Effect of lauric acid on efflux pump inhibition in Staphylococcus aureus K2068: Regulation of the mepA gene and membrane permeability alterations

MepA efflux protein found in Staphylococcus aureus belongs to the MATE (Multidrug and Toxic Compound Extrusion) family and plays an important role in bacterial resistance. We investigated the potential of lauric acid as an inhibitor of the MepA efflux pump by means of Minimum Inhibitory Concentration (MIC) assays and modulation of the MICs of ciprofloxacin and ethidium bromide (EtBr) against S. aureus; the compound's ability to increase the fluorescence of EtBr and Sytox Green, as well as its ability to inhibit the expression of the mepA gene. The results showed that lauric acid had no antibacterial effect against S. aureus K2068. When combined with ciprofloxacin, the compound potentiated the effect of the antibiotic, reducing the MIC from 64 to 32 μg/mL and increasing the fluorescence of EtBr and Sytox Green, suggesting inhibition of MepA and greater permeabilization of the cell membrane. Furthermore, qPCR assays revealed that lauric acid promoted a reduction in mepA gene expression. Molecular docking indicated that lauric acid interacts with the efflux pump in a similar way to chlorpromazine through hydrophobic interaction with the Phe153 residue. ADME modeling suggested that lauric acid's moderate lipophilicity favors passive cell permeability. The results of the toxicity assays in D. melanogaster indicate that lauric acid and ciprofloxacin exhibit low toxicity in the evaluated model. Together, these findings suggest that lauric acid could be a promising antibiotic adjuvant and MepA efflux pump inhibitor in S. aureus.