Isolation of Probiotic Strains from Fishes Cultured in Sewage-fed Ponds

Abstract

The research for the need of probiotics in aquaculture is increasing with the demand for environment friendly aquaculture. The present study aimed at to isolate probiotic strains from the gut of carps cultured in sewage-fed ponds. The fish gut was dissected longitudinally and the entire gut content was plated onto deMann Rogosa Sharp (MRS) Agar for allowing the Lactic Acid Bacteria (LAB) to manifest itself as white pinpoint colonies. The MRS Agar plates containing LAB were then over-layed with osft Tryptone Soya Agar (TSA) containing pathogenic Pseudomonas cells at 105 nos/ml. Those LAB which produced a clear inhibitory zone with a diameter more than 1 mm larger than that of the colony itself was judged to be a tentative probiotics strain. During the present study, four strains (SM1, SM2, ST1 and ST2) gave a clear inhibitory zone and were classified as tentative probiotic strains. The four tentative probiotic strains were further confirmed of its probiotic effect against three pathogenic strains of Pseudomonas, Aeromonas and Edwardsiella by antagonistic assay by cross streak method and among four only two strains SM2 and ST1 exhibited an inhibition of 2 mm and 1 mm, respectively against the three pathogenic test strains and confirmed their status as probiotic strains.