INHIBITION OF CELL-WALL TURNOVER AND AUTOLYSIS BY VANCOMYCIN IN A HIGHLY VANCOMYCIN-RESISTANT MUTANT OF STAPHYLOCOCCUS-AUREUS

A highly vancomycin-resistant mutant (MIG = 100 (mu g/ml) of Staphyloc occus aureus, mutant VM, which was isolated in the laboratory by a ste p-pressure procedure, continued to grow and synthesize peptidogiycan i n the presence of vancomycin (50 mu g/ml) in the medium, but the antib iotic completely inhibited cell wall turnover and autolysis, resulting in the accumulation of cell wall material at the cell surface and inh ibition of daughter cell separation, Cultures of mutant VM removed van comycin from the growth medium through binding the antibiotic to the c ell walls, from which the antibiotic could be quantitatively recovered in biologically active form, Vancomycin blocked the in vitro hydrolys is of cell walls by autolytic enzyme extracts, lysostaphin and mutanol ysin, Analysis of UDP-linked peptidoglycan precursors showed no eviden ce for the presence of D-lactate-terminating muropeptides. While there was no significant difference in the composition of muropeptide units of mutant and parental cell walls, the peptidoglycan of VM had a sign ificantly lower degree of crosslinkage, These observations and the res ults of vancomycin-binding studies suggest alterations in the structur al organization of the mutant cell walls such that access of the vanco mycin molecules to the sites of wall biosynthesis is blocked.