Evaluation of Immunomodulatory Effects of Lactic Acid Bacteria in Turbot ( Scophthalmus maximus )

Abstract

ABSTRACT In the present work, the effects of several lactic acid bacteria on the immune response of turbot ( Scophthalmus maximus ) macrophages have been studied both in vitro and in vivo. Out of six lactic acid bacterial strains tested, only heat-killed Lactococcus lactis significantly increased the turbot head kidney macrophage chemiluminescent (CL) response after 24 h of incubation. Nitric oxide (NO) was also significantly enhanced by this bacterium after 72 h of incubation with either viable (10 3 and 10 6 cells/ml) or heat-killed (10 6 cells/ml) bacteria. Viable Leuconostoc mesenteroides (10 6 cells/ml) was also capable of significantly increasing NO production. Since L. lactis proved to be the strain with more effects on the host immune function, further in vivo and in vitro experiments were conducted with this bacterium. The in vitro capacity of L. lactis to adhere to turbot intestinal mucus was positively confirmed. When orally administered, L. lactis significantly increased the macrophage CL response and the serum NO concentration after 7 days of daily administration. The antibacterial effect of the extracellular products from the six LAB strains against the fish-pathogenic bacterium Vibrio anguillarum was also demonstrated in vitro.