Staphylococcus aureus, Bacillus subtilis and Escherichia coli induced copious production of antibiotics in an overnight co-culture with three soil fungi
Keywords:
Co-cultivation, co-culture, soil fungi, bacteria, antibiotics, antimicrobial production, fermentationAbstract
Background: There is need for the development of new antibiotics to combat new resistant strains of pathogens. Currently, majority of the antibiotics in use were derived directly or indirectly from soil organisms because of the oligotrophic condition of the soil which lead to competition and production of antibiotics. Co-cultivation has been used to mimic this condition and the result is promising.
Objectives: To study the effect of co-culture in the production of antibiotic by 3 soil fungi.
Method: Nine fungal strains were isolated from soil sample using soil dilution method. Their antibiotic production potentials were evaluated using agar overlay method. Four isolates with large inhibition zone diameters against some bacteria were fermented in the same medium. The medium was extracted with ethyl acetate after 21 days and the extract tested for antibacterial activities against the same bacteria used earlier. The isolates that showed high potential for antibacterial activities were identified through a series of molecular methods: DNA isolation, PCR amplification, sequencing of the ITS region and nucleotide sequence blasting. Their fermentation extracts were subjected to analytical High Performance Liquid Chromatography (HPLC). The chromatographic peaks were identified by dereplication.
Result: Four isolates (labelled FG2, FG4, FG8 and FG9) had profound antimicrobial activity. Significant differences in the inhibitory activity were however observed between the pure isolates and their fermentation extract as results of inhibition zones in the fermentation extracts were 1-3 mm compared to the overlay method where the inhibition zone diameters ranged from 17-26 mm. The HPLC analysis revealed a diketopiperazine, 6-cyclo-(S-Pro-R-Leu) through dereplication. Diketopiperazines are known to have antibacterial, antifungal and anticancer properties and could have contributed to the observed antibacterial activity.
Conclusion: The co-cultivation of bacteria and soil fungi which mimicked the natural environment led to the copious production of antibiotics in the overlay experiment
