Streptomyces Extract Supplemented Heat-Killed Vaccine Treatment Effectively Suppress the Vibrio Anguillarum Infection in Tilapia (Oreochromis niloticus) Fish

This study was carried out to assess the effect of Streptomyces sp. VITMK3 derived cell-free supernatant on tilapia fish (Oreochromis niloticus) infected with Vibrio anguillarum. Streptomyces showed inhibitory activity against V. anguillarum was characterized by molecular taxonomy and chemotaxonomic methods. It was identified as Streptomyces species and was designated as Streptomyces sp.VITMK3. Oreochromis niloticus was divided into six experimental groups. Groups A and B served as the negative and positive control, respectively. Groups C and E were vaccinated with heat-killed and formalin-killed vaccines of V. anguillarum. Groups D and F were vaccinated with lyophilized cell-free supernatant of Streptomyces sp. VITMK3, along with the heat-killed and formalin-killed vaccines respectively. A booster dose was also given after 14 days. Following the treatment, all the groups, excluding the negative control, were infected with V. anguillarum by intraperitoneal injection. Groups D and F showed higher survival of 86.6% and 73.33%, respectively, when compared to groups C and E (59.9% and 53.55%). Hemorrhagic spots, tail, and fin rot were observed in positive control. These results suggest that the isolate could be used as a potential bacterial antagonist, probiotic, and immunostimulant to control V. anguillarum infection in Oreochromis niloticus.