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Comparison of the Xpert CARBA-R Test and Phenotypical Tests for Detection of Carbapenemases Types in Multidrug Resistant K. pneumoniae Isolates by Huseyin A. Terzi, Ozlem Aydemir, Umit Kilic, Tayfur Demiray, Mehmet Koroglu, Mustafa Altindis, Unal Erkorkmaz

Background: The objective of this study is to evaluate the performance of the Xpert CARBA-R Test and the phenotyping confirmation tests (MHT, CIM, Mastdiscs, and Carba NP) for the detection of carbapenemases in multidrug resistant (MDR) Klebsiella pneumoniae isolates.
Methods: A total of 68 MDR K. pneumoniae isolates isolated from various clinical samples, were included in the study. The identification and antibiotic susceptibility tests of these isolates were performed using the VITEK®2 (BioMérieux, France) automated system. The Xpert CARBA-R test was used as the molecular method. The combined disc method was performed using Mastdiscs Combi-D70C that includes four antibiotic discs with specific in-hibitors. The modified Hodge test was performed on all isolates. Carbapenemase inactivation method (CIM) and Carba NP test was used for carbapenemase enzyme production.
Results: Of the 50 isolates detected to produce carbapenemase by the molecular method (Xpert CARBA-R Test), 45 (90%) were detected by MHT, 39 (78%) were detected by CIM, and 42 (84%) were detected by Mastdiscs, while all the 50 isolates were detected by the Carba NP test. When the Xpert CARBA-R Test was taken as a reference, significant differences were found between the Carba NP and Xpert CARBA-R Test. There was no significant difference between the other phenotypic methods and Xpert CARBA-R Test. The sensitivity of the MHT, CIM, combined disc, and Carba NP tests was calculated as 0.90, 0.78, 0.84, and 1 and their specificity was calculated as 0.83, 0.83, 0.83 and 0, respectively. According to the gold standard, the predictive power of MHT, CIM, and MAST methods was found to be statistically significant.
Conclusions: There are various methods of carbapenemase detection, including phenotypic and molecular methods. There is no single detection method that is valid and usable in all conditions. Laboratories should choose a suitable carbapenemase detection and confirmation method in line with their needs, economic conditions, and infrastructures. Although the detection of the presence of carbapenemase by molecular methods is fast and reliable, low-cost phenotypic tests can be used in laboratories that do not have this possibility. It is an important advantage that the combined disc method can also determine the enzyme type.

DOI: 10.7754/Clin.Lab.2019.190137