Effect of Mao (Antidesma thwaitesianum) residue extract on bacterial resistance against Aeromonas hydrophila and Streptococcus agalactiae in Nile Tilapia

This study investigated the inhibitory effects of Mao (Antidesma thwaitesianum Müll. Arg.) residue extract against Aeromonas hydrophila and Streptococcus agalactiae in Nile tilapia. A. thwaitesianum is a tropical plant indigenous to Southeast Asia, recognized for its abundance of bioactive compounds such as flavonoids and tannins. Mao residue was extracted by water, 50% ethanol, or 95% ethanol. Antibacterial efficacy was assessed by the disc diffusion method, while the minimum inhibitory concentration and minimum bactericidal concentration were determined using the broth dilution method. In addition, qualitative phytochemical analysis of the crude extracts was conducted. The extracts at different concentrations were then supplemented into fish feed to evaluate their antibacterial resistance. The findings revealed that Mao residue extracted with 95% ethanol exhibited the strongest growth inhibition against both pathogens. The phytochemical analysis of extract revealed the presence of various secondary metabolites, including flavonoids, coumarins, alkaloids, saponins, tannins, and glycosides. In the feeding trial, Nile tilapia were fed commercial pellet feed supplemented with Mao extract at concentrations of 0%, 0.1%, 0.5%, and 1%. No statistically significant differences (p > 0.05) were observed among treatment groups in terms of growth performance, feed conversion ratio, or survival rate. However, the bacterial challenge test revealed that fish fed diets supplemented with 0.5% Mao extract exhibited the highest resistance to both A. hydrophila and S. agalactiae. In conclusion, this study suggests that dietary supplementation with 0.5% Mao residue extract possesses antibacterial potential against A. hydrophila and S. agalactiae.