4-AMINO-4-DEOXY-L-ARABINOSE IN LPS OF ENTEROBACTERIAL R-MUTANTS AND ITS POSSIBLE ROLE FOR THEIR POLYMYXIN REACTIVITY

The content of 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N) and the ph osphate substitution pattern of the LPS of various strains from Salmon ella minnesota, Yersinia enterocolitica and Proteus mirabilis was dete rmined by GC/MS, HPLC and P-31-NMR. These data allowed us to examine t he possible role of these components for the polymyxin B-binding capac ity 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 Re-mutants of S. minnesota, strain R595 (Re-mutant) showed about a 90 % substitution of the eater-linked phosphate-group with L-Arap4N, wher eas the L-Arap4N content of the other S. minnesota strains amounted to 17-25%. Neither the binding capacity of LPS to polymyxin B, determine d by a bioassay, nor the MIC- and MBC-values of the R-mutants were sig nificantly 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 eater-linked phosphate group were pr epared and subjected to the polymyxin-binding assay. The results obtai ned so far indicated that the inner core bound L-Arap4N, detected in a ll resistant strains investigated, may play a decisive role in the dec reased binding of polymyxin B, responsible for the bacterial resistanc e towards polymyxin(s).