Nguyen Van Thanh, Trinh Thi Trang, Nguyen Thanh Hai

Aquaculture is rapidly expanding in area and in intensity; however, there are serious problems caused by bacterial infection. The use of antibiotics is not sufficient to mitigate the outbreaks due to increase in antibiotic resistance. Therefore, to overcome the challenges of antibiotic resistance, antimicrobial compounds with a new mechanistic approach should be urgently sought. The aim of this study was to isolate and evaluate the antimicrobial activity of endophytic actinobacteria from Horsetail plant (Equisetum diffusum D. Don) against two pathogenic bacterial species Aeromonas hydrophila GL14 and A. veronii HY15 that cause severe disease on common carp and catfish. The results showed that 9/32 (28.2%) endophytic actinobacteria isolates could inhibit at least one target pathogenic bacteria. Three isolates TB13, TB21 and TB17 showed the highest antibacterial response with minimum inhibitory concentration (MIC) ranging from 93.3 to 300 µl/mL. Amongst these, the lowest value was observed in TB21 and MTR622 without significant difference. When combining three individual actinobacteria mentioned above for fractional inhibitory concentration (FIC) test, the synergistic effect was found for the pair of TB13-TB17 against two tested pathogenic bacteria chosen with ∑FIC ≤0.5. The combination of two actinobacteria TB13 and TB17 improved bacterial inhibitory effect at least 4 times as compared with individual treatment. The results are motivating enough to conduct further studies on the use of endophytic actinobacteria for treating pathogenic bacteria in aquatic animals.

Key words: May Chang, actinobacteria, Aeromonas, common carp, tilapia.

Some picture in the study: