Investigation of antibacterial activity and toxicity of extracts of Lumnitzera racemosa-derived endophytic fungi

Endophytic fungi are recognized as promising source of diverse bioactive compounds. In particular, mangrove-derived fungal endophytes are known to provide distinct microbial diversity capable of producing various pharmacologically active compounds, due to their exposure to various environmental stresses. This study investigated the antibacterial activity and toxicity of extracts of endophytic fungi isolated from mangrove Lumnitzera racemosa, collected in Bali, Indonesia. Following fungal isolation procedure, three endophytic fungal isolates, namely ER1, ER2 and ER3 were isolated from healthy tissue of stem and fruit of L. racemosa. Each isolated fungus was cultivated on rice media for 4 weeks, followed by extraction using ethyl acetate and solvent removal by vacuum rotary evaporator, yielding three extracts. Each ethyl acetate extract was partitioned between aquaeous methanol and n-hexane. All of the resulting methanol extracts were subjected to phytochemical analysis and tested for their antibacterial and toxicity. Antibacterial assay was performed with microdilution technique, whereas the toxicity was screened through brine shrimp lethality test (BSLT). Phytochemical analysis indicated the presence of alkaloids, terpenoids, triterpenoids, and polyphenols in each extract. When tested for their antibacterial activity against Staphylococcus aureus ATCC 25923, all of the tested extracts were found to be inactive up to the tested concentration of 1000 µg/mL. Albeit no activity was found in antibacterial assay, all of the tested extracts displayed toxic effect against brine shrimp with LC50 values ranging from 324.94 to 406.68 µg/mL. Many toxicity studies on natural products employing BSLT revealed positive correlations with their cytotoxicity against various solid tumor cell lines. Thus, result of this study implied all of the tested extracts merit further investigation of their cytotoxic activity towards cancer cell lines.