A novel large plasmid carrying multiple beta-lactam resistance genes isolated from a Klebsiella pneumoniae strain

Klebsiella pneumoniae clinical isolates were selected according to the resu lts of antibiotic susceptibility tests. Most of them were resistant to mult iple antibiotics, including ampicillin, ceftazidime, cefotaxime and aminogl ycosides. Large plasmids were observed in these Kl. pneumoniae strains by p ulsed-field gel electrophoresis with S1 nuclease digestion. The Kl. pneumon iae strains investigated produced one to two extrachromosomal bands with a mobility corresponding to 97 similar to 145 kbp linear DNA molecules. A 100 kbp plasmid, designated pK1, was observed in the multiply resistant strain K250. pK1 had sequences homologous to both the TEM-1 and the aphD probe wh ich were associated with beta-lactam and aminoglycoside resistance. pK1 was transformed into Escherichia coli strain DH5 alpha and was found to confer resistance to ampicillin, ceftazidime, cefotaxime and kanamycin. A 8 kbp B amHI DNA fragment of pK1 that carried the ampicillin resistance gene (minim um inhibitory concentration > 1000 mu g ml(-1)) was cloned into the BamHI s ite of pACYC184. Sequence determination showed that this cloned fragment ca rried a TEM-1 gene. These findings suggest that pK1 is novel in that it app ears to carry genes for resistance to ampicillin, cefotaxime and ceftazidim e, as well as kanamycin.