Olikomycin A Disrupts Gram-Positive Bacterial Membranes Through Calcium-Dependent Binding to Phosphatidylglycerol.

Calcium-dependent antibiotics (CDAs) represent an important class of antimicrobial agents active against Gram-positive pathogens. Olikomycin A, produced by Streptomyces ghanaensis ΔwblA, displays potent activity against multidrug-resistant bacteria; however, its molecular mode of action remained unclear. In this study, we investigated the interaction of olikomycin A with bacterial membrane lipids. Phospholipid antagonization assays demonstrated a calcium-dependent interaction with phosphatidylglycerol (PG), a major anionic phospholipid of Gram-positive membranes. Cryo-electron microscopy and fluorescence microscopy using model membranes revealed rapid membrane disruption induced by olikomycin A, resulting in vesicle deformation and fragmentation. Compared with the clinically used lipopeptide daptomycin, olikomycin A caused markedly faster and more extensive membrane damage. Furthermore, treatment of Staphylococcus aureus with olikomycin A in the presence of calcium resulted in rapid cellular aggregation consistent with severe membrane perturbation. These findings indicate that olikomycin A targets bacterial membranes via calcium-dependent binding to PG and disrupts membrane integrity through a mechanism distinct from daptomycin.