Penicillin-binding proteins

Staphylococci possess 5 different membrane-bound penicillin-binding proteins (PBPs). These penicillin-binding proteins are necessary for the construction of the peptidoglycan cell wall of the bacteria. They cause the cross-linking of the peptidoglycan layers of the cell wall by a transpeptidation.

PBP2a is a penicillin-binding protein whose expression causes antibiotic resistance in methicillin-resistant S. aureus strains (= MRSA). PBP2a is encoded by the mecA gene, the methicillin resistance gene.

Betalactam antibiotics have a 1000-fold reduced affinity for the new PBP2a and can therefore no longer block it. As a result, cell wall synthesis continues undisturbed and the bacteria are not killed (methicillin-resistant S. aureus = MRSA). The methicillin resistance determined by the mecA gene leads to the loss of all penicillins, cephalosporins and carbapenems.