Virtual screening and antimicrobial evaluation for identification of natural compounds as the prospective inhibitors of antibacterial drug resistance targets in Staphylococcus aureus

Infectious diseases have remained a burgeoning cause of death and disability since long. Staphylococcus aureus (S. aureus) is a severe bacterial pathogen causing nosocomial and community infections. It exhibits widespread resistance to antibiotics posing a significant threat to their efficacy. For combating this challenge, different strategies may include modifying existing antibiotics, developing new antibacterial agents, and combining treatments with resistance mechanism inhibitors. Resistance in S. aureus occurs through horizontal gene transfer or chromosomal mutations. Acquisition mechanisms involve enzymatic modification, efflux, target bypass, and drug displacement. Mutations can impact drug targets, activate efflux pumps, or alter cell wall composition to impede drug access. Overcoming S. aureus resistance requires innovative approaches to preserve antibiotic effectiveness. The present study involves the virtual screening of phytochemicals of diverse chemical classes from Zinc database against the antibiotic resistant targets of S. aureus like β-Lactamase, Penicillin Binding Protein 2a (PBP2a), Dihydrofolate reductase (DHFR), DNA gyrase, Multidrug ABC transporter SAV1866, Undecaprenyl diphosphate synthase (UPPS), etc. Thymol, eugenol, gallic acid, l-ascorbic acid, curcumin, berberine and quercetin were identified as potential molecules based on their docking score, binding interactions. These molecules were further analyzed for the ADMET and drug likeness properties using pkCSM, SwissADME and Qikprop tools. Further in vitro evaluation of these molecules against antibiotic-resistant strains of S. aureus, both alone and in combination with antibiotics revealed significant findings. Curcumin demonstrated the lowest MIC values (31.25-62.5 μg/ml) when tested individually. Thymol, berberine, and quercetin displayed MIC values within the range of 125-250 μg/ml, while eugenol and gallic acid exhibited MIC values ranging from 500 to 1000 μg/ml. Notably, thymol exhibited potent synergy with all four antibiotics against clinical isolates of S. aureus, with Fractional inhibitory concentration index (FICI) values consistently below 0.5, highlighting its exceptional antibacterial activity, especially in combination with amoxicillin.