Antimicrobial Susceptibilities and Detection of Transferable R-Plasmids from Aeromonas hydrophila in Thailand

Sixty eight strains or Aeromonas hydrophila isolated in Thailand from cultured fishes, hu­mans, water of fishponds, and soft-shell turtles were tested for their susceptibility to 19 antimicrobial agents. All strains had intrinsic resistance to ampicillin. Fourteen strains were found to be susceptible to all drugs used except ampicillin, while the remaining54 strains were resistant to either cephazoline, chloramphenicol, streptomycin, tetracycline, sulfamonomethoxine, trimethoprim or furazolidone. The antibacterial activity of the pyridone carboxylic acids (new quinolones) was highest against all strains. Strains carrying plasmids encoded with resistance to tetracycline were detected in 9 or 54 resistant strains all or which were isolated from cultured snakehead (Ophicephalus striatus). The R-plasmids encoding resistance to chloramphenicol, tetra­cycline and sulfamonomethoxine were predominant. One strain encoded only for resistance to tetracycline.