BAY 11-7082 potentiates select β-lactams to inhibit growth of methicillin-resistant Staphylococcus aureus

ABSTRACT β-lactams are an important class of antibiotics that target penicillin-binding proteins (PBPs) essential to bacterial cell wall synthesis. They are used to treat serious bacterial infections, including those caused by the versatile pathogen Staphylococcus aureus . Some strains carry the resistance gene, mecA, encoding a β-lactam-insensitive PBP2A that allows for peptidoglycan synthesis in the presence of β-lactams like methicillin, limiting treatment options. We previously identified BAY 11-7082 as having antibacterial activity against methicillin-resistant S. aureus (MRSA) and showed that it re-sensitizes MRSA to β-lactams like penicillin G, making BAY 11-7082 and its analogues promising candidates for the development of an antibiotic adjuvant. Although the direct antibacterial mechanism of BAY 11-7082 remains undefined, here we aimed to better understand how it potentiates β-lactam activity. We tested BAY 11-7082 in combination with a variety of β-lactams and identified a subset that were synergistic in MRSA but not methicillin-susceptible S. aureus , suggesting they may directly or indirectly impact the function of PBP2A. Electron and fluorescence microscopy studies revealed that unlike other β-lactam adjuvants, such as those that target the biosynthesis of wall teichoic acids (WTAs), BAY 11-7082 failed to impact cell division, disrupt PBP2 localization, or activate a sensitive reporter of cell wall damage. However, the production of WTA was necessary for BAY 11-7082-β-lactam synergy. Together these data suggest its mechanism of β-lactam potentiation is distinct from known compounds, making BAY 11-7082 a useful tool to better understand the complexity of resistance in MRSA.