Effective Membrane Permeabilization of Methicillin-Resistant <i>Staphylococcus aureus</i> by Prenylated Phenolics

Prenylated phenolics are plant-derived compounds with antimicrobial activity against methicillin-resistant <i>Staphylococcus aureus</i> (MRSA), acting by targeting membranes resulting in fast permeabilization. Studies quantifying their membrane permeabilization capacity are lacking, limiting our understanding of the structural properties driving this effect. This study evaluated antimicrobial activity and permeabilization efficacy of 36 C- and O-prenylated phenolics, including 11 C- and O-prenylated phenolics chemically synthesized for this study. Minimum inhibitory concentrations (MICs) were obtained using the broth microdilution assay. Membrane permeabilization was measured by propidium iodide uptake using fluorescence spectrometry and microscopy. The most potent MRSA permeabilizers were luteone (<b>29</b>) and neobavaisoflavone (<b>22</b>), with EC₁₀ of 27 ± 7 and 28 ± 8 μg mL^-1, respectively. Diprenylated phenolics showed a strong negative correlation between permeabilization and their hydrophobic-to-polar surface area ratio (<i>r</i>_pearson = 0.88). For monoprenylated phenolics, prenyl configuration (chain) and molecular shape (globular) were important for effective permeabilization. Interestingly, potency of antimicrobial prenylated phenolics (MIC ≤ 50 μg mL^-1) was not correlated to permeabilization potency, suggesting other mechanisms of action in addition to membrane permeabilization. These quantitative findings on membrane permeabilization by prenylated phenolics contribute to our mechanistic understanding of how these compounds can inhibit microbial growth.