Thymol and Limonene as Potent Antimicrobials: Bridging In Vitro Efficacy and Molecular Docking Insights

Nowadays, antimicrobial resistance has created an urgent need for elaborating effective and novel antibiotic agents. In effect, bioactive compounds derived from plants have attracted great interest due to their biological activities. This work intended to study and compare the antimicrobial effect of thymol and limonene against multiple clinical microorganisms including gram-positive bacteria, gram-negative bacteria, yeasts, and mycobacteria. Molecular docking and bioavailability prediction of thymol and limonene were also performed. The in vitro study was realized via disk diffusion technique, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) assays. In parallel, in silico study of these compounds evaluated their drug-likeness, pharmacokinetic, and toxicity parameters, and binding to bacterial targets. Findings showed that thymol exhibited significantly greater antimicrobial efficacy than limonene against all microorganisms. The compounds demonstrated potent antimicrobial activity against bacteria (12.0 ± 1.7-33.1 ± 2.1 mm), yeasts (15.87 ± 0.81-24.5 ± 0.8 mm), and mycobacteria (8.5 ± 0.5-18.4 ± 2.1 mm). These findings were supported by low MIC and MBC/MFC (8-128 μg/mL), whereas MBC/MIC and MFC/MIC ratios (< 4) confirmed their bactericidal and fungicidal effect. Thymol also exhibited higher antimicrobial effect than the reference antibiotics (kanamycin, rifampicin, fluconazole, and chloramphenicol) against the tested microorganisms Moreover, in silico data showed that these compounds satisfy the main standards for drug-like molecules, with simulations pointing to good oral absorption, an acceptable safety profile, and stable binding to key enzymes in the studied microorganisms, which supports their antibacterial potential. Overall, these combined experimental and computational results point to thymol and limonene as promising natural antimicrobial agents.