Isolation and Evaluation of Antibiotic Activity of Endophytic Actinobacteria on May Chang Tree (Litsea cubeba) against Pathogenic Bacteria Causing Diseases on Common Carp and Tilapia

Abstract

    Tilapia and common carp are two main cultured species with high annual production in freshwater aquaculture in northern Vietnam. However, there are serious problems caused by bacterial infection. The use of antibiotics is not sufficient to mitigate outbreaks of the diseases due to antibiotic resistance of the causal agents. Therefore, antimicrobial compounds are potential as a new approach to overcome the challenges of antibiotic resistance. The aim of this study is to isolate and evaluate antibiotic activity of endophytic actinobacteria from May Chang tree (Litsea cubeba) against three pathogenic bacterial species Aeromonas hydrophila GL14, Aeromonas caviae HD60 và S. agalactiae HY10. The results showed that 9/32 (28,2%) endophytic actinobacteria isolates could inhibit at least one target pathogenic bacteria. Three isolates MTR711, MTR622 and MTL121 showed the highest antibacterial response with minimium inhibitory concentration (MIC) ranged from 93,3 to 300,0 μl/mL, amongst these the lowest value is for MTR711 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 MTR711- MTR622 against three pathogenic bacteria chosen in this study with ΣFIC ≤ 0,5. The combination of two actinobacteria MTR711 and MTR622 improved bacterial inhibitory effect at least 4 times compared to individual treatment. The results are motivating enough to conduct further studies on use of endophytic actinobacteria for treating pathogenic bacteria in aquatic animals.