microbial Sensitivity Tests; Mutation; Polymyxins; Sugar Acids

Contrary to previous reports, lipopolysaccharides from Pseudomonas cepacia contain a 3-deoxyoct-2-ulosonic acid (probably a single residue). The lipopolysaccharides contain only two phosphate residues, one of which apparently forms a phosphodiester bridge between 4-amino-4-deoxyarabinose and a glucosamine residue in lipid A. The second, unlocated phosphate residue occurs mainly as a monoester in some lipopolysaccharides, and mainly as a diester in others. All lipopolysaccharides lack pyrophosphate residues. The results support the view that the resistance of P. cepacia to cationic antibiotics stems from ineffective binding to the outer membrane, as a consequence of the low number of phosphate and carboxylate groups in the lipopolysaccharide, and the presence of the protonated aminodeoxypentose.

Topics: Amino Sugars; Anti-Bacterial Agents; Carbohydrate Sequence; Cations; Drug Resistance, Microbial; Lipopolysaccharides; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Phosphates; Pseudomonas; Sugar Acids