Antibacterial, Antifungal, and Cytotoxic Activity of Excoecaria agallocha Leaf Extract

Mangroves contain several bioactive compounds, some of which have been used for centuries as remedies for several ailments.

Foliar parts of Excoecaria agallocha were extracted in organic solvents and in water using a Soxhlet apparatus and evaluated for antimicrobial activity against nine type-culture pathogens, six clinical isolates, and two fungal pathogens with agar well diffusion assays. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth dilution and extracts further subjected to brine-shrimp cytotoxic assays using Artemia salina. Chemical constituents were analyzed with thin-layer chromatography (TLC), gas chromatography-mass spectroscopy (GC-MS), and Fourier-transform infrared spectroscopy (FT-IR).

Ethyl acetate extract displayed the broadest antimicrobial activity. Isolates of Staphylococcus aureus were found to be the most susceptible among the clinical and type-culture groups corresponding to inhibition zones: 17.3±1.1 and 23.5±1.3 mm in diameter, respectively. Anticandidal activity was found to be lower against Candida albicans and C. tropicalis (10.3±0.6 and 11.9±0.85 mm diameter). Also, this extract was found to be bactericidal for S. aureus and Micrococcus luteus (MBC:MIC ≤2). _C cytotoxic activity LD₅₀ was 521 µg/mL. On GC-MS, squalene [(6E, 10E, 4E, 18E)-2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene] was the major compound. Bioassay-guided (antibacterial) TLC revealed the presence of one major active fraction, F2, with an R value of 1.21. FT-IR analysis of this fraction also implied that it was squalene, which might have a functional role in the mechanism of chemical defense.