Penicillin binding protein 4 (PBP4) can provide high-level β-lactam resistance in A series of missense and promoter mutations associated with were detected in strains that displayed high-level resistance. We show here that the missense mutations facilitate the β-lactam resistance mediated by PBP4 and the promoter mutations lead to overexpression of Our results also suggest a cooperative interplay among PBPs for β-lactam resistance.

bStaphylococcus aureus is an important cause of both hospital-and community-associated methicillin-resistant S. aureus (MRSA) infections worldwide. ␤-Lactam antibiotics are the drugs of choice to treat S. aureus infections, but resistance to these and other antibiotics make treatment problematic. High-level ␤-lactam resistance of S. aureus has always been attributed to the horizontally acquired penicillin binding protein 2a (PBP 2a) encoded by the mecA gene. Here, we show that S. aureus can also express high-level resistance to ␤-lactams, including new-generation broad-spectrum cephalosporins that are active against methicillin-resistant strains, through an uncanonical core genome-encoded penicillin binding protein, PBP 4, a nonessential enzyme previously considered not to be important for staphylococcal ␤-lactam resistance. Our results show that PBP 4 can mediate high-level resistance to ␤-lactams.