Establishment of Epidemiological Resistance Cut-Off Values of Aquatic Aeromonas to Eight Antimicrobial Agents

Abstract

The abuse of antibiotics in aquaculture has led to the increasing rate of antibiotic resistance of aquatic bacteria including <i>Aeromonas</i>, which is an increasing threat to environmental and human health. To date, no epidemiological cut-off values (CO_WT) for <i>Aeromonas</i> spp. have been established by the Clinical and Laboratory Standards Institute nor the European Commission on Antimicrobial Susceptibility Testing. In this study, commercially prepared minimum inhibitory concentration (MIC) test 96-well plates (dry-form plates) were used to determine the MIC of eight antimicrobial agents against 556 <i>Aeromonas</i> strains. The obtained MIC distributions were simulated and analyzed by NRI and ECOFFinder to obtain tentative CO_WT values for <i>Aeromonas</i> spp. The CO_WT values of eight kinds of representative antimicrobial agents including trimethoprim-sulfamethoxazole, erythromycin, doxycycline, neomycin, colistin, florfenicol, enrofloxacin, and ceftazidime for <i>Aeromonas</i> spp. were established and were 0.25, 64/32, 4/2, 8, 4, 1, 0.062/0.125, and 0.5 μg/mL, respectively. Results showed that <i>Aeromonas</i> spp. had a very high proportion of non-wild-type strains to enrofloxacin, florfenicol, and doxycycline, which are the most widely used antimicrobials in aquaculture. The CO_WT values for <i>Aeromonas</i> spp. obtained in this study can contribute to the final establishment of CO_WT for <i>Aeromonas</i> spp. internationally.