Characterization of Plasmid-Mediated aphA-3 Kanamycin Resistance in Campylobacter jejuni

A total of 254 isolates of Campylobacter jejuni and three isolates of Campylobacter coli , isolated from Sweden, Canada, and Egypt, were screened for kanamycin resistance. Eight strains of C. jejuni contained large plasmids that carried the aphA-3 kanamycin-resistance marker. In six plasmids, the aphA-3 gene was located downstream of an apparent insertion sequence, designated IS 607 *, which showed a considerable similarity to IS 607 , characterized on the chromosome of some Helicobacter pylori strains. In contrast, the other plasmids carried the aphA-3 gene as a part of a resistance cluster. This included three resistance markers encoding 6′-adenylyltransferase ( aadE ), streptothricin acetyltransferase ( sat ), and 3′-aminoglycoside phosphotransferase type III ( aphA-3 ). The genetic organization of this resistance cluster suggests that it has been acquired by C. jejuni from a Gram-positive organism. The IS 607 * element was also observed in kanamycin-susceptible strains of C. jejuni on plasmids mediating tetracycline resistance. The kanamycin-resistance phenotype transferred along with tetracycline resistance by conjugation from four representative C. jejuni strains to a recipient strain of C. jejuni . The kanamycin-resistance determinant ( aphA-3 ) was stably transferred from one of the four C. jejuni strains to a recipient strain of Escherichia coli . However, the C. jejuni plasmid, which also carries the tetO gene, was not maintained in E. coli . Pulsed-field gel electrophoresis revealed the integration of approximately 50 kb of the plasmid into the chromosome of the E. coli recipient.