PEPTIDOGLYCAN STRUCTURE OF ENTEROCOCCUS-FAECIUM EXPRESSING VANCOMYCINRESISTANCE OF THE VANB TYPE

Resistance to glycopeptide antibiotics in enterococci is due to the sy nthesis of UDP-MurNAc-tetrapeptide-D-lactate (where Mur is muramic aci d) replacing the normal UDP-MurNAc-pentapeptide precursor. The peptido glycan structures of an inducible VanB-type glycopeptide-resistant Ent erococcus faecium, D366, and its constitutively resistant derivative, MT9, were determined. Using HPLC, 17 muropeptides were identified and were present regardless of whether resistance was expressed or not. Th e structures of 15 muropeptides were determined using MS and amino aci d analysis. The cross-bridge between D-alanine and L-lysine consisted of one asparagine. No monomer pentapeptide or tetrapeptide-D-lactate c ould be identified. These results obtained with D366 (non-induced) and MT9 indicate that, in the absence of vancomycin, the cell wall synthe tic machinery of E. faecium can process the lactate-containing precurs or as efficiently as the normal pentapeptide. In contrast, the presenc e of subinhibitory inducing concentrations of vancomycin interfered wi th the synthesis of oligomers.