Helvolic acid, an antibacterial nortriterpenoid from a fungal endophyte,<i>Xylaria</i>sp. of orchid<i>Anoectochilus setaceus</i>endemic to Sri Lanka

An endophytic fungus was isolated from surface sterilized leaf segments of <i>Anoectochilus setaceus,</i> an orchid endemic to Sri Lanka, and was identified as <i>Xylaria</i> sp. by morphological characters and DNA sequencing. Bioassay-guided chromatographic fractionation of the organic extract of a laboratory culture of this fungus led to the isolation of the known antibacterial helvolic acid. Helvolic acid was active against the Gram-positive bacteria, <i>Bacillus subtilis</i> [minimal inhibitory concentrations (MIC), 2 μg mL^-1] and methicillin-resistant <i>Staphylococcus aureus</i> (MIC, 4 μg mL^-1).