New Mg 2+ -Dependent Oxytetracycline Resistance Determinant Tet 34 in Vibrio Isolates from Marine Fish Intestinal Contents

Abstract

A new oxytetracycline (OTC) resistance (Otc^r) determinant, Tet 34, was cloned from chromosomal DNA of Vibrio sp. no. 6 isolated from intestinal contents of cultured yellowtail (Seriola quinqueradiata). The transformant, containing cloned Tet 34, could grow in broth containing 25 μg of drug per ml with 10 mM MgCl₂. Tet 34 encoded an open reading frame (ORF) 154 amino acids long. The amino acid sequence of the ORF was homologous to sequences of several bacterial xanthine-guanine phosphoribosyltransferases (XPRTs), which act in purine nucleotide salvage synthesis. Mg²⁺ binding site residues and the active site were highly conserved in XPRT and the ORF of Tet 34. The results suggest that Tet 34 encodes a new Mg²⁺-dependent Otc^r mechanism.