Unveiling the synergistic power of 3-hydrazinoquinoxaline-2-thiol and vancomycin against MRSA: An <i>in vitro </i>and <i>in silico</i> evaluation

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen causing infections ranging from skin disorders to severe conditions like infective endocarditis. Its evolving resistance, including resistance to β-lactams and last-resort antibiotics, such as vancomycin, daptomycin, and linezolid, necessitates alternative therapies. This study investigates the synergistic efficacy of vancomycin and 3-hydrazinoquinoxaline-2-thiol (3HL) against 23 clinical MRSA isolates. Susceptibility testing was performed using broth microdilution and checkerboard assays, while in silico analyses assessed interactions between vancomycin and 3HL. Vancomycin exhibited minimum inhibitory concentrations (MICs) ranging from 0.25 to 1 µg/mL, whereas 3HL showed higher MICs of 16-32 µg/mL. Synergistic interactions were confirmed via checkerboard assays, with fractional inhibitory concentration index (FICI) values between 0.236 and 0.5, indicating enhanced vancomycin efficacy. Notably, vancomycin MICs decreased significantly when combined with 3HL. In silico docking revealed interactions with penicillin-binding protein 2a (PBP2a), suggesting promising therapeutic potential. Vancomycin exhibited superior docking scores (-8.9 kcal/mol) and stabilizing hydrogen bonds, effectively targeting key protein grooves. Both compounds demonstrated potential for overcoming PBP2a's structural occlusions, suggesting their role in combating β-lactam-resistant strains through targeted protein inhibition and structural stabilization.