Thesis (M.Sc.)--Chulalongkorn University, 2009

To investigate antimicrobial agents produced by endophytic fungi of Melaleuca cajuputi. Leaves and twigs of this plant collected from 4 provinces including Krabi, Nakhonsithammarat, Phatthalung and Trang were isolated using surface sterilization technique to afford 56 isolates of endophytic fungi. All fungal isolates were examined their antimicrobial metabolites using dual culture agar diffusion technique. It was found that there are twenty-six isolates produced antimicrobial metabolites and YES medium was an appropriate medium for production of the antimicrobial metabolites of those endophytic fungi. Isolate PTYL 6 was selected for the study because it produced metabolites against Escherichia coli ATCC 25923 and Candida albicans ATCC 10231 with inhibition zone of 20 and 21 mm, respectively. On basis of fungal morphology including microscopic and macroscopic features and molecular identification the fungal isolate PTYL6 was identified as Fusarium sp. This fungus was cultured in YEB and its antimicrobial metabolites were investigated. The EtOAc extract of mycelia was isolated to give a new compounds, 6-benzyl-3- isopropyl-1-methylpiperazine-2,5,dione and a known compound ergosterol while uracil was obtained from broth EtOAc and MeOH extract. Antimicrobial activities of two compounds were determined by the minimum inhibitory concentration (MIC) method using streptomycin and ketoconazole as positive control. The results showed that 6-benzyl-3-isopropyl-1-methylpiperazine-2,5-dione exhibited antimicrobial activity against Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, Candida albicans ATCC 10231, Staphylococcus aureus ATCC 25923 and Pseudomonus aeruginosa ATCC 27853 with MIC values of 1.96, 62.5 and 31.25 μg/ml, respectively, and ergosterol exhibited antimicrobial activity against Bacillus subtilis ATCC 6633 and Escherichia coli ATCC 25922 with MIC values of 250 and 250 μg/ml, respectively.