Antibacterial and Immunostimulatory Effects of Raziz Date Palm Pits in Streptococcus agalactiae-Infected Red Hybrid Tilapia.

Aquaculture is an important food sector, which involves the commercial production of fish for consumption. Tilapias (Oreochromis sp.) are hardy and are one of the most commonly produced fishes in the aquaculture industry. Disease outbreaks caused by Streptococcus agalactiae, however, widely affect tilapia farms, resulting in high mortality. Consequently, this may lead to the misuse of antibiotics for the prevention of disease or overuse of antibiotics when used for the treatment of fishes, contributing to antibiotic resistance. In this study, date palm pits, a waste product from the date palm industry, were tested for potential antibacterial activity against S. agalactiae and for their ability to act as an immune enhancer in vitro through the use of the head kidney and serum from healthy adult tilapias. An in vivo study was performed by dividing tilapias into two groups, consisting of infected S. agalactiae and uninfected S. agalactiae. Each group consisted of extract-fed and distilled-water-fed tilapia. Then, the serum, spleen and head kidney were isolated from both groups and tested for their respiratory burst, lysozyme and myeloperoxidase activities. The results from this study indicate that the Raziz methanol extract at a concentration of 1 g/mL inhibited the growth of S. agalactiae, and concentrations of 10 mg/mL, 2 mg/mL and 0.016 mg/mL displayed the highest respiratory burst, lysozyme and myeloperoxidase activities, respectively, in vitro. In the infected group, extract-fed tilapias showed a significant effect on respiratory burst activity and lysozyme activity compared to the distilled-water-fed tilapias, while no significant activity was observed in the uninfected group. In conclusion, the Raziz methanol extract has promising potential to act as an antibacterial agent, and it enhanced the innate immune function during active infection of S. agalactiae.