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Study of antimicrobial susceptibility of Aeromonas isolates collected from diseased fish since 1984
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Edité par CCSD -
International audience. Introduction: Antimicrobial resistance is one of the major health challenges of the XXI century. In France, the “Ecoantibio” program aimed to reduce the use of veterinary drugs by 25% in 5 years. To assess the impact of this plan, an inventory of the situation is needed. In France, fish farming is a minor production not included in surveillance of antimicrobial resistance in animals. Very few data are available and the therapeutic arsenal is limited. Methodology: Three French laboratories managed a study on antimicrobial susceptibility of Aeromonas spp. isolates collected from diseased fish, by sharing their collections established since 1984. Harmonized protocols were used. The first step consisted in identifying isolates by MALDI-TOF. Motility and pigmentation reactions were also assessed to help identification at the species level. Secondly, antimicrobial susceptibility was tested by two methods: agar diffusion (AD) and broth dilution (BD). Twelve antimicrobial agents representing seven classes were chosen including agents labeled in French aquaculture (flumequine, oxolinic acid, trimethoprim-sulfamethoxazole, oxytetracycline and florfenicol). 120 isolates of Aeromonas mainly isolated from trouts (n=52, 43.3%) and turbots (n=52, 43.3%) were analyzed (27 old isolates and 93 contemporary isolates, collected in 1984–2000 and 2001–2014, respectively). Results: Aeromonas salmonicida was the most abundant species (n=77, 64.1%). Discrepancies were observed between MALDI-TOF identification and phenotypic traits. Out of the 77 isolates with A.salmonicida characteristic phenotype, the identification was confirmed for only 26 by MALDI-TOF. For the other 51 isolates, A. salmonicida identification was among the three first propositions of MALDI-TOF. Resistance to enrofloxacin, trimethoprim-sulfamethoxazole, flumequine and oxolinic acid was more frequent for the contemporary isolates compared to the oldest. In the same way, resistance to florfenicol and gentamicin was observed only in contemporary isolates whereas resistance to colistin and oxytetracycline seemed more prevalent among old isolates. AD and BD methods gave consistent results. Conclusions: A variation of antimicrobial resistance between old and contemporary isolates was observed. MALDI-TOF technology, in development in veterinary laboratories, is reliable for identification of Aeromonas spp. but the MALDI-TOF database should be improved to enable identification of Aeromonas isolates at the species level
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