In vitro assessment on intestinal microflora from commonly farmed fishes for control of the fish pathogen Edwardsiella tarda

This study was aimed to evaluate the microflora isolated from the intestines of tilapia (Oreochromis niloticus), freshwater catfish (Clarias batrachus), snakehead (Ophicephalus striatus), snakeskin gourami (Trichogaster pectoralis), climbing perch (Anabas testudineus), and river catfish (Pangasius pangasius) for their potential probiotic development. Isolates were initially screened for their inhibitory effect against one of the most common fish pathogens, Edwardsiella tarda. Positive antagonists were subsequently tested for hemolytic activity, antibiotic susceptibility, and production of bacteriocin-like inhibitory substances (BLISs). Our results revealed 55 of the 405 isolates tested showed inhibitory effects towards the pathogen. Forty isolates were gamma-hemolytic bacteria. Only 7 isolates were nonresistant to tested antibiotics. They were identified as Lactococcus lactis based on 16S rRNA characterization. Our BLIS data suggest that L. lactis subsp. lactis CF4MRS at the cell density of 106 cfu/mL could be effectively used to control E. tarda.