Patterns of resistance to florfenicol and bicyclomycin in Brazilian strains of motile aeromonads

The minimum inhibitory concentration (MIC) and diameter of zone of inhibition of florfenicol (FLO) and the MIC of bicyclomycin (BCM) were determined for 118 motile aeromonad strains isolated from diseased fish and pond water in Brazil. Tests were performed according to Clinical and Laboratory Standards Institute guidelines. FLO MIC values ranged from 0.5 to 16 μg/mL and BCM MIC values from 0.78 to 100 μg/mL. According to MIC frequency distributions, the strains were classified as wild-type (WT) and non-wild-type (NWT) and provisional epidemiological cutoff values for FLO (WT ≤ 4 μg/mL) and BCM (WT ≤ 6.25 μg/mL) were estimated. Disk susceptibility tests revealed a provisional epidemiological cutoff of WT ≥ 23 mm for FLO. The lack of groups of bacterial strains with NWT behavior to FLO and BCM suggests that the estimated cutoffs should be revised in the future. Both antibiotics exhibited high efficacy in vitro against motile aeromonad strains.