Inhibitory Activity of Lactic Acid Bacteria Isolated From Tilapia Gut Against Streptococcus Agalactiae

Tilapia culture offers cheap high-quality protein for the human population demand. However, with intensification, the cultured tilapia become threatened by Streptococcus infection, and antibiotic resistance emergence in aquaculture. Therefore, probiotics were investigated to be used as an alternative for antibiotics to treat Streptococcus infections. In the current study, probiotic lactic acid bacteria count ranged from 5.67 to 5.78 log10 CFU/g of tilapia gut microflora. The conventional biochemical tests were carried out for the lactic acid bacteria isolates identification. Only seven native isolates which exhibited inhibitory properties against Streptococcus agalactiae with an inhibition zone 26-50 mm in diameter were selected for characterization. All probiotic isolates were negative for hemolysis and produced both amylase and lipase enzymes. The selected strains tolerated the fish's gastrointestinal acidic and bile conditions. The promising features of the isolated strains indicate that probiotic bacteria of aquatic origin can be considered a safe alternative for pathogen control.