5 research outputs found
Quelles stratégies alternatives aux antibiotiques en aquaculture ?
National audienceIn spite of restricting rules, antibiotics are still used in aquaculture for prevention, especially during critical phases (early stages; metamorphosis; transfer), but also during on-growing. Besides improving husbandry techniques and prophylaxis, which is still possible, alternative methods are now available or in progress. Commercial probiotics for land animals are increasingly used for shrimp and fish farming, though every species or rearing condition should require particular experiments to determine the most suitable microbial preparations and doses. The variability in response to probiotics, and the lack of reliable data hinder the use of such practices in routine, indeed. These commercial preparations contain Lactobacillus, Bacillus, or other bacteria belonging to related genera, or yeast. They are not suitable for bivalve molluscs like scallops, oysters, and clams. Only few marine bacteria have been documented to protect efficiently larval bivalves against infection. However, many problems remain unsolved regarding legal authorization, production, preservation, and retailing of such preparations with gram-negative bacteria. Probiotics may display multiple effects, possibly combining bacterial antagonism to some effects on the host, e.g. stimulating immunity, or growth, though the modes of action are not fully understood. Probiotics are not as efficient as antibiotics in case of bacterial infection, however. Prebiotics like fructo-oligosaccharides (FOS) may also improve animal health, since they favor the establishment of commensal or beneficial gut microbiota. For instance, an experiment showed that FOS could increase growth of turbot fry. A third alternative may come from antimicrobial peptides, which have been described in many organisms. These peptides have wide spectra of action. They can kill gram negative and gram positive bacteria, envelop viruses, yeasts, and moulds. Several peptides were recently discovered in shrimp and oysters, where they are essential elements of innate defense, in the absence of acquired immunity. These molecules could advantageously replace antibiotics, since they are less susceptible to cause resistance in the target microorganisms, due to their direct action on membranes, and to their fast degradability, which avoid the accumulation of residues.MalgrĂ© des rĂ©glementations contraignantes, lâusage des antibiotiques en prĂ©ventif est encore rĂ©pandu en aquaculture, particuliĂšrement pendant les phases critiques (stades prĂ©coces, mĂ©tamorphose, transferts dâanimaux), mais aussi chez des animaux en croissance. En plus des amĂ©liorations que lâon peut encore apporter en matiĂšre de zootechnie et de prophylaxie traditionnelle, des mĂ©thodes alternatives sont maintenant disponibles ou en dĂ©veloppement. Les prĂ©parations microbiennes commercialisĂ©es pour les Ă©levages terrestres sont de plus en plus utilisĂ©es pour les Ă©levages de crevettes et de poissons, mais chaque espĂšce ou Ă©levage demanderait des expĂ©rimentations particuliĂšres pour dĂ©terminer les produits et les doses les plus efficaces. En effet, les rĂ©ponses des animaux Ă lâajout des probiotiques peuvent ĂȘtre variables et lâabsence de donnĂ©es fiables freine leur application en routine. Les probiotiques dâorigine terrestre contenant des Lactobacillus, des Bacillus ou dâautres bactĂ©ries de genres connexes, ou bien encore des levures, ne conviennent pas pour les mollusques bivalves comme les huĂźtres, les coquilles St Jacques, les palourdes. Seules quelques bactĂ©ries marines sĂ©lectionnĂ©es protĂšgent les larves de bivalves contre les infections bactĂ©riennes. Cependant, lâutilisation pratique de ces bactĂ©ries gram (-) pose de nombreux problĂšmes dâautorisation lĂ©gale, de production, de conservation et de distribution. LâintĂ©rĂȘt des probiotiques rĂ©side dans leurs effets multiples, qui associent Ă des activitĂ©s antibactĂ©riennes, des effets sur lâhĂŽte telles que la stimulation de la rĂ©ponse immunitaire ou celle de la croissance, bien que les mĂ©canismes dâaction ne soient pas clairement identifiĂ©s. Par contre ils nâont pas la mĂȘme efficacitĂ© que les antibiotiques pour stopper une infection. Les prĂ©biotiques comme les fructo-oligosaccharides constituent une autre possibilitĂ© dâamĂ©liorer la santĂ© des animaux, et des essais ont montrĂ© leur efficacitĂ© chez les alevins de turbot par exemple. Une troisiĂšme alternative est reprĂ©sentĂ©e par les peptides antimicrobiens. Ces molĂ©cules ont un large spectre dâactivitĂ© antimicrobienne. Ils peuvent tuer des bactĂ©ries gram (-) et gram (+), des champignons ou des virus enveloppĂ©s. Plusieurs de ces peptides viennent dâĂȘtre dĂ©couverts chez les invertĂ©brĂ©s marins (crevettes et huĂźtres), oĂč ils sont un Ă©lĂ©ment essentiel de la dĂ©fense de ces animaux sans immunitĂ© acquise. Ils pourraient remplacer avantageusement les antibiotiques Ă terme. Ils devraient gĂ©nĂ©rer moins de rĂ©sistances chez les microorganismes cibles, car ils agissent sur les membranes cellulaires et ils devraient ĂȘtre plus vite dĂ©gradĂ©s sans produire de rĂ©sidus
Preliminary Study of the Effects of Commercial Lactobacilli Preparations on Digestive Metabolism of Juvenile Sea Bass <i>(Dicentrarchus labrax)</i>
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