Performance of Xpert Carba-R Assay for Identification of Carbapenemase Gene in the Clinical Microbiology Laboratory

Abstract

Objectives The Xpert Carba-R Assay is a diagnostic test designed for the rapid detection and differentiation of the blaKPC, blaNDM, blaVIM, blaOXA-48, and blaIMP-1 genes. We verified the performance of Xpert Carba-R Assay for identification of carbapenemase gene in the clinical microbiology laboratory. Methods The analytical limit of detection was determined with two suspensions of carbapenemase-producing Enterobacteriaceae (CPE) isolates (KPC and NDM). A total of 52 specimens were evaluated: 21 bacterial isolates from clinical specimens, 21 rectal swabs, and 10 contrived stool specimens. Results In bacterial isolates, concordant results between the Xpert Carba-R Assay and PCR were found in 20 of 21; 8 KPC, 8 NDM, 1 IMP, and 2 multiple carbapenamase genes (KPC/NDM, NDM/OXA) were detected both by Xpert Carba-R Assay and PCR. In one GES-positive isolate, Xpert Carba-R Assay showed a negative result as expected. One VIM-positive isolate tested negative by Xpert Carba-R Assay. Complete concordance was seen in rectal swab specimens: 4 specimens with KPC and 17 specimens with negative results both by Xpert Carba-R Assay and surveillance culture. Among the 10 contrived stool specimens, Xpert Carba-R Assay detected carbapenemase genes in 9 specimens as expected according to the CPE strains spiked into the contrived stool; 2 KPC, 4 NDM, 1 IMP, and 2 multiple carabapenamase genes (NDM/KPC, NDM/OXA). One VIM-positive specimen tested negative by Xpert Carba-R Assay. Conclusion In conclusion, the Xpert Carba-R Assay can be used to identify carbapenemase gene in bacterial isolates cultured from clinical specimens and detect CPE carrier using rectal swab in clinical laboratories.