The identification of carbapenemase types in Enterobacteriaceae by using molecular assay and phenotyping confirmation tests

Abstract

In this study, we aimed to identify the molecular carbapenemase types of the Enterobacteriaceae isolates and to evaluate the performance of manually prepared and commercially available combination disc methods and the modified Hodge test. One hundred and forty carbapenemase producing isolates and 45 isolates as control group were included in our study. The Xpert CARBA-R test was used as the molecular method. Antibiotic susceptibility tests were performed using combined discs, manually prepared with APBA (3-aminophenyl boronic acid), DPA (dipicolinic acid), EDTA (Ethylene diamine tetra acetic acid), cloxacillin supplements and Mastdiscs Combi-D70C that includes four antibiotic discs with specific inhibitors and temocillin discs. The modified Hodge test was performed on all isolates. OXA-48 gene was identified in 129 isolates , the NDM gene was identified in 10 isolates and VIM in one isolate. Thirty inaccurate results (30/185, 16%) were detected by using the manually prepared confirmation test. The sensitivity and specificity of this test were identified respectively 85% and 73%. Also, the sensitivity and specificity of the Mastdiscs Combi-D70C were identified as 100%. Negative results were detected in 3 NDM isolates with the use of a modified Hodge test. Sensitivity and specificity were calculated for the modified Hodge test respectively 97% and 100%. Finally, molecular methods provide results rapidly but they are not always easily accessible. The modified Hodge test can be used only for screening as a first step test and is not one of the tests that can identify the type of the carbapenemase. When carbapenem-resistant Enterobacteriaceae are detected, a commercial kit like Mastdiscs Combi-D70 may be preferred instead of the manually prepared phenotypic verification tests.