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

OBJECTIVE: To investigate the susceptibility and genotype characteristics of Escherichia coli and Klebsiella pneumoniae producing plasmid-mediated AmpC beta lactamase.

METHODS: A total of 110 strains of Escherichia coli and Klebsiella pneumoniae were collected from patients hospitalized in our respiratory ward during January 2002-May 2004. The isolates harboring AmpC beta-lactamase were detected by three-dimensional test, and isoelectric focusing analysis, electroporation, PCR and DNA sequencing were performed to determine the genotypes.

RESULTS: AmpC enzyme was detected in 9.30% (4/43) of the Escherichia coli isolates and 4.48% (3/67) of the Klebsiella pneumoniae isolates. The susceptibility test showed 7 isolates tested were all resistant to cefoxitin, and part of these strains were resistant to the third-generation cephalosporins, beta-lactams/beta-lactamase inhibitors, aztreonam, amikacin and ciprofloxacin, but most of them were susceptible to cefepime and imipenem. Three strains of Klebsiella pneumoniae and 2 strains of Escherichia coli transferred cefoxitin-resistance to recipients by electroporation. Results of PCR and DNA sequencing defined them to be DHA-1 AmpC beta-lactamase.

CONCLUSION: Escherichia coli and Klebsiella pneumoniae producing plasmid-mediated AmpC beta lactamase were isolated from clinical strains in this hospital, and its gene can be transferred horizontally.