engleski

Sea bass autochthonous bacterial isolates as potential probiotics for aquaculture: in vitro stimulation of host peripheral blood leukocytes

The aquaculture of the European sea bass Dicentrarchus labrax has been challenged by outbreaks of diseases, often occurring in intensive rearing systems. Increased administration of conventional chemotherapeutics can cause residue accumulation in marine environment and fish as final product and development of antimicrobial resistance, creating wrong image of aquaculture for the consumer. Probiotics, as an environmentally friendly prophylactic alternative, are beneficial and easy to use feed additives composed of live microorganisms that have an antimicrobial effect through modifying the intestinal microbiota, secreting antibacterial substances, competing with pathogens to prevent their adhesion to the intestine or for nutrients necessary for pathogen survival, eliciting an antitoxin effect and modulating the host immune system. It is proposed that bacteria of autochthonous origin have a greater capability to compete with resident pathogens and are also more prone to dominate and persist over other potentially pathogenic microbes. After random isolation of autochthonous gut bacteria of the European sea bass, their identification and pathogenicity testing, three potentially probiotic isolates were selected ; Pseudoalteromonas sp., Alteromonas sp., and Enterovibrio coralii. Selected isolates were tested and compared with a commercially available Lactobacillus casei isolate for their immunostimulative efficiency, inferring inflammatory, apoptotic and anti-pathogen response of sea bass’ peripheral blood leukocytes (PBLs). In order to evaluate early kinetics of the immune response, phagocytic activity, respiratory burst, and expression of lysozyme, Mx protein, caspase 3, TNF-α, IL-10 genes was measured 1, 3, 5, and 12 h post-stimulation by four bacterial isolates. Best immunostimulative properties were observed in Pseudoalteromonas- stimulated PBLs, followed by Alteromonas sp. and L. casei, while E. coralii failed to induce significant effect. In vitro assay results evidenced that intestinal autochthonous bacterial isolates have better immunostimulative properties on the host, compared to commercially available L. casei. A panel of biomarkers that represent pro-/anti-inflammatory, pro-/anti-apoptotic, and anti-bacteria/viral responses of the fish should be considered when evaluating the usefulness of the potential probiotic in aquaculture.

autochthonous bacteria, peripheral blood leukocytes, probiotic, sea bass

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