Identification of DHA-1 plasmid-mediated AmpC and CTX-M extended-spectrum- β-lactamase-producing Klebsiella pneumoniae in Beijing
Objective To investigate the prevalence and g en otype of plasmid-mediated AmpC β-lactamase among extended-spectrum-β-lact amase-producing Escherichia coli and Klebsiella pneumoniae. Methods Fifty-nine strains of cefoxitin-resistant ESBL-producing E.coli and 21 strains of K.pneumoniae were collected at two teaching hos pitals in Beijing during a period from 2001 to 2002. Analytical isoelectric focu sing was used to measure the pI of the β-lactamase. Conjugation experiment was used to study the transfer of cefoxitin resistance. Plasmid DNA was extracted a nd purified by Qiagen Plasmid Mini Kit. The homology of the isolates was determi ned by pulsed field gel electrophoresis(PFGE). Plasmid-mediated AmpC enzyme gen es were amplified and sequenced by multiplex PCR. Results At two hospitals in Beijing, the prevalence of plasmid-mediated AmpC among ES BL-producing E.coli and K.pneumoniae were 0 and 2%, 9.7% and 17.1%, res pectively. One isolate of E.coli and 9 K.pneumoniae produced DHA-1 plas mid-mediated AmpC enzyme. They also produced ESBL(CTX-3 type, 6 isolates; CTX -M-14, 1 isolate; SHV-12 type, 3 isolates). Three strains of K.pneumoniae can transfer cefoxition resistance to the recipient. These strains harbored at least one big plasmid with the size of 33-36 kb. Plasmid spreading was not prov ed. PFGE found these 10 strains came from a variety of different clones. Couclusion The clinical isolates of K.pneumoniae producing D HA-1 plasmid-mediated AmpC enzyme and CTX-M ESBL were found in Beijing. They ori from multiple different clones.