The Thai Journal of Veterinary Medicine


Florfenicol (FF) and Chloramphenicol (CAP) were tested for their in vitro antimicrobial activity against 102 Vibrio isolates from clinical cases. The Minimum Inhibitory Concentration (MIC) for both antimicrobials was ≤ 8 μg/ml suggesting that all of the tested isolates were susceptible to both antimicrobials. The observed MIC range of FF (0.5-4.0 μg/ml) was more potent than that of CAP (0.5-8.0 μg/ml). The activity of both antimicrobials was not substantially influenced by the addition of sea water (5 ppt salinity) to the test system. When considering the best type of antimicrobial for food producing animals and in vitro antivibrio activity, FF is a good prospect for the treatment of shrimp Vibrio pathogens. Accordingly an in vivo study was conducted on 3-month old black tiger shrimps, Penaeus monodon (14.5 ± 1.0 g) which were fed for 5 days with FF medicated feed at 0.8 g of FF per kilogram of feed, and 2.5% of the shrimps body weight. Florfenicol-amine (FFA), the marker residue of FF, was measured in the hepatopancreas and muscle using High Performance Liquid Chromatography (HPLC) and UV detection. The FFA concentration in samples from control shrimp was zero using these methods. The maximum concentration of FFA (Cmax) detected in the hepatopancreas after 1 hour (Tmax) was 0.7 μg/g tissue, and Cmax in the muscle was 0.05 μg/g tissue 4 hours (Tmax) after the initial medication. The average concentrations of FFA analyzed every 24 hours after medication were 0.54±0.04 μg/g in the hepatopancreas and 0.15±0.02 μg/g in the muscle. By the seventh day, following the cessation of feeding the medicated feed, the drug residue in the shrimp hepatopancreas and muscle, was lower than any detectable limits for the methods used (0.01 μg/g).



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