Multicenter Evaluation of the Xpert Carba-R Assay for Detection of Carbapenemase Genes in Gram-Negative Isolates

Abstract

This multicenter study evaluated the performance of the Cepheid Xpert Carba-R assay, a qualitative PCR test designed for the rapid detection of <i>bla</i>_KPC, <i>bla</i>_NDM, <i>bla</i>_VIM, <i>bla</i>_IMP, and <i>bla</i>_OXA-48 carbapenem resistance genes from bacterial isolates grown on blood agar or MacConkey agar. The results were compared to those obtained from bidirectional DNA sequence analysis of nucleic acid extracted from pure colonies. Isolates of <i>Enterobacteriaceae</i>, <i>Pseudomonas aeruginosa</i>, and <i>Acinetobacter baumannii</i> that tested as either intermediate or resistant to a carbapenem antibiotic were analyzed. A total of 467 isolates were evaluated, including prospectively collected clinical isolates, frozen isolates, and a group of contrived broth specimens sent by a central reference laboratory. The assay was run on the GeneXpert platform and took 48 min, with less than 1 min of hands-on time. Compared to the results of the reference methods, the overall sensitivity of the assay was 100% (95% confidence interval [CI], 99.0 to 100%) for isolates grown on both blood and MacConkey agars. Overall specificity was 98.1% (95% CI, 93.1 to 99.8%) and 97.1% (95% CI, 91.7 to 99.4%) for blood and MacConkey agars, respectively. This platform, previously demonstrated to be effective for the detection of carbapenemase genes in rectal swabs, is also adequate for the detection of these genes in bacterial colonies isolated from blood and MacConkey agars.