Two codependent routes lead to high-level MRSA.

Methicillin-resistant (MRSA), in which acquisition of [which encodes the cell wall peptidoglycan biosynthesis component penicillin-binding protein 2a (PBP2a)] confers resistance to β-lactam antibiotics, is of major clinical concern. We show that, in the presence of antibiotics, MRSA adopts an alternative mode of cell division and shows an 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 () mutations. MRSA resensitizing agents differentially interfere with the two codependent mechanisms required for high-level antibiotic resistance, which provides opportunities for new interventions.