Antimicrobial and Cytotoxic Potential of Endophytic Aspergillus versicolor Isolate from the Medicinal Plant Plectranthus amboinicus.

Endophytic fungi are non-pathogenic organisms that colonise healthy plant tissues asymptomatically. Endophytes derived from medicinal plants are sources for identifying natural products and bioactive compounds with potential uses for industry, medicine, agriculture, and related sectors. In the present study, ethyl acetate crude extracts of four endophytic fungal isolates (CALF1, CALF4, and CASF1) from the medicinal plant Plectranthus amboinicus showed potent antimicrobial activity against the test pathogenic bacteria Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis using disc diffusion assays. A colorimetric microdilution assay to detect the minimum inhibitory concentration (MIC) revealed that the extracellular extract (ECE) of CASF1 isolate had the lowest MIC values against the test pathogenic bacteria (0.19-6.25 mg/ml) compared to other CALF1 and CALF4. Cytotoxic activity of CASF1-ECE against the drug-resistant KB.CHR.8-5 cancer cell line tested by the MTT assay showed complete cell death at a concentration of 220 μg/mL and the half-maximum inhibitory concentration (IC₅₀) was determined to be 77.9 ± 09 μg/mL. GC-MS analysis showed hexadecanoic acid, 2-hydroxy-1-(hydroxymethyl) ethyl ester, as the dominant compound among the bioactive compounds identified in the EXE of CASF1 isolate, with the highest peak in the GC chromatogram, indicating its role in the antimicrobial and cytotoxic activity of CASF1. Molecular identification of CASF1 using 18S rRNA sequencing and BLAST analysis detected CASF1 as an isolate of Aspergillus versicolor with 100% sequence identity.