MODIFICATION OF PEPTIDOGLYCAN PRECURSORS IS A COMMON FEATURE OF THE LOW-LEVEL VANCOMYCIN-RESISTANT VANB-TYPE ENTEROCOCCUS D366 AND OF THE NATURALLY GLYCOPEPTIDE-RESISTANT SPECIES LACTOBACILLUS-CASEI, PEDIOCOCCUS-PENTOSACEUS, LEUCONOSTOC-MESENTEROIDES, AND ENTEROCOCCUS-GALLINARUM

The biochemical basis for the acquired or natural resistance of variou s gram-positive organisms to glycopeptides was studied by high-pressur e liquid chromatographic analysis of their peptidoglycan UDP-MurNAc-pe ptide precursors. In all cases, resistance was correlated with partial or complete replacement of the C-terminal D-Ala-D-Ala-containing UDP- MurNAc-pentapeptide by a new precursor with a modified C terminus. Nuc lear magnetic resonance analysis by sequential assignment showed that the new precursor encountered in Enterococcus faecium D366, a strain b elonging to the VANB class, which expresses low-level resistance to va ncomycin, was DP-MurNAc-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-lactate, ident ical to that previously found in the VANA class, which expresses high- level resistance to vancomycin. High-pressure liquid chromatographic a nalyses, composition determinations, and digestion by R39 D,D-carboxyp eptidase demonstrated the exclusive presence of the new precursor in L actobacillus casei and Pediococcus pentosaceus, which are naturally hi ghly resistant to glycopeptides. The low-level natural resistance of E nterococcus gallinarum to vancomycin was found to be associated with t he synthesis of a new precursor identified as a UDP-MurNAc-pentapeptid e containing a C-terminal D-serine. The distinction between low and hi gh levels of resistance to glycopeptides appeared also to depend on th e presence or absence of a substantial residual pool of a D-Ala-D-Ala- containing UDP-MurNAc-pentapeptide.