Detection of Colonization by Carbapenemase-Producing Gram-Negative Bacilli in Patients by Use of the Xpert MDRO Assay

Abstract

cDetecting colonization of patients with carbapenemase-producing bacteria can be difficult. This study compared the sensitivity and specificity of a PCR-based method (Xpert MDRO) for detecting bla KPC , bla NDM , and bla VIM carbapenem resistance genes using GeneXpert cartridges to the results of culture with and without a broth enrichment step on 328 rectal, perirectal, and stool samples. The culture method included direct inoculation of a MacConkey agar plate on which a 10-g meropenem disk was placed and plating on MacConkey agar after overnight enrichment of the sample in MacConkey broth containing 1 g/ml of meropenem. Forty-three (13.1%) samples were positive by PCR for bla KPC and 11 (3.4%) were positive for bla VIM ; none were positive for bla NDM . The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay for bla KPC were 100%, 99.0%, 93.0%, and 100%, respectively, compared to broth enrichment culture and sequencing of target genes. The sensitivity, specificity, PPV, and NPV of the assay for bla VIM were 100%, 99.4%, 81.8%, and 100%, respectively. Since none of the clinical samples contained organisms with bla NDM , 66 contrived stool samples were prepared at various dilutions using three Klebsiella pneumoniae isolates containing bla NDM . The PCR assay showed 100% positivity at dilutions from 300 to 1,800 CFU/ml and 93.3% at 150 CFU/ml. The Xpert MDRO PCR assay required 2 min of hands-on time and 47 min to complete. Rapid identification of patients colonized with carbapenemase-producing organisms using multiplex PCR may help hospitals to improve infection control activities.

Evaluation of Carbapenemase Screening and Confirmation Tests with Enterobacteriaceae and Development of a Practical Diagnostic Algorithm

“…ETP screening with the EUCAST CBP for nonsusceptibility (Ͻ25 mm) also showed high sensitivity (100%) but low specificity (62.5%, Table 2). Thus, our results confirm the current EUCAST recommendation (15). The CLSI CBPs for ETP nonsusceptibility (Ͻ22 mm) and MEM nonsusceptibility (Ͻ23 mm) displayed lower sensitivity than the current EUCAST recommendation (95.5%, Table 2).…”

“…Molecular techniques comprise endpoint and real-time PCRs, as well as microarray techniques (15)(16)(17). Critical diameters and MICs of ertapenem (ETP), meropenem (MEM), and imipenem (IPM) and automated microdilution expert systems have been evaluated as screening methods (14,(18)(19)(20).…”

Rapid Identification of Five Classes of Carbapenem Resistance Genes Directly from Rectal Swabs by Use of the Xpert Carba-R Assay

“…A prior study described the performance characteristics of a pilot device, the Xpert MDRO assay (Cepheid, Sunnyvale, CA, USA), which detected bla KPC , bla NDM , and bla VIM (16). A modification of this assay, the immediate predicate device to the test evaluated in this study, added bla IMP and bla and was CE-IVD-cleared for use in the European markets (17).…”

Evaluation of the Rapidec Carba NP Test for Detection of Carbapenemases in Enterobacteriaceae

“…A continuously increasing number of tests have been described for carbapenemase detection, including commercially available or laboratory-developed tests based on phenotypic or molecular methods (7)(8)(9). Critical diameters or MICs for meropenem were recommended by EUCAST for carbapenemase screening and have been demonstrated to be highly sensitive (10,11).…”