Characterization of Plasmid-mediated AmpC type beta-Lactamase in Cefoxitin-resistant Klebsiella pneumoniae / 감염

ABSTRACT

BACKGROUND: Recently, new plasmid-mediated extended-spectrum beta-lactamases have been reported. These are not derived from TEM or SHV enzymes but are related to cephalosporins of Enterobacteriaceae (AmpCenzymes), that confer to all cephalosporins including cefoxitin. METHODS: Fifteen clinical isolates of cefoxitin-resistant Klebsiella pneumoniae were charaterized. Antimicroilutin method. Crude beta-lactamases were prepared by sonication and isoelectric focusing of the enzyme preparations was performed in polyacrylamide gel. The transmissibility of resistance was tested by mating to E. coli J53. We performed PCR and hybridization for further characterization of the AmpC-type beta-lactamse. RESULTS: Seven strains were found to have the plasmid-mediated AmpC type beta-lactamase as a pI of 8.0 and this was confirmed to be cmy-1 beta-lactamase by PCR and hybridization analysis. These strains were resistant to ampicillin and piperacillin with MICs above 128microgram/ml. Cefoxitin resistance could be transferred from 4 strains via a large plasmi with molecular sizes approximately 77 or 130 kb. The molecular weight of CMY-1 enzyme is approximately 38kDa. We analyzed the OMP of six cefoxitin-resistance K. pneumoniae. Two of six strains were lacking a major OMP of approximately 40 kDa, but four of them showed another 39 kDa sized band just below the 40 kDa major OMP, which were thought to be a modified 40 kDa OMP. CONCLUSION: With these results, we conclude that resistance to cefoxitin in K. pneumoniae isolated from Korean patients is either associated with the productin of CMY-a, a plasmid-mediated AmpC type beta-lactamase, of altered expressin of an outer membrane protein.