A probiotic Enterobacter sp. provides significant protection against Flavobacterium psychrophilum in rainbow trout (Oncorhynchus mykiss) after injection by two different routes

Abstract

To determine the potential for protection against Flavobacterium psychrophilum infection, a study was conducted where a probiotic, Enterobacter sp. strain C6-6, was delivered to rainbow trout, Oncorhynchus mykiss, via injection. Two separate studies were conducted. In a preliminary study groups of rainbow trout (mean weight, 2. g) were either left unhandled or intramuscularly (IM) injected with a standardized concentration of either a 48 or 72. h culture of C6-6 and subsequently challenged with two different doses of F. psychrophilum 7, 28 and 56. days post-injection (PI). The relative survival ranged from 66 to 87%, 42 to 53% and 0 to 18% at 7, 28 and 56. days PI, respectively. In the second study groups of rainbow trout (mean weight, 1.3. g) received either an intraperitoneal injection (IP) of phosphate buffered saline (PBS; negative control), supernatant from a C6-6 culture, formalin killed C6-6, or live C6-6 and were subsequently challenged with F. psychrophilum 7 or 28. days PI. Log rank survival analysis showed a significant (P