Chemical Characterization and Evaluation of Antimicrobial, Antioxidant, and Synergistic Activities of Teucrium polium L.: An Integrated Experimental and In Silico Approach.

Background/

Objectives

Teucrium polium L. is widely used in traditional medicine and has been proposed as a source of antimicrobial adjuvants in the context of antimicrobial resistance. Here, we characterized the essential oil (EO) and polar extracts of T. polium and evaluated their antioxidant activity, antimicrobial potency against clinical multidrug-resistant (MDR) isolates, and the interaction of the EO with conventional antibiotics using a chequerboard assay (FICI); further, we investigated in silico molecular interactions with some targets related to resistance. Methods/

Results

The EO, which was hydrodistilled and subsequently analyzed by GC-MS, is characterized by dominant limonene content (24.13%) and contents of oxygenated sesquiterpenes such as β-eudesmol (10.48%) and α-muurolol (8.10%). HPLC/UV-ESI-MS characterization of the extracts (decoction and Soxhlet) demonstrated that they were rich in polyphenolic compounds and flavonoids, which matched the standard phytochemical characteristics of this species. The extracts exhibited significant reducing capabilities, and the hydroethanolic extract exhibited the highest antioxidant activity (DPPH IC50 = 15.41 μg/mL; FRAP EC50 = 30.65 μg /mL), while the EO revealed at most moderate capacity in these tests. In antimicrobial assays, the EO inhibited fungi more effectively than the extracts (MIC of 1.17 mg/mL against Aspergillus niger; 4.69 mg/mL against Candida spp.), while antibacterial MICs for both the EO and extracts were generally high (up to 50 mg/mL). Combination testing nevertheless identified synergistic or additive effects of the EO with selected antibiotics, notably with ceftazidime against ESBL-producing Escherichia coli (FICI = 0.141) and Staphylococcus aureus (FICI = 0.039) and with amikacin against Klebsiella pneumoniae (FICI = 0.313); the EO-ceftriaxone pairing against ESBL E. coli was additive (FICI = 0.516). Docking simulations further supported these observations by showing the favorable predicted binding of oxygenated sesquiterpenes, most notably β-eudesmol and α-muurolol (up to -8.6 kcal/mol), to resistance-related targets such as RND efflux pumps, β-lactamases, and porins.

Conclusions

Taken together, the in vitro and in silico data suggest that T. polium could be explored as a natural antimicrobial option and as an adjuvant to enhance antibiotic activity against multidrug-resistant pathogens.