POINT MUTATIONS IN STAPHYLOCOCCUS-AUREUS PBP-2 GENE AFFECT PENICILLIN-BINDING KINETICS AND ARE ASSOCIATED WITH RESISTANCE

In Staphylococcus aureus, penicillin-binding protein 2 (PBP 2) has bee n implicated in non-PBP 2a-mediated methicillin resistance. The PBP 2 gene (bpbB) was cloned from an expression library of a methicillin sus ceptible strain of S. aureus (209P), and its entire sequence was compa red with that of the pbpB gene from strains BB255, BB255R, and CDC6. P oint mutations that resulted in amino acid substitutions near the cons erved penicillin-binding motifs were detected in BB255R and CDC6, two low-level methicillin-resistant strains. Penicillin binding to PBP 2 i n both BB255R and CDC6 is altered, and kinetic analysis indicated that altered binding of PBP 2 by penicillin was due to both lower binding affinity and more rapid release of bound drug. These structural and bi ochemical changes may contribute to the strains' resistance to beta-la ctam antibiotics.