Clioquinol derivatives as potent inhibitors of Methicillin-Resistant Staphylococcus aureus and their mechanistic study

Aims: Methicillin-Resistant Staphylococcus aureus cause many nosocomial, and community-acquired infections, burdening healthcare systems globally. The aim of the current study was to identify the potent inhibitors of MRSA strains as first step towards drug discovery against MRSA related infections. Methods and Results: Clioquinol derivatives 1–10 were evaluated against MRSA strains, using microplate alamar blue assay (MABA). Among them compounds 1–3, and 6–8 were found to be active with MIC values within the range of 61.08–213.58 µM. Compounds 1, and 7 were found highly potent with MIC values of 64.04 and 61.08 µM, respectively. Both these compounds also showed non-covalent interactions with active site key residues of topoisomerase IV enzyme in molecular docking studies. Mechanisms of action of the most active compounds 1, and 7 were further studied through AFM, and fluorescence microscopy. It was observed that compounds 1, and 7 caused a massive destruction in shape, and greatly reduced the size and number of viable cells. Flow cytometry analysis showed a significant rise in DiBAC4(3) fluorescence, and a non-significant rise in PI fluorescence indicating increased bacterial membrane depolarization of treated cells. Most importantly the clioquinol derivatives 1, and 7 did not cause any hemolytic effect. Moreover, all the compounds were found to be non-cytotoxic to BJ (Human fibroblast) normal cell line. Conclusion: Our findings suggest that clioquinol derivatives 1, and 7 possess highly potent antibacterial activity against three MDR, and one sensitive strains of S. aureus. Significance and impact of the study: Clioquinol derivatives 1, and 7 could be further studied as potential antibacterial agents.