Screening for Antibacterial Activity of Fungal Isolates from Decaying Plant Material in Samal Island, Davao del Norte

Abstract

Plant litter in tropical rainforests harbor fungi that are potential sources of medically important antibiotics and agriculturally significant biocontrol agents. Decaying plant material were collected from 10 randomly selected tree species in the forest of Babak District, Samal Island, Davao del Norte. Fungi were isolated from the collected plant material by plating serial dilutions on Potato Dextrose Agar (PDA) and Malt Extract Agar (MEA). A total of 70 molds were isolated and screened for antibacterial activity against the Gram-positive human bacterial pathogens Enterococcus faecalis and Streptococcus pyogenes, as well as the Gram-negative plant bacterial pathogens Erwinia carotovora and Ralstonia solanacearum using the Disk Diffusion Method. None of the mold isolates produced zones of inhibition against E. faecalis and S. pyogenes, however, eight isolates were found to inhibit E. carotovora and R. solanacearum. The inability of the mold isolates to inhibit the human pathogens may be due to the antibiotics having inappropriate mode of action to target, or they may not have been produced in the amounts needed to effectively inhibit the two human pathogens. On the other hand, antibiosis may be due to the production of toxic metabolites that inhibited the growth of the plant pathogens. The eight mold isolates that exhibited antibacterial activity were identified as the Deuteromycetes Gliocladium sp., Aspergillus oryzae, Acremonium sp., Trichoderma viride, Geomyces sp., Fusarium sp., Cladosporium cladosporioides, and Scopulariopsis sp..