Characterization of a Probiotic Lactobacillus fermentum Isolated from Snakehead, Channa striatus, Stomach

This study sought to isolate and characterize lactic acid bacteria ( LAB ) from stomach of adult snakehead fish, Channa striatus , to be used as probiotics for freshwater fish. A total of 13 strains were isolated from the stomach of 10 fish, and 4 of these belonged to LAB . Strain LAB ‐3 showing highest in vitro growth inhibition of Aeromonas hydrophila in a disk diffusion test was identified as Lactobacillus fermentum by conventional and molecular techniques and evaluated in vitro through various tests. The bacterium could grow at pH 3–8; but the optimum growth was observed at pH 6. Moreover, LAB ‐3 grew at 0.15 and 0.3% bile salt concentrations, from 15 to 45 C, and at 4% NaCl . L . fermentum showed in vitro inhibitory activity against three fish pathogens, A. hydrophila , Pseudomonas aeruginosa , and Shewanella putrefaciens , tested by disk diffusion and well diffusion methods. Antibiotic sensitivity tests indicated that L . fermentum was resistant to streptomycin, gentamycin, and kanamycin, intermediate to tetracycline, but sensitive to chloramphenicol, amoxicillin, and ampicillin. Challenge test by using A . hydrophila showed that survival of snakehead was significantly ( P < 0.05) improved when 2 × 10 6 LAB ‐3/g was supplemented to the diet. Therefore, this study suggests that L . fermentum might be a promising probiotic in snakehead aquaculture .