Isolation of putative probionts from the intestines of Indian major carps

Abstract

Probiotic strains were isolated from the intestines of 28 Indian major carps (Labeo rohita, Catla catla, Cirrhinus mrigala) cultured in sewage-fed ponds. Intestinal microflora were isolated, counted, and identified, and their in vitro antibacterial properties were determined. The double layer method revealed that four strains (SG1, SG2, SG3, SG4) elicited antagonism against the pathogen Pseudomonas fluorescens. Using cross streak and parallel streak methods, SG4 maximally inhibited the fish pathogens Pseudomonas fluorescens, Aeromonas hydrophila, and Edwardsiella tarda. Therefore, SG4 was chosen for further study as a probiont. SG4 was non-pathogenic to C. mrigala fingerlings, and adhered well to stainless steel, high density polyethylene, and glass plate substrates. Biochemical tests showed that SG4 was endospore-forming, aerobic, motile, rod-shaped Bacillus subtilis. However, since in vitro experiments can only give an indication of in vivo success, future research should include large-scale in vivo experiments.