Identification of a plasmid-mediated AmpC beta-lactamase from clinical isolates of Escherichia coli and Klebsiella pneumoniae

Objective To investigate the su sceptibility and genotype characteristics of Escherichia coli and Klebsiel la pneumoniae producing plasmid-mediated AmpC β lactamase. Method s A total of 110 strains of Escherichia coli and Klebsiella pne umoniae were collected from patients hospitalized in our respiratory ward duri ng January 2002-May 2004.The isolates harboring AmpC β-lactamase were detect ed by three-dimensional test,and isolectric focusing analysis,electroporation , PCR and DNA sequencing were performed to determine the genotypes. Results AmpC enzyme was detected in 9.0%(4/4) of the Escherichia coli isolates and 4.48%(/67) of the Klebsiella pneumoniae isolates. The susceptibility test showed 7 isolates tested were all resistan t to cefoxitin,and part of these strains were resistant to the third-generatio n cephalosporins,β-lactams/β-lactamase inhibitors,aztreonam,amikacin and ciprofloxacin,but most of them were susceptible to cefepime and imipenem. Thre e strains of Klebsiella pneumoniae and 2 strains of Escherichia coli tra nsferred cefoxitin-resistance to recipients by electroporation. Results of PCR and DNA sequencing defined them to be DHA-1 AmpC β-lactamase. Con clusion Escherichia coli and Klebsiella pneumoniae producing plasmid-mediated AmpC β lactamase were isolated from clinical strains in this hospital,and its gene can be transferred horizontally.