Construction of a gentamicin resistance gene probe for epidemiological studies

A 7.7-kilobase BamHI fragment was cloned from the transconjugant of a clinical isolate of Escherichia coli containing a 120-kilobase multiresistance IncC plasmid. The recombinant plasmid conferred resistance to kanamycin, gentamicin, tobramycin, sulfamethoxazole, and trimethoprim. This clone was used to generate a series of subclones from which a 2.0-kilobase BamHI-HindIII probe containing a gentamicin 2''-O-adenylyltransferase [AAD(2'')] gene was obtained. This probe hybridized specifically in both colony and Southern hybridizations with the AAD(2'') gene but not with other resistance genes, including other aminoglycoside-modifying genes, or with a reference IncC plasmid lacking the AAD(2'') gene. The AAD(2'') gene may be part of a transposon, since hybridization occurred with both nonconjugative plasmids and the chromosome in some isolates.