The antibacterial activity of twelve different wood-decay fungal isolated in Southern Vietnam was investigated to find out the new potential antibiotics produced by macro fungi. The antibacterial activity of the collected fungal isolates was tested by three screening methods against seven different strains of bacteria: Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Vibrio parahaemolyticus, Vibrio cholerae, and Salmonella typhi. The screening test were performed at first with mycelium grew on surface of agar medium similar to a disc diffusion test, next by an extracellular metabolite test by flood-plate method, and finally with an intracellular metabolite test using grounded mycelium fluid. To determine the activity of metabolites produced in the mycelium, the fungal isolates were grown on culture substrates to promote mycelium formation. Antibacterial activity of the selected fungi was confirmed by disc diffusion method using crude extract of the mycelium harvested from the substrate cultures. Four fungal species identified with strong antibacterial compounds produced by their mycelium including Pycnoporus sanguineus, Flavodon flavus, Fomitopsis ostreiformis and Meripilus giganteus. Crude extract of Pycnoporus sanguineus showed the strongest antibacterial activity, with 7/7 bacterial strains inhibited. Fomitopsis ostreiformis antibacterial activity was recognized with the ability to inhibit 6/7 bacterial strains. Flavodon flavus and Meripilus giganteus showed weaker activity than other two species, with only 4/7 strains inhibited. The fungal isolates identified with antibacterial activity discovered in this study can be potential candidates for the new source of antibiotic to fight against new generations of antibiotic resistance bacteria in the future.

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This research demonstrated antibacterial activity of wood-decaying fungi to treat the aquaculture pathogenic bacterium, Vibrio parahaemolyticus (V. parahaemolyticus). Three wild wood-decaying fungi (WDF) collected in Southern Vietnam including Flavodon flavus (F. flavus), Physisporinus vitreis (P. vitreis), and Schizophyllum commune (S. commune) were tested to treat V. parahaemolyticus presented in aquaculture wastewater. Fungal adaptation to different salt concentrations at 0, 10, 15, 20, and 30‰ was tested for the assessment of application potential of these fungi in the aquaculture farming. Fungal mycelium could adapt differently to saline conditions. All three strains grew well at low salt concentration (0-10‰), but only F. flavus survived up to 20‰ NaCl. For the antibacterial ability toward V. parahaemolyticus, two experiments using mycelium culture broth and mycofiltration were performed. Results revealed that all the three species of WDF effectively inhibited V. parahaemolyticus. Thus, mycelium culture broth of P. vitreis, S. commune, and F. flavus could inhibit 98.7, 96.5 and 97.8% V. parahaemolyticus, respectively after 8 hours. Even higher inhibitory effects were observed in the mycofiltration experiment, the efficiency reached 100% for P. vitreis, and 98% for F. flavus and S. commune after 8 hours. The obtained results showed very good application potential of myco-remediation technique using WDF in the treatment of V. parahaemolyticus in aquaculture farming. Mycofilter can be used as a new approach for controlling aquaculture disease, specifically Vibrio sp. treatment based on the antibiotic capability of these WDF. The reduction in pH of the mycelium broth can illustrated for the acidification during the mycelium development and could link with the bactericide capacity of these WDF.

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