FIG 4.

Deletion of ecnAB eliminates the probiotic benefit of Enterobacter C6-6. Four groups of fish (25 fish per group in triplicate) were fed a standard trout diet with feed supplemented with menhaden oil mixed with “ecnAB complement” (Enterobacter C6-6 ΔecnAB<pET101::ecnAB>), “C6-6 wild-type” (Enterobacter C6-6), “ecnAB knockout” (Enterobacter C6-6 ΔecnAB), or “No probiotic ctrl” (oil only; no added Enterobacter). After 10 days of supplemented feeding, these groups were challenged by subcutaneous injection with a virulent strain of F. psychrophilum (CSF 259-93). One group of fish (25 fish in triplicate) was fed the standard diet without any supplementation and served as a mock infection control. Daily mortalities were recorded for 28 days after infection. For this analysis, data were pooled across replicate treatment tanks (n = 3 per treatment), and statistical analysis was performed using the log rank test.