Efficiency of oxytetracycline treatment in rainbow trout experimentally infected with Flavobacterium psychrophilum strains having different in vitro antibiotic susceptibilities

Morten Sichlau Bruun, Lone Madsen, Inger Dalsgaard

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The medication effect of oxytetracycline on groups of rainbow trout fry experimentally infected with three strains of Flavobacterium psychrophilum was investigated. The infection model was based on intraperitoneal injection of the pathogen and treatment was done using medicated feed resulting in 100 mg oxytetracycline/kg fish for 10 days. The three F. psychrophilum strains had different antimicrobial susceptibilities and successful treatment was only obtained in the trial using a strain with a MICOTC of 0.25 mug/ml. No effect of treatment was seen in the group infected with a strain having MICOTC of 8.0 mug/ml and only little effect was seen when the strain MICOTC was 4.0 mug/ml. This shows that it is valid to predict the treatment efficiency of OTC from in vitro data facing an outbreak of rainbow trout fry syndrome. The importance of doing susceptibility testing is emphasized, and as shown the selection of media for antimicrobial susceptibility testing of F. psychrophilum is important. (C) 2003 Elsevier Science B.V. All rights reserved
Original languageEnglish
Issue number1-4
Pages (from-to)11-20
Publication statusPublished - 2003

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