Translocation of antibiotic resistance determinants including an extended-spectrum beta-lactamase between conjugative plasmids of Klebsiella pneumoniae and Escherichia coli

Abstract

The extended-spectrum beta-lactamase CAZ-7, derived from TEMs, was produced by two different strains of the family Enterobacteriaceae, Klebsiella pneumoniae and Escherichia coli, isolated from the same patient. Both isolates were resistant to amikacin. In addition, the K. pneumoniae strain was TEM-1 producing and resistant to gentamicin. An E. coli HB101 transconjugant obtained from K. pneumoniae, selected on ceftazidime, showed that CAZ-7 and amikacin resistance were encoded by an 85-kb Inc7 or M plasmid, while an E. coli HB101 transconjugant obtained from E. coli under the same conditions showed that CAZ-7 and amikacin resistance were encoded by a greater than 150-kb Inc6 or C plasmid. Two other E. coli HB101 transconjugants obtained from K. pneumoniae, selected on gentamicin or chloramphenicol, showed that TEM-1 and gentamicin resistance could be encoded either by a greater than 150-kb Inc6 or C plasmid or by an 85-kb Inc7 or M plasmid. It was hypothesized that the genes for beta-lactam and aminoglycoside resistances were located on translocatable sequences. EcoRI digestion and hybridizations obtained with blatem, aacA4, and IS15 probes demonstrated that the CAZ-7 gene, amikacin resistance gene, and IS15 element were clustered on an approximately 20-kb fragment common to 85- and greater than 150-kb plasmids. E. coli HB101 transconjugants from K. pneumoniae and E. coli isolates were used to obtain translocations of CAZ-7 and amikacin resistance and of TEM-1 and gentamicin resistance between the 85- and greater than 150-kb plasmids. This study shows a typical example of in vivo gene dissemination involving transposable elements which translocate multiresistance genes, including an extended-spectrum beta-lactamase.