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

Detecting 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 detectingbla KPC ,bla NDM , andbla 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-μg meropenem disk was placed and plating on MacConkey agar after overnight enrichment of the sample in MacConkey broth containing 1 μg/ml of meropenem. Forty-three (13.1%) samples were positive by PCR forbla KPC and 11 (3.4%) were positive forbla VIM ; none were positive forbla NDM . The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay forbla 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 forbla VIM were 100%, 99.4%, 81.8%, and 100%, respectively. Since none of the clinical samples contained organisms withbla NDM , 66 contrived stool samples were prepared at various dilutions using threeKlebsiella pneumoniae isolates containingbla 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.