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

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.The increased intensification of aquaculture has led to a high number of disease outbreaks with an increasing range of pathogens. Consequently, the extensive use of broad-spectrum antibiotics in aquaculture has led, as in other fields, to drug resistance problems (32). In order to improve health and welfare in the rearing of these animals, several alternatives such as improved husbandry, nutrition, and water quality; lower stocking densities; and use of vaccines, nonspecific immunostimulants (7), and bacterial probiotics such as lactic acid bacteria (LAB) (9, 26) have been proposed.Probiotics are defined as microbial dietary adjuvants that beneficially affect the host physiology by modulating mucosal and systemic immunity, as well as improving nutritional and microbial balance in the intestinal tract (23).The role of LAB within the digestive tract of endothermic animals and humans has been extensively studied (14,18,28), while only a few studies have demonstrated that LAB are part of the normal intestinal microflora in larvae and juvenile fish (25). Most studies with probiotics conducted to date with fish have been undertaken with strains isolated and selected from aquatic environments and cultured animals. The main bacteria tested belonged to the genera Bacillus, Vibrio, and Pseudomonas (9, 22). Few authors have tested in vivo the protection conferred by probiotics in fish experimentally infected with pathogens. Gastesoupe (8) found that the Lactobacillus or Carnobacterium strain isolated from rotifers increased the resistance of turbot larvae against a pathogenic Vibrio sp. Gildberg et al. (10) demonstrated that Carnobacterium divergens decreased the mortality rate of Atlantic cod fry challenged with Vibrio anguillarum but not the mortality of salmon fry challenged with Aeromonas hy...

Effect of chemotherapy, vaccines and immunostimulants on innate immunity of goldfish infected with Aeromonas hydrophila

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Characterization of the intestinal microbiota of wild caught and farmed fine flounder (Paralichthys adspersus)

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Gnotobiotic zebrafish reveal evolutionarily conserved responses to the gut microbiota

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