Antibacterial activity of Streptomyces spp. against Aeromonas hydrophila causing hemorrhagic disease in intensively cultured pangasius catfish

Antibiotic-resistant bacteria are becoming more common due to the overuse of antibiotics in aquaculture. Alternative antibiotic solutions are fascinating and under the consideration in many countries. This study's objective was to isolate and identify certain actinomycete isolates with inhibitory action against the hemorrhagic disease-causing Aeromonas hydrophila in intensively cultivated catfish. This investigation isolated ten actinomycete isolates from sediment and water samples of catfish ponds in Vinh Long province. Using the diffusion well method, the study identified all isolates with antogonisttic activity against A. hydrophila. In particular, two isolates, BCA1.2 and BCA1.5, presented the highest inhibitory activity with inhibitory diameter zones of 11±1.0 mm and 10±1.0 mm, respectively. Two actinomycete isolates, BCA1.2 and BCA1.5, had their growth affected by pH, temperature, and NaCl. The findings revealed that two of these isolates showed optimum growth in a pH range of 7.0–8.0 and at 37°C. Two isolates, BCA1.2 and BCA1.5, survived well on medium containing a high salt concentration of NaCl ranging from 3% to 7% and were able to utilize different sources of carbon. They produced a wide range of hydrolytic extracellular enzymes, such as cellulase, amylase, protease, lipase, and chitinase. Isolates BCA1.2 and BCA1.5 were identified as Streptomyces based on morphological, cultural, physiological, and biochemical characteristics and 16S rRNA gene sequencing.