Antimicrobial activities and phytochemical screening of endophytic fungi isolated from Cymbidium and Dendrobium orchids

This study reports the isolation of fungal endophytes from common orchids in Malaysia (Cymbidium and Dendrobium sp.), their antimicrobial activities and phytochemical constituents. Culturable fungal endophytes were sampled from surface-sterilized root tissues of Cymbidium and Dendrobium orchids, then identified via molecular approaches. To establish their antibacterial and antifungal activities, the identified fungal endophytes were tested by the agar well diffusion assay and dual culture technique, respectively. Results revealed a total of 59 fungal endophytes were isolated, and they were represented in eight different genera (Fusarium, Nigrospora, Lasiodiplodia, Exserohilum, Curvularia, Buergenerula, Trichoderma and Daldinia). Fusarium was the most dominant genus among the pool of isolates, with high isolation frequencies of 62.7% (37 isolates). Rare genera such as Buergenerula and Exserohilum were also discovered at lower frequencies (3.33%, 1 isolate each). Among the 59 isolates, 8 isolates (13.56%) demonstrated antibacterial activities (5.67 ± 0.58 to 25 ± 0.00 mm) against all 4 pathogens tested (Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa). All endophytic isolates were, however, capable of inhibiting the growth of at least one pathogenic fungus (Ganoderma boninense, Pythium ultimum, Fusarium solani, Candida albicans) (1.16 to 91.86% inhibition). Prominent antimicrobial activities were displayed by Fusarium incarnatum (C4) and Trichoderma asperellum (D7). Phytochemical analysis of extracts from these endophytes revealed that antimicrobial activities may be attributed to constituents like alkaloids, flavonoids, phenols, saponins, tannins and terpenoids. These results highlighted the potential of fungal endophytes from Orchidaceae as an alternative source for antimicrobial agents.