| Backgrounds:Enterobacteriaceae are important causes of community-acquired and hospital-associated infections, the severe abuse of antibiotics has promoted the rapid dissemination of Enterobacteriaceae resistant to drugs. At present, drug-resistance of Enterobacteriaceae gradually become a serious and universal problem, resulting in the ineffective clinical treatment of antimicrobial agents, increasing the cost of clinical treatment, shortening period of new antimicrobials application and development, threating the health of human directly. Cabapenems, such as imipenem and meropenem, diffuse easily into bacteria, and have a very broad spectrum of activity as the drugs, especially against many Gram-negative bacteria possessing extender-spectrumβ-lactamases (ESBLs) and AmpC enzymes. However, carbapenem-resistant gram-negative bacteria, particularly Acinetobacter baumannii and Pseudomonas aeruginosa, have been observed in some areas. The reports in Enterobacteriaceae were rare, especially in E. coli. In our study, we investigate the clinical infections caused by Enterobacteriaceae in ICU and the mechanism of carbapenem resistance in E. coli.Objective:A retrospective investigation was conducted to understand the clinical characteristics, risk factors, and bacterial resistance of the ICU patients infected with Enterobacteriaceae. Phenotypic and molecular characterization of carbapenem resistance with E. coli collected from ICU were analysed.Methods: 1. The cases with positive bacterial culture results in ICU were retrospectively investigated from 2003 to 2008.2. Resistance to carbapenem in Enterobaeteriaceae was isolated from patients in ICU in Anhui, China, and antimicrobial susceptibility was determined by the disk diffusion and agar dilution method.3.β-lactamases was analyzed by three-dimensional-test and EDTA-Na2-disk synergy test, which were recommended by the Clinical and Laboratory Standards Institute (CLSI),2009.4. Carbapenemase genotype was confirmed by Specific PCR and DNA sequencing.5. Transference of antimicrobial resistance was showed by conjunction experiment.Results:1. Of the isolated 139 strains from 87 patients, E. coli were 66.2%, Klebsiella pneumoniae were 19.4% and Enterobacter cloacae were 14.4%.82.6% of E. coli was resistant to ciprofloxacin, and 60.3% of Klebsiella pneumoniae to cotrimoxazole. The resistance rate of Enterobacter cloacae to cephalosporins was more than 75.0%. ESBLs-producing strains accounted for 60.9% in E. coli and 48.1% in Klebsiella pneumoniae. The factors highly correlated with multi-bacterial infection by Logistic Regression analysis were the usage of drugs in prehospital and immunosuppressive therapies (χ2=5.369, P<0.05;χ2=5.293, P<0.05). A significant association was also observed between multi-resistance and receipt of quinolones by experience.(χ2=3.893, P<0.05). 2. All the diulcalisolates were resistant toβ-lactam including penicillins, cephalosporins, aztreonam, carbapenem, andβ-lactamase inhibitors.3. The three-dimensional-test and EDTA-Na2-disk synergy test revealed that only one isolate produced carbapemase andβ-lactamase inhibitor failed to inhibit the hydrolyzing cathapenems.4. IMP-4 metallo-β-lactamase (MBL) was detected by PCR and DNA sequencing.5. Transformation assays of E. coli revealed that IMP-4 could be transferred from clinical isolate to recipient.Conclusions:The bacterial resistance is serious. Multi-bacterial infection was associated with the usage of drugs in prehospital and immunosuppressive therapies. Further surveillance of bacterial resistance should be carried out in ICU, and antimicrobial should be used according to the result of susceptibility testing. The blaIMP-4 genes encoding for resistance to carbopenems was the principal mechanism in E. coli. blaIMP-4 could be transferred from clinical isolate to recipient, which could easily result in the multidrug resistant phenotypes mediated by enzymes in isolates.
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