Study On Plasmid-encoded AmpC Beta-lactamases In Clinical Isolates Of Klebsierlla Peumoniae

Objective To investigate beta-lactamases and resistance of Klebsiella. pneumoniae in our Hospital, especially to study AmpCβ-lactamases and its genotypes mediated by plasmid in Klebsiella. pneumoniae. And to set up a method of AmpCβ-lactamases in clinic laboratory.Methods Bacterial identification and antibiotic susceptibility tests (MICs) were performed by France BioMerieux VITEK2 Compact system from clinical departments isolates between Sep 2006 and Aug 2007. Extend spectrum beta-lactamases were deteced by disc agar diffusion confirmatory method, AmpCs were screened by Cefoxitin disc agar diffusion method, then the positive strains were identified by three-dimensional method. and phenylboronic acid inhibitor based double-disk synergy test. The TEM-type, SHV-type and CTX-M-type ecoding genes were amplified by PCR. Multiplex PCR was used to detect ampC gene. The amplified ampC gene were sequenced and identified.Results Among total 137 strains of Klebsiella. pneumoniae, the positive rates of ESBLs were 37.2%(51 strains), the positive rates of Cefoxitin disc agar diffusion method were 16.1%(22 strains), the positive rates of three-dimensional method were 8.0%(11 strains). There were 18 and 11 positive strains in FOX/FOX+PBA andCTT/CTT+PBA group, respectively. Among 22 strains of Klebsiella. pneumoniae insusceptible to cefoxtin, PCR amplification showed the TEM-type in 10 strains, SHV-type in 6 strains and CTX-M-type in 6 strains. 19 strains of Klebsiella. pneumoniae were positive in Multiplex PCR amplification and identified all DHA-1-type AmpCβ-lactamases. The resistant rates of ESBLs producing strains Cefazolin, Ceftazidime, Ceftriaoxone, Cetepime and Aztreonam were all 100%,the resistance of AmpCs producing strains to Cefotetan was 36.3%. Both to Imipenem and ertapenem, the rates of resistance were 0%.Conclusions The resistance of Klebsiella. pneumoniae producing AmpCβ-lactamases show increase and clinical isolates of cefoxitin-resistant Klebsiella. pneumoniae often carry multi-type bla genes. FOX/FOX+PBA double-disk synergy test is fit for clinic laboratory. The prevalent of AmpCs producing Klebsiella. pneumoniae is DHA-1 genotype.