The study was endeavoring to investigate in vitro as well as in vivo antibacterial and probiotic potential of Sphingomonas sp. AsCh-P3 (MF543123) and Bacillus aerius AsCh-A7 (MF543123) against fish pathogen Pseudomonas fluorescens. Antagonism by cross streak was observed in ten isolates out of total twenty. Six isolates showed better inhibition by well as well as disk diffusion methods with maximum growth inhibition zones i.e., 15 and 17 mm by Sphingomonas sp. AsCh-P3 and Bacillus aerius AsCh-A7 respectively. Six probiotic bacterial isolates of known enumeration (C.F.U.ml-1) showed growth antagonism for the fish pathogen with inocula comprising of less number of C.F.U.ml-1. Highest survival rates i-e 63.5 and 70.17% were expressed by Sphingomonas sp.AsCh-P3 and B. aerius AsCh-A7 respectively by mixing in formulated fish feed, drying and storing in refrigerator. Mortalitiesof Labeo rohita fingerlings challenged to P. fluorescens intraperitoneally appeared in a dose dependent manner with symptoms like hemorrhage, swelling of the belly and anus, scale damage etc. The pathogen challenged fish were administered with Sphingomonas sp.AsCh-P3 (group-G1) and B. aerius AsCh-A7 (group-G2) treated feed in different experimental set ups. Highest Relative Percent Survival (80-90%) was recorded for fish receiving probiotic feed prior and after injection (G1b, G2b). Provision of probiotics was evident to alleviate pathogen virulence in fish. The emerging multi-drug resistance and related side effects of conventional therapies have caused researchers to explore alternate strategies, such as probiotics employment for disease control in aquaculture.
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