[Effect of temperature on the results of the antibiotic sensitivity test performed by the diffusion method in fish...

The sensitivity disk method is currently used in fish pathology to assess the efficacy of antimicrobial drugs. However, it is generally performed at temperatures lower than 37 degrees C, at which standard procedures were recommended by WHO. In order to check up the reliability of the results, selected strains and antibiotic substances were at once studied at 37 degrees C and 22 degrees C. In the last case, two readings of the zones of inhibition were done, after 24 and 48 h of incubation. Minimal inhibitory concentrations (MIC) had been determined using an agar-plate dilution method. Each association drug-bacterial strain provided three samplings of 30 measures which were compared by variance analysis and mean comparison tests. Variances did not differ, except with chloramphenicol and tetracyclines. But the mean values of the diameters significantly differed according to the incubation temperature. The variations could reach 7 to 8 mm, in any way. So, it appears that the disk method fails to allow any quantitative interpretation when performed at 22 degrees C. Consequences in diagnostic of fish diseases are stressed.