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

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.

Antimicrobial Resistance Pattern and Ribotyping of Shigella sonnei Isolated in Korea

Antimicrobial resistance, plasmid profile, and ribotype were determined from the 49 strains of Shigella sonnei isolated from 1992 to 1994 in Korea. Four patterns of antimicrobial resistance were shown. Based on the and microbial resistance test, 49 isolates of Shigella sonnei showed resistance to at least one antimicrobial drugs. These Shigella sonnei isolates are placed into 7 different plasmid profiles. Thirty-eight strains showed pattern III and pattern IV. From endonuclease analysis, twelve (Hind III), nine (Bam HI), seventeen (Eco RI) patterns of plasmid profile were shown. To determine whether ribotyping could be used to distinguish among Shiglla sonnei isolates, Southern hybridization studies were conducted. Shigella sonnri genomic DNA fragments by digestion with Sal I and ribotyping revealed five distinct patterns of ribotype (strains with patterns I, II, III, IV, and V) after hybridization with Escherichia coli 16s and 23s rRNAs. Compared with Sal I only a single pattern of ribotype by Hinc II was found. According to these data, Shigella sonnei strains in Korea seemed to be more than five clones. However, we cannot find consistent relationship among antimicrobial resistance, plasmid profile, and ribotyping. Thus it is needed to consider antimicrobial resistance, plasmid profile, and ribotyping for the epidemiological study of Shigella sonnei in Korea.