Screening and isolation of antibacterial activities of the fermentative extracts of freshwater fungi from Yunnan Province, China

The EtOAc extracts of cultural filtrates of 30 freshwater fungi were assayed for the in vitro antibacterial activity against Bacillus cereus YMF 3.19, Brevibacillus laterosporus YMF 3.08, Escherichia coli YMF 3.16, Staphylococcus aureus YMF 3.17 using the disc diffusion method. A total of 14 fungal strains displayed active against all of the bacteria tested and the strongest antibacterial activity was recorded in Camposporium quercicola YMF1.01300 isolate. Extraction of fermentation broth of C. quercicola YMF1.01300 and various separation and purification steps led to isolation of three pure active molecules. The chemical structures of these three compounds, a new diphenyl ether, named as quercilolin (compound 1), as well as two previously known compounds, tenellic acid A (compound 2), and 2',4'-dihydroxyacetophenone (compound 3), were established by analysis of NMR and MS data, and by comparison with reference data from the literature. These results indicate that some freshwater fungi could be a potential source of antibacterial agents.