Comparison of the Xpert Carba-R and NG-Test CARBA5 for the detection of carbapenemases in an IMP-type carbapenemase endemic region in Japan

Abstract

Introduction: The real-time PCR assay Xpert Carba-R and the lateral flow immunoassay NG-Test CARBA5 were developed to detect 5 types of carbapenemase genes (bla_IMP, bla_KPC, bla_VIM, bla_OXA-48, and bla_NDM).

Methods: We compared the diagnostic performance, turn-around time, and cost of these assays. Carbapenemase genes were defined using the Carba NP test, modified Carbapenem Inactivation Methods (mCIM), multiplex PCR, and whole-genome sequencing. We included clinical Enterobacterales isolates (n = 36) and nonfermenting gram-negative bacilli isolates (n = 17) collected from 16 acute-care hospitals in the Kinki region of Japan.

Results: Twenty-six of these 53 isolates were positive according to both of the Carba NP test and mCIM and, contained the following carbapenemase genes: bla_IMP-1 (n = 3), bla_IMP-6 (n = 1), bla_IMP-19 (n = 12), bla_IMP-26 (n = 1), bla_IMP-41 (n = 2), bla_IMP-66 (n = 2), bla_NDM-1 (n = 3), and bla_VIM-2 (n = 2). All of the remaining 27 isolates were negative according to the Carba NP test, mCIM, and multiplex PCR. The specificities of both assays were 100%. The sensitivity of the Xpert Carba-R assay was as low as 53.8% and that of the NG-Test CARBA5 was 92.3% because the former failed to detect all isolates with bla_IMP-19 (n = 12) and the latter failed to detect isolates with bla_IMP-66 (n = 2). Both assays can easily be performed in less than 5 min.

Conclusions: The NG-Test CARBA5 assay was superior with regard to assay time and cost per sample. We propose the use of the NG-Test CARBA5 assay in clinical laboratories where IMP-type carbapenemases are endemic.

Keywords: Carbapenemase; IMP-type; NG-Test CARBA5; Xpert Carba-R.