Two co-dependent routes lead to high-level MRSA

Methicillin-resistant S. aureus (MRSA) is of major clinical concern, in which acquisition of mecA, encoding the cell wall peptidoglycan biosynthesis component Penicillin Binding Protein 2a (PBP2a), confers resistance to β-lactam antibiotics. In the presence of antibiotics, we show that MRSA adopts an alternative cell division mode, with altered peptidoglycan architecture at the division septum. PBP2a can replace the transpeptidase activity of the endogenous and essential PBP2, but not that of PBP1, which is responsible for the distinctive native septal peptidoglycan architecture. Successful division without PBP1 activity requires the alternative division mode and is enabled by several possible chromosomal, potentiator (pot) mutations. MRSA resensitizing agents differentially interfere with the two co-dependent mechanisms required for high-level antibiotic resistance, providing opportunities for new interventions.