Phytochemical Profiling and In Vitro Antimicrobial Potential of Hypericum decaisneanum Coss. Aerial Parts Endemic to Bani Waleed, Libya

Abstract

The escalating global threat of antimicrobial resistance (AMR) has necessitated the exploration of novel bioactive compounds from medicinal plants. This study was conducted to evaluate the in vitro antimicrobial efficacy and preliminary phytochemical profile of Hypericum decaisneanum Coss., a species endemic to the Bani Waleed region of Libya. Aerial parts of the plant were collected during the flowering season in May 2023. These materials were shade-dried and successively extracted using three solvents of varying polarity: methanol, ethanol, and distilled water via a Soxhlet apparatus. The antimicrobial activity was assessed against a diverse panel of microorganisms, including Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae), and the fungal strain Candida albicans using the agar well diffusion assay. Quantitative assessments were performed to determine the minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) through the broth microdilution method. Results indicated that the methanolic extract exhibited the most potent and broad-spectrum antimicrobial activity. It demonstrated significant inhibition zones against all tested strains, particularly against S. aureus (21.3 ± 0.6 mm) and C. albicans (19.5 ± 0.7 mm). The MIC values for the methanolic extract ranged from 0.312 mg/mL to 2.5 mg/mL, with the lowest MIC observed against S. aureus. The MBC/MFC values were generally equal to or twice the MIC values, suggesting a primarily cidal mode of action. In contrast, the ethanolic extract showed moderate activity, while the aqueous extract was largely ineffective. Phytochemical screening of the methanolic extract revealed a rich presence of tannins, flavonoids, terpenoids, and anthraquinones. Quantitative analysis confirmed high levels of total phenolic content (185.4 ± 5.2 mg GAE/g) and total flavonoid content (112.6 ± 4.1 mg QE/g). These findings validate the potential of H. decaisneanum as a source of natural antimicrobial agents and warrant further bioassay-guided fractionation to isolate specific active principles