In Vitro Evaluation of Probiotic Properties of Lactic Acid Bacteria from the Gut of Labeo rohita and Catla catla.

We report the evaluation of probiotic properties of potent lactic acid bacteria (LAB) from the gut of freshwater fishes, Labeo rohita and Catla catla, for eventually developing probiotic strains for the prevention of bacterial infections in aquaculture and food preservation. Five different LAB strains were isolated and characterized for their probiotic properties. Based on physiological, morphological and biochemical characteristics, three isolates from Labeo rohita and two from Catla catla were identified as putative probiotics and were denoted as LR11, LR14 and LR16 and CC3 and CC4, respectively. Isolates CC3 and CC4 were acid (pH 2.5) and bile salt (0.3% oxygall) tolerant and exhibited strong antibacterial activities against all pathogens including Aeromonas hydrophila. In addition, all LAB isolates were susceptible to tested antibiotics, except CC3 and CC4 which were vancomycin resistant. Furthermore, the isolates CC3 and CC4 showed significantly higher in vitro cell surface properties, i.e., hydrophobicity, auto- and co-aggregation. Biochemical tests, PCR detection and 16S rRNA sequence analysis established that LR11, LR14, LR16, CC3 and CC4 are Enterococcus avium TSU11, Enterococcus pseudoavium TSU14, Enterococcus raffinosus TSU16, Lactobacillus gasseri TSU3 and Lactobacillus animalis TSU4, respectively. Studies revealed that, Lactobacillus gasseri TSU3 and Lactobacillus animalis TSU4 are ideal probiotic candidates for its use in aquaculture and require further exploratory in vivo evaluation and safety studies.