Probiotic Antagonism of Sphingomonas sp. against Vibrio anguillarum Exposed Labeo rohita Fingerlings

Abstract

Antagonistic properties of Sphingomonas sp. AsCh-P3 against fish pathogen V. anguillarum was investigated in vitro and in vivo assays. Out of twenty probiotic isolates, nine expressed antagonistic activity by cross streak and six gave prominent results by disc and well diffusion methods. Maximum growth inhibition zone (15 mm) was observed by Sphingomonas sp. AsCh-P3. Cross streaks of six isolates of known C.F.U./ml across different concentrations of pathogen indicated profound growth inhibition by low concentration. The six bacterial isolates were mixed in fish feed, dried and stored in refrigerator upto 4 days. Sphingomonas sp. AsCh-P3 showed 63.5% survival in dried feed under the storage condition and grew best with 30% inoculum size in 20 % fish feed extract. The Labeo rohita fingerlings were exposed to V. anguillarum intraperitoneally. Fish mortalities appeared in a dose dependant manner. Pathogen exposed fishes were provided with Sphingomonas sp. AsCh-P3 treated feed in different experimental groups as G1-soon after, G2- prior and after and G3- prior challenge. Percent mortalities of 33.33, 16.66 and 23.33 and RPS values of 16.67, 58.35 and 41.67 were recorded for G1, G2, and G3, respectively. Probiotic loads reduced the pathogens virulence in dose responsive manners.