| Summary: | Probiotic bacteria have been widely studied in the past few decades as a viable, sustainable and efficient alternative to the existing method to prevent disease outbreak. Most commercial probiotics in animal husbandry are non-native species, which have been reported to fail settlement in the target organism. The aim of this project was to determine if the use of two probiotic-candidates, isolated from healthy wild turbot, could potentially exert beneficial effects on the immune status, inflammatory response and disease resistance of challenged juveniles in turbot farming, assessed upon rectal administration. The isolated bacteria were identified as closely related to Psychrobacter nivimaris and Psychrobacter faecalis, based on 16S rRNA (100% and 100% identity) and GYRB (96% and 97%) identification, respectively. This was evaluated experimentally by successive administrations of the respective probiotic (Pn, Pf) or, as control, PBS by rectal cannulation. Thereafter, fish were experimentally infected with the pathogen Tenacibaculum maritimum using a standardized immersion bath protocol. Virulence of the pathogen strain had previously been determined as LC50 after 7 d, assessing cumulative mortalities at 106, 107 and 108 CFU ml-1. To identify effects on the immune response, groups were assessed in triplicate before, 2 and 5 days post infection (0, 1 and 5 dpi), by determining gene expression of selected marker genes (mhc II α, il-1β, tcr, tgf β and tnf α) using RT-QPCR. In parallel, cumulative mortality over 14 days was studied at a higher pathogen concentration. Control-treated fish had marginally lower survival rates than fish that received one of the probiotic treatments. At 0 dpi, gene expression between treatments was comparable between treatments and control; only tgf, was decreased in the control group. At 1 dpi, gene expression of all genes was lower in the probiotic groups than in control fish. In contrast, at 5 dpi, no significant differences were observed between groups. As a conclusion, even though gene ...
|
|---|