Antimicrobial Susceptibility and Local Epidemiological Cut-Off Values of Vibrio anguillarum Isolated From Fish Farms in Turkey

Studies on preventing antimicrobial resistance in aquaculture emphasise the need to responsibly and prudently use antimicrobials, selecting those most effective in controlling and/or reducing mortalities caused by vibriosis. In this study, the distribution of the antimicrobial susceptibility of 28 Vibrio anguillarum isolates from Turkish fish farms was determined using the broth microdilution minimum inhibitory concentration (MIC) test according to the Clinical and Laboratory Standards Institute (CLSI) guideline. The epidemiological cut-off (CO_WT) values of the V. anguillarum isolates of florfenicol (FLO), tetracycline (TET), doxycycline (DOX), oxolinic acid (OXO), enrofloxacin (ENR) and trimethoprim/sulfamethoxazole (SXT) were calculated using the normalised resistance interpretation (NRI) and ECOFFinder methods. Isolates were categorised as belonging to the fully susceptible wild-type (WT) or non-wild-type (NWT) populations. Calculated CO_WT values (in μg mL⁻¹) were ≤ 1.0 for FLO and DOX, ≤ 0.5 for TET, ≤ 0.016 for ENR, ≤ 0.032 for OXO, and ≤ 4.0 for SXT using the NRI analysis. Percentages of V. anguillarum isolates categorised as belonging to the NWT population were small for the antimicrobials FLO (10.7%) and SXT (0%), whereas they were higher for the antimicrobials OXO (39.3%) and ENR (39.3%). This is the first study to estimate the local CO_WT values for antibiotics used in the control of V. anguillarum isolates recovered from farmed fish in Turkey.