Antimicrobial activity of endophytic fungi associated with Orchidaceae in Brazil

The purpose of this study was to examine antimicrobial activity of endophytic fungi isolated from the leaves, stems, and roots of 54 species of Orchidaceae collected in a Brazilian tropical ecosystem. In total, 382 filamentous fungi and 13 yeast isolates were obtained and cultured to examine the production of crude extracts. Thirty-three percent of the isolates displayed antimicrobial activity against at least one target microorganism. The multivariate statistical analyses conducted indicate that the extracts of endophytic fungi isolated from leaves of terrestrial orchids in semideciduous forest were more active against Escherichia coli, whereas extracts of endophytic fungi from roots of rupicolous orchids collected in rock fields were more active against Candida krusei and Candida albicans. Among the fungi that were screened in the study, 22 isolates held their antimicrobial activities after replication and were therefore selected for assessment of the minimum inhibitory concentration (MIC), which ranged from 62.5 to 250 mu g/mL and 7.8 to 250 mu g/mL against bacteria and fungi, respectively. One isolate of Alternaria sp. and one isolate of Fusarium oxysporum presented the strongest antibacterial activity. Three Fusarium isolates, Epicoccum nigrum, and Sclerostagonospora opuntiae showed the greatest MIC values against the pathogenic yeasts. This study is the first survey investigating the bioactive potential of endophytic fungi associated with tropical Orchidaceae species present in Brazilian ecosystems.