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Members of the jury :

• Reviewers :
  • Nathalie CAROFF, Professor, Université de Nantes, France
  • Samira SARTER, Senior Manager, Cirad, Montpellier, France
• Examiners :
  • Brigitte LAMY, Associate Professor, Université Côte d'Azur, CHU de Nice, France
  • Ségolène CALVEZ, Associate Professor, Oniris, Nantes, France
  • Pascal SANDERS, Research Director, ANSES, Fougères, France
• Thesis Director : Hervé POULIQUEN, Professor, Oniris, Nantes, France
• Thesis co-director : Didier LEPELLETIER, Professor, Université de Nantes, CHU de Nantes, France
• Thesis co-supervisor : Emmanuelle MOREAU, Professor, Oniris, Nantes, France

Abstract :

Functional alternatives based on prebiotics and essential oils (PEA) against furunculosis due to Aeromonas salmonicida subsp salmonicida (ASS) are considered to reduce antibiotic use and possibly antibiotic resistant bacteria (ARB) and resistance genes (ARG). In vitro results showed effective antibacterial activity of PEA by the microdilution method. During 11 weeks of an in vivo study on 600 rainbow trout (TAC), AEP improved some immunity parameters, vaccine uptake, protection of fish against SSA infection as well as growth performance after SSA inoculation, but increase in disease resistance was not observed. A seven-month study on two TAC farms did not show the protective effect of AEP on one of the farms with furunculosis where antibiotic treatment was performed. Fish, water, and biofilm samples from these farms revealed that the occurrence and abundance of ARBs and ARGs depended on the origin of Aeromonas, antibiotic use, and the presence of upstream activities. The link between fish and their environment through the identical detection of WRAs and RGAs as well as a high risk of WRA and RGA development in aquatic environments was observed. The results of these studies have shown how far we have to go in the development of effective alternatives to reduce the use of antibiotics as well as to decrease the widespread transmission of WRAs and RGAs in the aquatic ecosystem in connection with humans and animals.