EFFECT OF PROBIOTICS ISOLATED FROM NILE TILAPIA (Oreochromis niloticus Linn.) ON GROWTH, INNATE IMMUNITY AND INHIBITION OF PATHOGENIC BACTERIA
Nile tilapia culture has been commonly infected with bacterial diseases, especially by streptococcosis. Drug applications are not recommended due to risk of bacterial resistance development and residual problem. Thus, the application of probiotics bacteria should be an excellent alternative method for the control of fish pathogenic bacteria. This paper reported the isolation and selection process of effective probiotics for the control of streptococcosis.
We investigated the characteristics of two potential probiotics, Bacillus amyloliquefaciens and B. pumilus, isolated from Nile tilapia (Oreochromis niloticus) intestine and identified by 16S rRNA PCR analysis sequencing. They were tested for inhibition activity with fish pathogenic bacteria, Streptococcus agalactiae and Aeromonas hydrophila, and specific protease activity (Table 1).
Both Bacillus could survive in pH 2-9 condition for 6 h and 2 h in 0.5 - 2.0% bile salt. For in vivo test, Nile tilpia were fed with diet containing these two Bacillus at 1×108, 3×108 and 5×108 CFU g-1for 60 d for 0.2 g tilapia and 30 d for 50 g tilapia. The average weight, average daily growth, specific growth rate and feed conversion ratio were not significantly different (P>0.05). The survival rate postchallenge of S. agalactiae and stress test were also not significant (P>0.05). Innate immune parameters including superoxide anion and complementary activity were not significantly different (P>0.05). However, lysozyme, phagocytic and respiratory burst activity of some probiotics diet groups were significantly higher than control (P<0.05) (Figure 1).