Distribution of the Oxytetracycline Resistance Determinant Tet 34 among Bacteria Isolated from Diseased Fish

The distribution of a newly cloned oxytetracycline (OTC) resistance determinant, Tet 34, was examined among bacterial strains isolated from diseased fish. We analyzed 33 OTC-resistant strains isolated from 1998 to 2000 in Kagawa Prefecture. Tet 34 was detected in 3 of the strains, which were grouped in the genus Vibrio. Minimum inhibitory concentrations (MICs) of the 3 strains were higher than 500 μg/ml in the presence of MgCl2, and 125 or 250 μg/ml in its absence. Tet 34 was found in chromosomal DNA in all positive strains. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis of 16S rDNA revealed the 3 strains to have the same migration profiles. The sequences of their PCR products were also identical, suggesting that the species were the same. It was concluded that Tet 34 has been present since at least 1998, and the determinant occurs only in Vibrio species.