[Plasmid-mediated cephalosporinase among extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae].

OBJECTIVE: To investigate the prevalence and genotype of plasmid-mediated cephalosporinase (AmpC) beta-lactamase in extended-spectrum-beta-lactamase-producing (ESBL) Escherichia coli and Klebsiella pneumoniae.

METHODS: 24 strains of cefoxitin-resistant ESBL-producing E. coli and 8 strains of K. pneumoniae were collected from January to December 2001 at Beijing Chaoyang Hospital. Analytical isoelectric focusing electrophoresis was used to measure the pI of the beta-lactamase. Conjugation experiment was used to study the transfer of cefoxitin resistance. The homology of the isolates was determined by pulsed field gel electrophoresis (PFGE). Plasmid-mediated AmpC enzyme genes were amplified and sequenced by using multiplex PCR.

RESULTS: The prevalence of ESBL-producing E. coli and K. pneumoniae were 16.8% (49/292) and 16.5% (35/212), respectively. The prevalence of AmpC enzyme among ESBL-producing E. coli and K. pneumoniae isolates were 2.0% (1/49) and 17.1% (6/35), respectively. These 7 isolates produced DHA-1 AmpC enzyme. One strain of K. pneumoniae could transfer cefoxitin resistance to the recipient. Among 7strains, 5 strains produced CTX-M-3 and 2 produced SHV-12 ESBL. These 7 strains also produced TEM-1 broad-spectrum enzymes. These strains harbored 2 - 5 plasmids and one of them were 33 - 36 kb. PFGE showed these strains came from a variety of clones.

CONCLUSIONS: In this hospital, 7 strains of the ESBL-positive E. coli and K. pneumoniae produced both DHA-1AmpC enzyme and CTX-M-3/SHV-12 ESBL. These 7 strains were from different clones.