Characteristics of Extended-spectrum beta-lactamase of Escherichia coli Strains Isolated from Clinical Specimens / 대한임상병리학회지

BACKGROUND: Recently Escherichia coli isolates with extended-spectrum beta-lactamase(ESBL) have been increased in Korea. ESBLs confer variable levels of resistance to cefotaxime, ceftazidime and other broad-spectrum cephalosporins as well as to monobactams such as aztreonam, but they have no detectable activity against cephamycins and carbapenems. The aim of this study was to characterize the ESBL produced by E. coli strains isolated from clinical specimens. METHODS: From March to July, 1998, a total of 93 clinical isolates of E. coli, which was produced ESBL, were collected from patients of the Asan Medical Center. The isolates flagged as ESBL producers by microbroth dilution antibiotic susceptibility test were confirmed by the double disk synergy test. Minimal inhibitory concentration(MIC) of beta-lactams were determined by agar dilution method. The presence of TEM, SHV or CMY-1 gene was determined by polymerase chain reaction. The types of beta-lactamase gene were determined by isoelectric focusing and nucleotide sequence analysis. RESULTS: Sixty-two strains carried plasmid-mediated TEM-52 gene, which sequence showed the substitution of 3 amino acids compared to that of TEM-1. Seventeen strains produced SHV-12, six strains produced SHV-2a, three strains produced TEM-52 and SHV-12, three strains produced TEM-52 and SHV-2a, and one strain produced SHV-2a and SHV-12. One out of twenty-seven strains of cefoxitin-resistant E. coli was confirmed to have CMY-1 beta-lactamase by PCR and nucleotide sequence analysis. CONCLUSIONS: TEM-52 was the most prevalent in E. coli isolates. The most common SHV-types of ESBL in Korea are SHV-12 and SHV-2a in E. coli isolates. In Korea, widespread use of oxyimino-cephalosporins in the hospitals has dramatically increased the prevalence of ESBL-producers in E. coli. Therefore, more prudent use of antibiotics is necessary to reduce the spread of these resistant organisms.

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.

The characteristics of extended-spectrum beta-lactamases in Korean isolates of Enterobacteriaceae

Extended-spectrum beta-lactamases (ESBLs) in gram-negative organisms have been implicated as the enzymes responsible for resistance to oxyimino-cephalosporins. The incidence of ESBL- producers in Korean isolates of Escherichia coli and Klebsiella pneumoniae were in the range of 4.8 7.5% and 22.5 22.8%, respectively. The ESBL-producing isolates revealed variable levels of resistance to cefotaxime, ceftazidime and aztreonam. They also showed the elevated MIC values of non-beta-lactam antibiotics. SHV-12 and SHV-2a were the enzymes most frequently found in K. pneumoniae strains, but TEM-52 was the most prevalent in E. coli isolates. About 15% of ESBL-producing isolates of Enterobacteriaceae produced CMY-1 enzyme, which conferred resistance to cephamycins such as cefoxitin as well as oxyimino-cephalosporins. Thus, the most common types of ESBLs in Korea are TEM-52, SHV-12, SHV-2a, and CMY-1.

Plasmid-encoded AmpC beta-lactamases: how far have we gone 10 years after the discovery?

The dogma that ampC genes are located exclusively on the chromosome was dominant until about 10 years ago. Since 1989 over 15 different plasmid-encoded AmpC beta-lactamases have been reported from several countries. Most of these enzymes evolved in two clusters. The major cluster includes several enzymes with a high similarity to CMY-2, which is the closest related chromosomal AmpC enzyme of Citrobacter freundii. A second cluster centers around CMY-1. It is less homogeneous and not closely related chromosomal AmpC enzymes. Molecular diversification by amino acid substitutions does not usually translate into a change in the resistance phenotype. At this time, CMY-2 appears to be the most prevalent and widely distributed. Further global increase of prevalence and diversity of plasmidic AmpC beta-lactamases have to be anticipated in the next millenium.