In vitro antibacterial effect of seven chemotherapeutic agents were tested against
F. columnaris strains, and also therapeutic effect were examined on artificially infected
F. columnaris disease of cultured eel.
1) Minimum inhibitory concentration (MIC) of these agents to 15 strains of
F. columnaris isolated from eel were as follows.
MIC of NFS-Na was 0.009-0.31 mcg/ml, FZD was 0.039-1.25 mcg/ml, CP was 1.25-5.0 mcg/ml, OTC was 0.156-0.62 mcg/ml, SMM was 12.5-50 mcg/ml. OA was 0.156-5.0 mcg/ml and PL-B was over 100 mcg/ml.
2) Bactericidal effect of NFS-Na to strain EU-1 was same as those of OTC and OA at 1 mcg/ml. And thier bactericidal time were within 8 hours. While bactericidal time of NFS-Na to strain EU-3 was within 2 hours, FZD and OA were within 8 hours, and OTC was within 24 hours. But CP did not show bactericidal effect to both two strains as others.
3) Longer time of dipping inoculation and higher environmental temperature on the experimental infection in young ell with
F. columnaris induced low effect on the therapeutic effect of NFS-Na and FZD by medicated bathing.
4) Therapeutic effect of chemotherapeutic agents by medicated bath against experimental infection in young eel with the strain
F. columnaris EU-1 and EU-3 were as follows.
Effective concentration of NFS-Na was 0.0625-0.125 mcg/ml, FZD was 0.125-0.5 mcg/ml, CP was 0.25-2 mcg/ml, OTC was 0.0625-0.125 mcg/ml, and OA was 0.125-0.25 mcg/ml.
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