In vitro Suppression against Streptococcal Bacteria and Health-Promoting Effects of Probiotic Bacillus polyfermenticus in Tilapia (Oreochromis niloticus)

Abstract

In vitro antibacterial activity of Bacillus polyfermenticus (BP) against tilapia streptococcal pathogen was evaluated using the agar dilution method and co-incubation method. Both in vitro tests confirmed the inhibitory effect of B. polyfermenticus on the growth of Streptococcus agalactiae. The suppression of S. agalactiae was observed in the test system containing B. polyfermenticus and the inhibition was more evident in the system with high density of
B. polyfermenticus. Subsequently, feeding administration of BP was employed in tilapia broodstocks (12 months old) and fry (37.33 ± 1.37 mg body weight) to examine the effect of BP on health performance. Significantly higher amount of fertilized eggs was recorded in the tilapia broodstocks fed BP supplemented diet for 5 months as compared with the control groups (p < 0.05); however no significant differences were found in the survival of broodstocks between the treatment and control groups. The tilapia fry fed on BP diet for 28 days also displayed significantly improved feed conversion ratio, average daily weight gain and survival rate. The study demonstrated in vitro anti-streptococcal potency of B. polyfermenticus and the potential of BP dietary supplement in promoting tilapia health performance.