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

The abuse of antibiotics in aquaculture has led to the increasing rate of antibiotic resistance of aquatic bacteria including , which is an increasing threat to environmental and human health. To date, no epidemiological cut-off values (CO) for 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 strains. The obtained MIC distributions were simulated and analyzed by NRI and ECOFFinder to obtain tentative CO values for spp. The CO values of eight kinds of representative antimicrobial agents including trimethoprim-sulfamethoxazole, erythromycin, doxycycline, neomycin, colistin, florfenicol, enrofloxacin, and ceftazidime for 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 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 values for spp. obtained in this study can contribute to the final establishment of CO for spp. internationally.