Anti microbial activities of endophytic fungi isolated from selected Thai medicinal plants

The aim of the present study was to isolate endophytic fungi from Thai medicinal plants and screen for their antimicrobial activities. Fungi were isolated from surface sterilized leaves and limbs of plant specimens placed on water agar medium by hyphal tipping. A total of 252 morphologically distinct pure isolates of endophytic fungi, mostly mycelial sterilia, were obtained from 45 plant species. The fungi were cultivated on 5 different media including Czapek yeast autolysate agar, malt Czapek agar, malt extract agar, Saburaud's dextrose agar, and yeast extract sucrose agar. Dual-culture agar diffusion technique was used to determine the antimicrobial activities against Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Saccharomyces cerevisiae, and Trichophyton mentagrophytes. Antimicrobial activities against one or more test microorganisms were found in 190 fungal endophyte isolates (75.4%). Among these, 94 isolates (37.3%) were active against both bacterial and fungi while 47 isolates (18.7%) exhibited only antibacterial activities and 49 isolates (19.4%) showed only antifungal activities. Most of the isolates having antimicrobial activities were active against gram-positive bacteria and filamentous fungus. However, a considerable number of the fungal endophyte isolates were inhibitory to gram-negative bacteria E. coli and P. aeruginosa. Endophytic fungi possessing anti-Candida albicans activity were found at nearly at three times more frequent than those having anti-S. cerebisiae activity. Type and intensity of antimicrobial activities produced by endophytic fungi were dependent on the culture media used. Higher number of fungal endophytes isolates expressed their antimicrobial activities when they were grown on malt Czapek agar or malt extract agar than the other culture media. Endophytic fungi, especially those from medicinal plants, could be potential and attractive sources of new antimicrobial antibiotics