Potential probiotic and health fostering effect of host gut-derived Enterococcus faecalis on freshwater prawn, Macrobrachium rosenbergii

Abstract The present study investigated the potential probiotic effect of Enterococcus faecalis against a pathogenic microorganism, Vibrio harveyi occurring in the giant freshwater prawn (Macrobrachium rosenbergii). V. harveyi was isolated from the intestine of M. rosenbergii through biochemical tests and PCR-based molecular assays. An in-vitro challenge was conducted by mixing isolated probiotic (5.12 log CFU/g) and V. harveyi (3.09 log CFU/g). Feeds incorporated with E. faecalis (9.02 log CFU/g) were applied to the treatment group during in vivo test in the aquarium and earthen pond (70 m2, 1 m depth). Pathogenic bacteria were found to be reduced after 8 h (from 5.02 to 3.62 log CFU/g) and 60 days (from 5.44 to 2.15 log CFU/g) of probiotic administration in the in vitro and in vivo test, respectively. The E. faecalis mixed feed also showed higher weight gain (WG%, 481.22% ± 17.71%; SGR%, 2.93% ± 0.18%) and digestive enzymes activities (amylase, 1.26 ± 0.08 unit/mg; protease, 2.78 ± 0.02 unit/mg) compared to control group (WG%, 371.31% ± 13.35%; SGR%, 2.30% ± 0.32%; amylase, 0.7 ± 0.03 unit/mg; protease, 1.82 ± 0.02 unit/mg). Furthermore, the probiotic also improved the immune response by augmenting NGH (from 73.33% ± 0.23% to 74.63% ± 0.11%) and SGH (from 22.24% ± 0.06% to 23.13% ± 0.08%) in the treatment group. Therefore, E. faecalis could be recommended to use against bacterial infections of the M. rosenbergii.