Properties of Enterococcus faecalis, a new probiotic bacterium isolated from the intestine of snakehead fish (Channa striatus Bloch)

The present study aimed to isolate and characterize the lactic acid bacteria (LAB) from the intestine of snakehead (Channa striatus) fingerling to be used as a new probiotic in aquaculture. The total colony count of bacteria in the fish intestine was 2.1 × 106 cfu/g. Five LAB were isolated from the intestine of twenty fish and one of these isolates, LAB-4 was identified as Enterococcus faecalis by conventional and molecular techniques. Probiotic properties showed that this LAB could grow from pH 3 to 8, but the best growth was observed at pH 7. E. faecalis grew at 0.15 and 0.3% bile salt concentrations, from 15to 45°C and at 4% NaCl‎ in de Man Rogosa and Sharp (MRS) broth. This bacterium showed in vitro inhibitory activity against three fish pathogens viz., Aeromonas hydrophila, Pseudomonas aeruginosa and Shewanella putrefaciens. Antibiotic sensitivity tests indicated that E. faecalis was resistant instantly to: streptomycin, gentamycin and kanamycin, intermediate to tetracycline, and sensitive to chloramphenicol, amoxicillin and ampicillin antibiotics. Moreover, significantly (P<0.05) improved survival of fish was observed when fed with E. faecalis-fortified diet in an in vivo challenge test using A. hydrophila. Based on the results, it can be concluded that E. faecalis is a promising probiotic for snakehead fish against pathogenic infestation.