Research On Mechanisms Of Antimicrobial Resistance Among Carbapenem-resistant Enterobacteriaceae

ObjectiveThe main objective of this study is to investigate the main mechanisms of Enterobacteriaceae resistant to carbapenems. To provide the theoretical guidance for the rational use of antimicrobial agents and the scientific basis for controling the drug-resistant strains. Methods1. The carbapenems-resistant Enterobacteriaceae bacteriaisolated from the clinical laboratory of the First hospital of Jilin University.2. The resistance of carbapenems-resistant Enterobacteriaceae for 20 antimicrobial agents were determined using paper disk method and minimum inhibitory concentration(MIC)method, analyzed the drug-resistant spectrum.3. Modified Hodge test and Carba NP test were used to detect carbapenemase of carbapenems-resistant Enterobacteriaceae.4. Polymerase chain reaction(PCR)was determined to detect 23 kinds of drug-resistant genes and analyzed the types of drug-resistant genes for every carbapenems-resistant Enterobacteriaceae.5. Real-time PCR was carried out to investigate the expression level of porins’ genes.6. Read the case histories of 12 patients, analyzing the influenced factors of CRE strains’ appearance. Results1. Twelve strains of Enterobacteriaceae resistant to carbapenems inculding 4 strains of Klebsiella pneumoniae, 4 strains of Enterobacter cloacae, 1 strain of Citrobacter freundii, 1 strain of Klebsiella oxytoca, 1 strain of Escherichia coli and 1 strain of Morganella morganii.2. The drug-resistant rates of the 12 isolated strains to meropenem and imipenem were 75%. 12 strains were all resistant to ceftazidime, ceftriaxon, cefotaxim, cefepime, cefuroxim, cefoperazon/sulbactam, cefoxitin. The rates of Enterobacteriaceae resistant to levofloxacin and ciprofloxacin were 58%. The rates of Enterobacteriaceae resistant to cotrimoxazole, piperacillin/tazobactam and amikacin were 83%, 33% and 17% respectively.3. Modified Hodge tests were positive in 8 of 12 carbapenems resistance among Enterobacteriaceae strains, including 1 strain of Klebsiella oxytoca, 3 strains of Klebsiella pneumonia and 4 strains of Enterobacter cloacae.4. Carba NP tests were positive in 9 of 12 carbapenems resistance among Enterobacteriaceae strains, including 1 strain of Klebsiella oxytoca, 4 strains of Klebsiella pneumonia and 4 strains of Enterobacter cloacae.5. Among the 23 kinds of drug-resistant genes, 10 drug-resistant genes were detected, including blaIMP-1, blaIMP-2, blaCTX-M-1, blaCTX-M-2, blaCTX-M-9, blaSHV, blaACC, blaDHA, blaqnr B, blaqnr S.6. By using Real-time PCR technique to analyze the expression level of porin genes, we found that expression of Omp K36 gene in 3 Klebsiella pneumoniae strains, and Omp F, Omp C gene in 2 Enterobacter cloacae strains were decreased. The other two Enterobacter cloacae strains showed relative decreased expression of Omp C gene.7. Twelve strains of Enterobacteriaceae resistant to carbapenems mainly from the surgical ward(8 cases), 1 case from ICU, 1case of infectious diseases department, 1 from neurology, 1 from pediatric respiratory medicine. Except 2 cases others all have been operated, and 11 patients have been antimicribal agents therapied. Conclusions1. Twelve strains of Enterobacteriaceae resistant to carbapenems were screened by analyzing the drug resistance spectrum in the research, which has strong resistant to antimicrobial agents.2. Carba NP test has the advantages of accuracy and speed, should be preferred in clinical laboratory to test carbapenemase.3. Twelve strains of Enterobacteriaceae resistant to carbapenems simultaneously carry multiple resistance genes.4. The carbapenems-resistant Klebsiella pneumonia and Escherichia coli have been the mechanism of the decrease of porin expression.