Characterization of two novel gene cassettes, dfrA27 and aadA16, in a non-O1, non-O139 Vibrio cholerae isolate from China

Two novel integron-borne cassettes, dfrA27 (encoding trimethoprim resistance) and aadA16 (encoding streptomycin and spectinomycin resistance), located on a conjugative plasmid, have been found in a non-O1, non-O139 Vibrio cholera isolate. DfrA27 shares 75% amino acid identity with DfrA5, and AadA16 shares 88% identity with AdaA6. Cloning of the cassette region and expression analysis demonstrated that the aadA16 gene can be expressed from its own promoter sequence, which is present upstream of the aadA16 cassette.