| Objectives To evaluate the detection ability and clinical application value of modified carbapenem inactivation test(m CIM)and EDTA-carbapenem inactivation method(eCIM)for different carbapenem genotypes and to analyze the characteristics of drug sensitivity in vitro and the distribution of minimum inhibitory concentration of Enterobacteriaceae bacteria carrying different carbapenem genes,so as to facilitate rational selection of medicines in clinic.Methods 1 80 strains of CRE isolated from clinical specimens in North China Uni versity of Science and Technology Affiliated Hospital from September 2018 to September 2019 were collected.Identification and drug resistance were tested by VITEK 2 Compact system.Phenotype screening and confirmation of CRE strains by means of m CIM,eCIM and the modified Hodge test.2 PCR was performed for carbapenem resistance genes(blaKPC,blaNDM,blaIMP,blaVIM,blaOXA-48),extended-spectrum ?-lactamase genes(SHV,TEM,CTX,OXA-1),the Amp C enzyme-encoding genes(DHA,FOX),and the membrane pore proteins Omp K35 and Omp K36 genes.3 Based on the results of PCR detection of carbapenemase genes as the gold standard,the consistency analysis of m CIM,eCIM and the modified Hodge test was carried out.4 The MICs of imipenem,meropenem,tegacycline,levofloxacin,trimethoprim/sulfamethoxazole,aztreonnam and colistin on CRE were further checked by E-test.5 The drug sensitivity of CRE in vitro and the MIC distribution of CRE strains with different carbapenemase genes were analyzed.Results 1 Distribution of strains Of the 80 CRE strains,60(75%,60/80)were Klebsiella pneumoniae and 17(21.3%,17/80)were Escherichia coli.The distribution of departments was mainly in ICU 38 strains(47.5%,38/80)and neurology ICU 23 strains(28.8%,23/80)respectively.58 strains(72.5%,58/80)were mainly respiratory specimens.2 Genotype test results 78 strains(97.5%,78/80)of 80 CREs were identified carrying the carbapenemase genes,including 54 strains(69.2%,54/78)only carring blaKPC-2,7 strains(9.0%,7/78)only carring blaNDM-5,and among 17 strains(21.8%,17/78)carrying blaKPC+NDM simultaneously 12 strains(15.4%,12/78)carrying blaKPC-2+blaNDM-5 and 5 strains(6.4%,5/78)carrying blaKPC-2+blaNDM-1;In addition,two strains with negative carbapenemase genes were found to have membrane porin deletion and positive ESBLs and Amp C genes.3 Phenotype screening resuls The positive rate of modified Hodge test was 100%(54/54,17/17)for strains carrying KPC-type and KPC+NDM-type carbapenem and 0% for NDM-type.The positive rate of KPC,NDM and KPC+NDM carbapenem genes detected by m CIM test was 100%(78/78).In eCIM test,one strain(1.9%,1/54)was positive in the strains with KPC type carbapenem only.There are 7 strains carrying only NDM type were all(100%,7/7)positive and 17 strains carrying only KPC+NDM-type were all negative.The results of consistency test showed that the overall detection rate of KPC,NDM and KPC+NDM carbapenem in the m CIM test was better than that in the modified Hodge test(kappa: 1.000 vs 0.101).The modified Hodge test showed good detection ability for strains with KPC type carbapenem(kappa: 1.000,P=1.000),but have no ability to detect in the strains with NDM carbapenem alone(kappa:-0.255,P=0.000);The eCIM test showed good detection ability for the strains with NDM type carbapenemase(kappa: 0.924,P=1.000).4 Drug resistance characteristics of different genotypes The resistance rates of 80 CRE strains to tegacyclin and polymyxin were 0%.The resistance rates of CRE strains carrying blaKPC to trimethoprim/sulfamethoxazole and amikacin were 48.1%(26/54)and 46.3%(25/54),respectively;The resistance rates of CRE with blaNDM to amikacin and aztreonam were 28.6%(2/7)and 42.9%(3/7),respectively;CRE with blaKPC and blaNDM had the lowest resistance rate to amikacin 47.1%(8/17).Two strains with deletion of membrane porins and positive genes of ESBLs and Amp C were sensitive to levofloxacin and trimethoprim/sulfamethoxazole.5 Distribution of MIC50/90 of different genotypes The MIC50/90 ratio of KPC-type CRE strains to trimethoprim/sulfamethoxazole was the lowest,which was 1/16?g/m L,the MIC50/90 of amikacin and the MIC50 of aztreonam were the lowest in NDM strains,which were 1/8?g/m L and 0.5?g/m L respectively.Conclusions 1 The m CIM test has good detection ability for KPC,NDM and KPC+NDM carbapenem.However,the modified Hodge test was has no ablity to detect NDM type carbapenem.2 The eCIM test was more sensitive to NDM carbapenem,but it lost the ability to detect CRE strains carrying both KPC and NDM genes.3 On the basis of m CIM test,further eCIM test can confirm the phenotype of CRE strains with different genotypes.4 There was no ability to detect the two strains with membrane porin deficiency and ESBLs or Amp C enzyme resistance for the m CIM,eCIM test and the modified Hodge test.5 Because the resistance of CRE strains with different genotypes is not samelar.It is recommended to select suitable antibiotics for CRE which drug resistance phenotypes is different.Figure 8;Table 11;Reference 202... |
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