Antibacterial Activities of Endophytic Fungi Isolated from Mentha cordifolia Leaves and Their Volatile Constituents

Abstract

A total of 17 endophytic fungal isolates were obtained from the leaves of Mentha cordifolia Opiz (Lamiaceae). Seven isolates were identified to the level of genus by using taxonomically relevant morphological traits. Colletotrichum and Phomopsis species were dominant among these strains. All strains were separated from M. cordifolia leaf for the first time. The ethyl acetate extracts of all endophytic fungi were tested for antibacterial activity against Salmonella typhimurium TISTR1166 and Pseudomonas aeruginosa TISTR781. Most endophytes exhibited antibacterial activity. Ustilago sp. MFLUCC15-1024 presented the highest inhibition zone diameter with a MIC of 31.25 μg/mL against the tested pathogens. The chemical composition of the ethyl acetate extract of this strain was investigated using gas chromatography-mass spectrometry. Twenty-one components were identified. 2-Phenylethanol (38.7%), E-ligustilide (12.4%), α-eudesmol (10.2%), β-vetivone (4.6%), β-ylangene (3.7%) and verbanol (3.4%) were the major components of the extract. The strong antibacterial activity of Ustilago sp. MFLUCC15-1024 ethyl acetate extract may be attributed to the presence of a high concentration of bioactive compounds including phenyl ethyl alcohol, E-ligustilide and α-eudesmol. The results indicate that there is high diversity of endophytic fungi in M. cordifolia leaf, and that Ustilago sp. MFLUCC15-1024 strain could be an excellent resource of natural antibacterial compounds.