Preliminary study on antibacterial activity of endophytes isolated from some Rafflesia species in Malaysia

Studies on endophytes are gaining interest because of the active compounds produced by these microorganisms. In this study, seven endophytes were isolated but only five were successfully subcultured, i.e. ARB 6a13(i), ARB 6a13(ii), ARB 12a9, Bud 1 and Bud 4 from Rafflesia cantleyi and R. azlanii. These endophytes were characterized as fungi using macroscopic and microscopic techniques but identification until generic level was not achieved. They were screened towards six pathogenic bacteria that consisted of two Gram positive bacteria and four Gram negative bacteria. In addition, these endophytes were also tested against three strains of bacteria isolated from soil. Only ARB 6a13(i) showed inhibition towards the growth of Pseudomonas aeruginosa. To understand when these active substances were produced, the life cycle of ARB 6a13(i) was studied by looking at its biomass pattern and antibacterial activity over eight days. Biomass of this endophyte increased exponentially starting from the third day and became constant from the sixth until the eighth day. Inhibition of bacterial growth started on the third day with the highest inhibition on the fifth and sixth day. ARB 6a13(i) cultured in Potato Dextrose Broth (PDB) showed a broader range of antibacterial activity than when cultured on Potato Dextrose Agar (PDA). The inhibition observed was against Pseudomonas aeruginosa, Bacillus subtilis and Salmonella typhi. The results of this study suggest that endophytic fungi produce active compounds that may have medicinal value. Further and more in-depth studies about these compounds may lead to the development of novel products beneficial to human kind