DETECTION OF TRANSFERABLE R-PLASMIDS IN STRAINS OF THE FISH-PATHOGENIC BACTERIUM, PASTEURELLA-PISCICIDA

Sixty strains of P. piscicida were collected from cultured yellow-tail, Seriola quinqueradiata Temminck and Schlegel, in various districts of Japan. These strains were tested for their sensitivity to 14 different chemotherapeutic agents and the detected drug resistant strains were investigated to determine whether they possessed R plasmids. All strains were most susceptible to ampicillin of the tested drugs. All except 5 strains were susceptible to chloramphenicol (CM) and doxycycline. The strains were only moderately susceptible to cefazolin, cephalexin, nalidixic acid, trimethoprim and ormetoprim, and their minimum inhibitory concentrations were < 3.1 .mu.g/ml. Twenty-one strains showed resistance to furazolidone (NF). Five of the 60 strains were resistant to CM, tetracycline (TC), kanamycin (KM), NF and sulfamonomethoxine (SA). Transferable R plasmids were detected in these drug-resistant strains. These R plasmids had markers for resistance to CM, TC, KM and SA.