Antimicrobial potential of medicinal plants extracts against human pathogens

Background The surge of antimicrobial resistance makes it necessary to look for new sources of drugs; medicinal plants still form a supplier of bioactive secondary metabolites for the future. Objectives: The goal of the study was to test the ethnic selected medicinal plants for in vitro activity against a specific group of human pathogens, assess the strength (MIC/MBC), analyse the phytochemistry, examine mechanisms of action and interactions, conduct preliminary toxicity testing on mammalian cells to prioritize the leads for further development. Methods: The polarity series (hexane, ethyl acetate, 70% ethanol, aqueous; hydrodistillation for essential oils) was used to extract eight taxa, which were then subjected to agar diffusion and CLSI-guided broth microdilution (resazurin confirmation) screening. Phytochemical characterization included qualitative tests, total phenolic/flavonoid quantification (TPC/TFC), TLC, HPLC–DAD, and GC–MS. Mechanistic assays included membrane integrity, antibiofilm and quorum-sensing inhibition, time–kill kinetics, and checkerboard synergy with ciprofloxacin. Cytotoxicity (HepG2) determined CC₅₀ and selectivity indices (SI = CC₅₀/MIC). Results: Aromatic, phenolic-molecule-rich extracts—Thymus vulgaris and Origanum vulgare—proved to be the strongest and most reliable antimicrobial agents (zones over 25 mm; MIC₅₀≈31.25 µg/mL; geometric mean MICs ≈ 45–50 µg/mL), they were active in a way that disrupted membranes (leakage of ~ 68–72% at 1× MIC), Diminution of antibacterial biofilm activity was substantial (~ 73–78% at 100 µg/mL), rapid bactericidal kinetics (≥ 3 log₁₀ reduction at 24 h) and synergistic interactions with ciprofloxacin (FICI ≈ 0.42–0.45). Terminalia chebula was the next to be tested with moderate potency (MIC₅₀≈62.5 µg/mL). Very strong positive relationship was noticed between TPC and the antimicrobial power (r ≈ + 0.74 vs zone; r ≈ − 0.71 vs MIC, p < 0.01). In safety profiling, the winning ones were Thymus and Origanum (HepG2 CC₅₀≈1,400–1,500 µg/mL; SI ≈ 28–33). Conclusion: Ethnobotanical selection along with standardized assays pointed out Thymus and Origanum as high-priority leads for bioassay-guided isolation and preclinical evaluation; further fractionation, pharmacokinetics and in vivo toxicity/efficacy studies are suggested.