INCREASED PRODUCTION OF PENICILLIN-BINDING PROTEIN-2, INCREASED DETECTION OF OTHER PENICILLIN-BINDING PROTEINS, AND DECREASED COAGULASE ACTIVITY ASSOCIATED WITH GLYCOPEPTIDE RESISTANCE IN STAPHYLOCOCCUS-AUREUS

The mechanism of glycopeptide resistance in the genus Staphylococcus i s unknown, Since these antimicrobial compounds act by binding the pept idoglycan precursor terminus, the target of transglycosylase and trans peptidase enzymes, it was hypothesized that resistance might be mediat ed in Staphylococcus aureus by increased production or activity of the se enzymes, commonly called penicillin-binding proteins (PBPs), To eva luate this possibility, glycopeptide-resistant mutants were prepared b y passage of several clinical isolates of this species in nutrient bro th containing successively increasing concentrations of the glycopepti de vancomycin or teicoplanin. Decreased coagulase activity and increas ed resistance to lysostaphin were uniformly present in the vancomycin- resistant mutants. Peptidoglycan cross-linking increased in one resist ant isolate and decreased in two resistant isolates, The amounts of ra dioactive penicillin that bound to each PBP in susceptible and resista nt strains were compared; PBP2 production was also evaluated by Wester n blotting, increased penicillin labeling and production of PBP2 were found in all resistant derivatives selected bg either vancomycin or te icoplanin, Moreover, the increase in PBP2 penicillin labeling occurred early in a series of vancomycin-selected derivatives and was strongly correlated (r > 0.9) with the increase in vancomycin and teicoplanin MIC. An increase in penicillin labeling also occurred, variably, in PB P1, PBP3, and/or PBP4. These data demonstrate a strong correlation bet ween resistance to glycopeptides and increased PUP activity and/or pro duction in S. aureus. Such an increase could allow PBPs to better comp ete with glycopeptides for the peptidoglycan precursor.