An endophytic fungus was isolated from the leaves of the Chinese medicinal plant Taraxacum
mongolicum Hand.-Mazz. The phylogenetic and physiological characterization indicated that the isolate,
strain PG23, was Phoma sp. Culture filtrate of PG23 displayed antagonism against some pathogenic
bacteria owing to the existence of antibacterial compounds. The filtrate revealed in vitro strong
antimicrobial activity on the studied bacteria, confirmed by the inhibition zone diameter (24 h after
incubation) ranging from 24.2 to 40.0 mm depending on the microorganism being tested. The
antibacterial extract was fractionated and purified on silica gel chromatography. From the culture
extracts of PG23, a bioactive compound was isolated by bioactivity-guided fractionation and identified
as 2-hydroxy-6-methylbenzoic acid based on spectral analysis obtained from nuclear magnetic
resonance, infrared, and mass spectrometry. The results show that 2-hydroxy-6-methylbenzoic acid has
potential for poultry and aquatic product disease control.