Improvement of the Xpert Carba-R Kit for the Detection of Carbapenemase-Producing Enterobacteriaceae

Abstract

The Xpert Carba-R kit, version 2 (v2), which has been improved for the efficient detection of bla OXA-181 and bla OXA-232 genes, was tested on a collection of 150 well-characterized enterobacterial isolates that had a reduced susceptibility to carbapenems. The performance of the Xpert Carba-R v2 was high, as it was able to detect the five major carbapenemases (NDM, VIM, IMP, KPC, and OXA-48). Thus, it is now well adapted to the carbapenemase-producing Enterobacteriaceae epidemiology of many countries worldwide. Carbapenemase-producing Enterobacteriaceae (CPEs) have been increasingly reported worldwide (1). The most clinically relevant carbapenemases encountered in Enterobacteriaceae belong to Ambler class A (KPC type); Ambler class B or metallo-␤-lactamases (MBLs), such as IMP, VIM, and NDM types; or Ambler class D (OXA-48-like) (1). In the United States and Europe, a mixture of KPC, NDM, VIM, and OXA-48-like carbapenemases dominates (1), while IMP-producing Enterobacteriaceae are more prevalent in the Far East (2). Carbapenem resistance may be the result of combined mechanisms of outer-membrane permeability defect (e.g., porin defect) and noncarbapenemase ␤-lactamases (e.g., acquired or overexpressed chromosome-encoded cephalosporinase and extended-spectrum ␤-lactamases) (1). However, it was recently demonstrated that despite having identical MICs for carbapenems, carbapenemase-producing Klebsiella pneumoniae exhibit a marked inoculum effect and were more resistant to the bactericidal effect of meropenem than were non-carbapenemase-producing K. pneumoniae (3). The finding suggested that MIC measurements alone are not sufficient to predict therapeutic efficacy of carbapenems against CPE and that the rapid detection of carbapenemase production is essential for the guidance of antimicrobial treatment (3). Finally, CPEs are known to be highly proficient in disseminating and causing outbreaks through highrisk lineages (e.g., KPC-producing K. pneumoniae ST258), and successful plasmids (e.g., IncL OXA-48 plasmid) (4, 5). Therefore, rapid confirmation of carbapenemase production is essential not only for effective therapy but also for the prompt implementation of infection control measures capable of preventing CPE dissemination (6).Molecular diagnostic assays have been increasingly used for the rapid screening of patients for carbapenemase producers directly from rectal swabs (7). Most of them can detect the four main carbapenemases (KPC, NDM, VIM, and OXA-48-like), which represent Ͼ95% of the carbapenemases produced by Enterobacteriaceae. The Xpert Carba-R kit (Cepheid, Sunnyvale, CA, USA) is the only commercially available assay that can also detect IMP-1 group producers (7). However, the Xpert Carba-R kit did not detect some OXA-48 variants, e.g., OXA-181 and OXA-232. Although still rare in France, the identification of these two variants rose from 0.8% in 2012 (8) to 3.4% in 2014 and 6.7% by mid-2015 of the total CPEs received at the French National Reference Centre for Antibiotic Resistance (L. Dortet, unpublishe...

OXA-244-Producing Escherichia coli Isolates, a Challenge for Clinical Microbiology Laboratories

“…Molecular detection of resistance genes. Using the commercially available Xpert Carba-R v2 assay, as recommended by the manufacturer (Cepheid, Toulouse, France) (15,16), bla OXA-48-like genes were detected in all seven OXA-244-Ec isolates. Wholegenome sequencing (WGS) was performed to determine the resistome of these OXA-244-Ec isolates using the ResFinder server (http://cge.cbs.dtu.dk/services/ResFinder-2.1) (17) ( Table 2).…”

False-Positive Carbapenem-Hydrolyzing Confirmatory Tests Due to ACT-28, a Chromosomally Encoded AmpC with Weak Carbapenemase Activity from Enterobacter kobei

“…Disk diffusion susceptibility testing revealed zone inhibition diameters for ertapenem at 20 mm and imipenem at 26 mm, which were below the epidemiological (13)(14)(15)(16). Antimicrobial susceptibility testing was also performed on Mueller-Hinton agar supplemented with cloxacillin.…”

“…kit (CORIS BioConcept, Gembloux, Belgium) for the detection of KPC, NDM, VIM, and OXA-48-like enzymes and the NG-CARBA 5 test (NG Biotech, Guipry, France) for the detection of KPC, NDM, VIM, OXA-48-like, and IMP enzymes (13)(14)(15). Finally, genes for KPC, NDM, VIM, OXA-48-like, and IMP enzymes were sought using the Xpert Carba-R kit (Cepheid, Sunnyvale, CA) (16).…”

CTX-M-15-Producing Shewanella Species Clinical Isolate Expressing OXA-535, a Chromosome-Encoded OXA-48 Variant, Putative Progenitor of the Plasmid-Encoded OXA-436

“…Bacterial colonies of Shewanella sp. JAB-1 recovered from Trypticase soy agar were used to perform Xpert Carba-R test version 2 (Cepheid, Sunnyvale, CA, USA), OXA-48 K-SeT assay (Coris BioConcept, Gembloux, Belgium), the Carba NP test, and the ␤ Carba test, according to the manufacturer's recommendations (22,34,35) or updated guidelines (36). The Carba NP test was also performed on recombinant E. coli TOP10 carrying pTOPO-preOXA-535.…”