Modified carbapenem inactivation method/EDTA-carbapenem inactivation method test to evaluate detection ability of carbapenemase and analyzing drug-resistance characteristics of carbapenem-resistant Enterobacteriaceae

Abstract:

Objective：To evaluate the detection ability of modified carbapenem inactivation method（mCIM）/EDTA-carbapenem inac－tivation method（eCIM） test and modified Hodge test for carbapenemase of different genotypes in Enterobacteriaceae，and to analyze the minimum inhibitory concentration（MIC） of carbapenem-resistant Enterobacteriaceae（CRE） on common clinical medicines，so as to aid the clinician to choose reasonable medicines. Methods：Forty CRE strains isolated from clinical specimens in our hospital from June 2018 to December 2018 were collected. VITEK 2 Compact automatic bacterial identification/drug sensitivity system was used to conduct the identification and drug sensitivity；E-test method was used to detect the imipenem，meropenem，tegacycline，amikacin，levofloxacin and compound sulfamethoxazole on MICs of CRE；broth microdilution method was used to detect the MIC of polymyxin. The mCIM/eCIM test and modified Hodge test were used to detect the situation of CRE to produce carbapen－emase. PCR was used to detect carbapenem resistance genes（blaKPC，blaNDM，blaIMP，blaVIM and blaOXA-48），extended-spectrum β-lactamase genes（SHV，TEM，CTX andOXA-1），AmpC enzyme-encod－ing genes（FOX），and membrane pore proteins ompK35 and ompK36 genes. Results：Among 40 CREs，38 strains carried the carbapen－emase gene，including blaKPC of 35 strains，blaNDM of 7 strains，blaKPC+blaNDM of 4 strains. Positive rates of the modified Hodge test，mCIM/eCIM test to KPC carbapenemase were 100%（38/38）. Positive rates of mCIM/eCIM test to NDM carbapenemase were 100%（3/3）. Positive rates of the modified Hodge test to NDM carbapenemase were 0. Drug resistance analysis：drug-resistance rates of 40 CRE strains to common clinical antibiotics，such as the third and the fourth generation of cephalosporins，enzyme inhibitor mix－ture，aztreonam，imipenem and meropenem，were all 100%；those to levofloxacin，amikacin and compound neotamin were 90.0%，60.0% and 42.5%，respectively. It is not found that strains were resistant to tigecycline and polymyxin. Conclusion：Both mCIM/eCIM test and modified Hodge test have high sensitivity to KPC carbapenemase，but mCIM/eCIM test is more sensitive than modified Hodge test to NDM carbapenemase，suggesting to select suitable antibiotics for CRE to different drug resistance phenotypes.