Penicillin-binding proteins of beta-lactam-resistant strains of Staphylococcus aureus. Effect of growth conditions.

Methicillin-resistant clinical isolates of Staphylococcus aureus are intrinsically resistant to beta-lactam antibiotics in that the resistance mechanism is unrelated to the possession of beta-lactamases. We have demonstrated that a new, high-molecular-mass penicillin-binding protein (PBP) is present in these strains with a low affinity for beta-lactams and that its amount is regulated by the growth conditions. The new PBP from all strains that have been examined has an identical mobility on SDS gel electrophoresis and is the only PBP still present in an uncomplexed state with beta-lactams (and therefore the only functional PBP when these strains are grown in media containing concentrations of beta-lactam antibiotics sufficient to kill sensitive strains.