Molecular Analysis of Antibiotic Resistance Gene Clusters in <i>Vibrio cholerae</i> O139 and O1 SXT Constins

ABSTRACT Many recent Asian clinical Vibrio cholerae E1 Tor O1 and O139 isolates are resistant to the antibiotics sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm), and streptomycin (Sm). The corresponding resistance genes are located on large conjugative elements (SXT constins) that are integrated into prfC on the V. cholerae chromosome. We determined the DNA sequences of the antibiotic resistance genes in the SXT constin in MO10, an O139 isolate. In SXT MO10 , these genes are clustered within a composite transposon-like structure found near the element's 5′ end. The genes conferring resistance to Cm ( floR ), Su ( sul II), and Sm ( strA and strB ) correspond to previously described genes, whereas the gene conferring resistance to Tm, designated…