In Vitro Activity of Quinolone antibacterials against Selected Fish Pathogens.

Abstract

A comparison was made of the in vitro activities of five quinolone antibacterials (nalidixic acid, piromidic acid, oxolinic acid, flumiquine and miloxacin) currently used in aquaculture in Japan and five newer quinolones (ofloxacin, norfloxacin, enoxacin, ciprofloxacin and tosufloxacin), against selected fish bacterial pathogens.Of the earlier quinolones, flumiquine and oxolinic acid showed the highest bacteriostatic and bactericidal activities against Gram-negatives.The newer quinolones, however, showed considerably higher activities, with ciprofloxacin and tosufloxacin most active. The newer quinolones were also active against strains resistant to the earlier quinolones. Gram positive bacteria were resistant to all the earlier quinolones, but some strains were sensitive to the newer quinolones, particularly to ofloxacin, ciprofloxacin and tosufloxacin.The activities of the newer quinolones were found to be less affected by serum, pH or the addition of magnesium, than the earlier quinolones. The newer quinolones were considered to have potential for the treatment of Gram-negative, and possibly Gram-positive, bacterial fish pathogens.

Drugs in salmonid aquaculture – A review

“…Recent publications seem to indicate that the antibacterial properties of several quinolones are greatly influenced by the presence of cations in concentrations equal to those in seawater. Palmer et al (1992) demonstrated a significant influence of magnesium ions on the in vitro effect of`older' quinolones, but found a less pronounced effect on the newer fluoroquinolones. Pursell et al (1995) found in a 72 h assay an 8-fold increase in MBC (minimum bactericidal concentration) against A. salmonicida for flumequine when divalent cations were present in the medium compared to the same assay without these cations.…”