Potential utilization of Streptomyces extract as an antibacterial, anti-inflammatory and immune stimulant in Aeromonas hydrophila-infected Nile tilapia, Oreochromis niloticus

Frequent disease outbreaks in the aquaculture sector have increased with the widespread multiresistant bacterial strains as a result of overuse or misuse of antibiotics. Such diseases can lead to substantial economic losses and threaten the sustainability of aquaculture. Streptomycetes sp. is a genus of bacteria that produces numerous secondary metabolites with high potential as antimicrobial substances. Therefore, the present study aimed to evaluate the use of Streptomyces coeruleorubidus extract (SSM) on survival, immune, and inflammatory responses of Nile tilapia infected with Aeromonas hydrophlia. SSM was extracted from the bacterial media using ethyl acetate, then concentrated using a rotary evaporator, and injected into fish infected with or without A. hydrophlia. The results indicate that infected fish have a lower survival rate and experience low plasma levels of immune components such as IgM, lysozyme, and complement 3 levels. SSM treatment improved the survival rate of infected fish and stimulated immune responses in healthy or infected groups. The relative expression of pro-inflammatory cytokines was significantly increased by infection; meanwhile, anti-inflammatory cytokines were down-regulated. Treatment with SSM significantly regulated the expression of inflammatory cytokines. SSM revealed the potential to stimulate the immune response and improve the survival rate against pathogenic bacterial infection. It can be used and commercialized as an antibacterial agent and an alternative to antibiotics in aquaculture. Future studies could apply these metabolites in human applications; however, more studies are needed to study these metabolites and identify their composition.