Effect of seawater on the activity of antibiotics against isolated from the hemolymph of cultured pacific white shrimp.

Abstract

The purpose of this study was to eval-uate the effect of seawater (SW) on the activity of antibiotics belonging to 10 families (aminoglycosides,aminopenicillins, carbapenems,β-lactams, chlorampheni-cols, monobactams, nitrofurans, quinolones, sulfonamides,and tetracyclines) againstVibriostrains isolated fromhemolymph of Pacific white shrimp,Litopenaeus vannamei,farmed in Northeastern Brazil and standard strainVib-rio choleraATCC 19582. Susceptibility of the strains toantibiotics was determined by disk diffusion method andthe minimum inhibitory concentration was determined bymacrodilution method. The media Mueller–Hinton agar andbroth used in the above methods were diluted in distilledwater (control, 1% NaCl, pH 7.5) and SW (2.5% NaCl, pH7.5). The antibiotics most affected by dilution in SW weretetracycline, penicillin, cephalothin, aztreonam, ampicillin,and imipenem, as indicated by a considerable increase in thenumber of strains classified as intermediate or resistance.Thus, in this study, the efficiency of these antibiotics onVibriostrains was found to be reduced by contact with SW.