Determination of Beta-haemolytic Activity and Minimum Inhibitory Concentrations of Antimicro- Bial Drugs against Aeromonas Hydrophila Strains Isolated from Fish Products

The purpose of the study was to investigate the prevalence of β-haemolytic Aeromonas hydrophila strains in 83 samples from cooled horse mackerel, rainbow trout, Black sea roach, silver carp, vacuum-packed rainbow trout fillets and 20 samples frozen rainbow trout and to establish the minimum inhibitory concentrations (MIC) of several antimicrobial drugs against these strains. Forty-five Aeromonas spp. strains were isolated, 36 (80%) of them with β-haemolytic activity. Identification of biochemical properties and determination of MICs were performed with 20 β-haemolytic A. hydrophila strains. The MICs of cefoxitin (≤0.5–32 μg/mL), azithromycin (≤0.5–16 μg/mL), chloramphenicol (≤2–16 μg/mL), tetracycline (≤4–16 μg/mL), ceftriaxone (≤0.25–32 μg/mL), amoxicillin/clavulanic acid (≤8/4–32/16 μg/mL), ciprofloxacin (≤0.015–1 μg/mL), gentamicin (≤1–4 μg/mL), nalidixic acid (≤0.5–8 μg/mL), ceftiofur (≤1–8 μg/mL), sulfisoxazole (≤64–256 μg/mL), trimethoprim/ sulfamethoxazole (≤0.12/2.38–1/19 μg/mL), kanamycin (≤8–16 μg/mL) and streptomycin (≤32 μg/mL) were determined using Sensititre® CMV2AGNF microtitre plates (Trek Diagnostic Systems, USA). Tested strains were resistant to ampicillin concentrations in the plate: >32 μg/mL.