Abstract :

Application of functional feed alternatives based on prebiotics and essential oils additive (PEA) to control furunculosis due to Aeromonas salmonicida subsp. salmonicida Aeromonas (ASS) is considered to reduce antibiotic use and perhaps antibiotic-resistant bacteria (ARB) and genes (ARG) in fish and environment. This study evaluated the efficacy of PEA against ASS through in vitro, in vivo and on-farm studies. In vitro results showed efficient antibacterial activity of PEA through micro dilution method. During 11 weeks of an in vivo study on 600 rainbow trout, PEA enhanced few immunity parameters, improved vaccine uptake and fish protection from ASS infection as well as growth performance after ASS inoculation, but the increase of disease resistance was not observed. A seven-months study on two rainbow trout farms did not show the protection effect of PEA on one of the farm detected with furunculosis into which antibiotic treatment was done. Fish, water and biofilm samples from these farms revealed that occurrence and abundance of ARB and ARG depended on Aeromonas origin, antibiotic use and presence of upstream activities. The link between fish and their environment by the detection of identical ARB and ARGs as well as a high risk of resistance genes developing and spreading in aquatic environments were observed. These collective facts from in vitro, in vivo and on-farm studies showed how far we still have to go in developing an efficient and practical alternative functional feed to reduce antibiotic use as well as decrease widespread transmission of Aeromonas ARB and ARGs in aquatics ecosystem relating to human and various animal species.

Key words :

Aeromonas, antibiotic-resistant bacteria, fish, functional feed alternatives, environment, resistance