Evaluation of Xpert Carba-R for detecting carbapenemase-producing organisms in South Africa

This study evaluated the performance of the Xpert Carba-R assay for detecting the five common carbapenemases in carbapenemase-producing organisms in Johannesburg, South Africa between April 2021 and September 2021. The assay demonstrated 98% sensitivity and 97% specificity. It was also able to detect all the carbapenemases in double carbapenemase producers, as well as carbapenemases in non-fermenter organisms. The Xpert Carba-R assay, therefore, allows the rapid (< 1 h) and accurate identification of the common carbapenemases in pure bacterial cultures and rectal swabs. This assay can aid in the timeous institution of appropriate treatment and infection prevention and control measures.

Deceased donors with multidrug-resistant organisms: implications and future directions

PURPOSE OF REVIEW

Organ utilization from donors infected or colonized with multidrug-resistant organisms (MDROs) remains inconsistent, and hesitancy to accept organs from these donors may relate to poor outcomes among solid organ transplant recipients with MDRO donor-derived infections (DDIs). An improved understanding of the risk factors for donor MDRO colonization or infection and the risk of MDRO DDI is needed to safely expand the donor pool while minimizing unnecessary organ discard.

RECENT FINDINGS

Recent studies have begun to delineate risk factors for MDRO acquisition among deceased donors and the epidemiology of MDRO DDIs, but additional efforts are warranted to inform optimal approaches to donor evaluation, risk stratification, management, interfacility and interagency data sharing, and approaches to recipient management.

SUMMARY

This review summaries recent data regarding risk factors for MDRO colonization and infection in deceased donors, epidemiology of MDRO DDIs, and current approaches to donors harboring MDROs and provides a framework for future research and collaboration.

White paper on antimicrobial stewardship in solid organ transplant recipients

Antimicrobial stewardship programs (ASPs) have made immense strides in optimizing antibiotic, antifungal, and antiviral use in clinical settings. However, although ASPs are required institutionally by regulatory agencies in the United States and Canada, they are not mandated for transplant centers or programs specifically. Despite the fact that solid organ transplant recipients in particular are at increased risk of infections from multidrug-resistant organisms, due to host and donor factors and immunosuppressive therapy, there currently are little rigorous data regarding stewardship practices in solid organ transplant populations, and thus, no transplant-specific requirements currently exist. Further complicating matters, transplant patients have a wide range of variability regarding their susceptibility to infection, as factors such as surgery of transplant, intensity of immunosuppression, and presence of drains or catheters in situ may modify the risk of infection. As such, it is not feasible to have a "one-size-fits-all" style of stewardship for this patient population. The objective of this white paper is to identify opportunities, risk factors, and ASP strategies that should be assessed with solid organ transplant recipients to optimize antimicrobial use, while producing an overall improvement in patient outcomes. We hope it may serve as a springboard for development of future guidance and identification of research opportunities.

Accuracy of Xpert Carba-R Assay for the Diagnosis of Carbapenemase-Producing Organisms from Rectal Swabs and Clinical Isolates: A Meta-Analysis of Diagnostic Studies

The Cepheid Xpert Carba-R assay has demonstrated a promising value for the detection of carbapenemase-producing organisms, but its diagnostic performance remains unclear. Studies were retrieved from Cochrane Library, EMBASE, and PubMed databases according to predetermined selection criteria. The specificity, sensitivity, negative likelihood ratio, positive likelihood ratio, and area under the summary receiver operating characteristic curves of Xpert Carba-R were analyzed by STATA version 13.0. The quality of each study was examined by Quality Assessment of Diagnostic Accuracy Studies using RevMan version 5.2. In total, 17 unique studies involving 15,972 samples met the inclusion criteria. Nine studies performed Xpert Carba-R on rectal swabs. The pooled sensitivity, specificity, and area under the curve were as follows: 0.95 (95% CI, 0.91-0.97; I² = 90.80%), 0.99 (95% CI, 0.97-0.99; I² = 97.17%), and 0.99 (95% CI, 0.98-1.00), respectively. The sensitivity and specificity of Xpert Carba-R in high-risk populations were 0.99 (95% CI, 0.76-1.00; I² = 78.51%) and 0.98 (95% CI, 0.97-0.99; I² = 84.95%), respectively. The sensitivity and specificity in low-prevalence regions were 0.96 (95% CI, 0.88-0.99; I² = 74.58%) and 0.99 (95% CI, 0.98-0.99; I² = 77.66%), respectively. Eight studies performed Xpert Carba-R on clinical isolates. The pooled sensitivity and specificity were 1.00 (95% CI, 0.97-1.00; I² = 97.43%) and 0.98 (95% CI, 0.97-0.99; I² = 55.27%), respectively. This meta-analysis indicates that Xpert Carba-R assay has excellent diagnostic accuracy for diagnosing carbapenemase-producing organisms on rectal swabs and clinical isolates, especially for high-risk populations and low-prevalence regions.

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

Introduction

High mortality associated with carbapenemase-producing Gram-negative bacteria (CP-GNB) has evolved into a global health threat. Rapid and accurate detection as well as prompt treatment are of great significance in this case. Xpert Carba-R, a multiple qualitative analysis designed to detect five clinically relevant carbapenem-resistant gene families within one hour, is regarded as reliable, accurate, and easy-to-operate. This study is to present a systematic evaluation of the performance of Xpert Carba-R in detecting carbapenemase genes in GNB suspected for carbapenemase production.

Methods

We searched and screened the literature on “Xpert Carba-R” in the database of PubMed, Web of Science, Embase, and Cochrane Library, employing two independent evaluators to collect data, respectively. Then, statistical analysis of the data obtained was performed by the Stata 12.0 software to measure the accuracy of Xpert Carba-R assay in detecting the carbapenemase genes in GNB.

Results

We screened a total of 1767 Gram-negative bacillus isolates documented in 9 articles. The precision of the detection of OXA-48 carbapenemase genes was 100%; that of NDM = 100%; that of VIM = 100%. When it came to KPC, the precision rate was 100%; that of IMP = 99%. The overall accuracy of the detection of carbapenemase genes was 100%.

Conclusions

Xpert Carba-R assay demonstrates a 100% precision in identifying carbapenemase genes in GNB. It can be seen that Xpert Carba-R method is an effective tool for early clinical detection, which is suitable for the detection of carbapenase gene in GNB.

Direct detection of OXA-48-like carbapenemase variants with and without co-expression of an extended-spectrum β-lactamase from bacterial cell lysates using mass spectrometry

INTRODUCTION

Antibiotic-resistant Gram-negative bacteria are of a growing concern globally, especially those producing enzymes conferring resistance. OXA-48-like carbapenemases hydrolyze most β-lactam antibiotics, with typically low-level hydrolysis of carbapenems, but have limited effect on broad-spectrum cephalosporins. These are frequently co-expressed with extended spectrum β-lactamases, especially CTX-M-15, which typically shows high level resistance to broad-spectrum cephalosporins, yet is carbapenem susceptible. The combined resistance profile makes the need for successful detection of these specific resistance determinants imperative for effective antibiotic therapy.

OBJECTIVES

The objective of this study is to detect and identify OXA-48-like and CTX-M-15 enzymes using mass spectrometry, and to subsequently develop a method for detection of both enzyme types in combination with liquid chromatography.

METHODS

Cells grown in either broth or on agar were harvested, lysed, and, in some cases buffer-exchanged. Lysates produced from bacterial cells were separated and analyzed via liquid chromatography with mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS/MS).

RESULTS

The intact proteins of OXA-48, OXA-181, and OXA-232 (collectively OXA-48-like herein) and CTX-M-15 were characterized and detected. Acceptance criteria based on sequence-informative fragments from each protein group were established as confirmatory markers for the presence of the protein(s). A total of 25 isolates were successfully tested for OXA-48 like (2), CTX-M-15 (3), or expression of both (7) enzymes. Thirteen isolates served as negative controls.

CONCLUSIONS

Here we present a method for the direct and independent detection of both OXA-48-like carbapenemases and CTX-M-15 β-lactamases using LC-MS/MS. The added sensitivity of MS/MS allows for simultaneous detection of at least two co-eluting, co-isolated and co-fragmented proteins from a single mass spectrum.

Comparison of the Xpert Carba-R and NG-Test CARBA5 for the detection of carbapenemases in an IMP-type carbapenemase endemic region in Japan

INTRODUCTION

The real-time PCR assay Xpert Carba-R and the lateral flow immunoassay NG-Test CARBA5 were developed to detect 5 types of carbapenemase genes (bla_IMP, bla_KPC, bla_VIM, bla_OXA-48, and bla_NDM).

METHODS

We compared the diagnostic performance, turn-around time, and cost of these assays. Carbapenemase genes were defined using the Carba NP test, modified Carbapenem Inactivation Methods (mCIM), multiplex PCR, and whole-genome sequencing. We included clinical Enterobacterales isolates (n = 36) and nonfermenting gram-negative bacilli isolates (n = 17) collected from 16 acute-care hospitals in the Kinki region of Japan.

RESULTS

Twenty-six of these 53 isolates were positive according to both of the Carba NP test and mCIM and, contained the following carbapenemase genes: bla_IMP-1 (n = 3), bla_IMP-6 (n = 1), bla_IMP-19 (n = 12), bla_IMP-26 (n = 1), bla_IMP-41 (n = 2), bla_IMP-66 (n = 2), bla_NDM-1 (n = 3), and bla_VIM-2 (n = 2). All of the remaining 27 isolates were negative according to the Carba NP test, mCIM, and multiplex PCR. The specificities of both assays were 100%. The sensitivity of the Xpert Carba-R assay was as low as 53.8% and that of the NG-Test CARBA5 was 92.3% because the former failed to detect all isolates with bla_IMP-19 (n = 12) and the latter failed to detect isolates with bla_IMP-66 (n = 2). Both assays can easily be performed in less than 5 min.

CONCLUSIONS

The NG-Test CARBA5 assay was superior with regard to assay time and cost per sample. We propose the use of the NG-Test CARBA5 assay in clinical laboratories where IMP-type carbapenemases are endemic.

Comparative Evaluation of Five Assays for Detection of Carbapenemases with a Proposed Scheme for Their Precise Application

The escalating problem of the dissemination of carbapenemase-producing bacteria (CPB) has gained worldwide attention. The prompt diagnosis of CPB and precise identification of carbapenemases are imperative to enable specific antibiotic therapy and control the spread of these bacteria. The present study was designed to assess the performance of five important assays for the detection of carbapenemases. The modified carbapenem inactivation method (mCIM), CARBA-5, GeneXpert Carba-R, BD MAX Check-Points CPO, and GeneFields CPE assays were evaluated with an international collection of 159 bacterial isolates, including 93 CPB and 66 non-CPB isolates. The overall accuracy/sensitivity/specificity for carbapenemase detection were 100% (95% CI, 97.7%-100%)/100% (95% CI, 96.1%-100%)/100% (95% CI, 94.6%-100%) for mCIM, 98.7% (95% CI, 95.5%-99.9%)/97.9% (95% CI, 92.5%-99.7%)/100% (95% CI, 94.6%-100%) for CARBA-5, 96.9% (95% CI, 92.8%-99%)/95.7% (95% CI, 89.4%-98.8%)/98.5% (95% CI, 91.8%-99.9%) for GeneXpert Carba-R, 94.3% (95% CI, 89.5%-97.4%)/90.3% (95% CI, 82.4%-95.5%)/100% (95% CI, 94.6%-100%) for BD MAX Check-Points CPO, and 86.2% (95% CI, 79.8%-91.1%)/77.4% (95% CI, 67.6%-85.5%)/98.5% (95% CI, 91.8%-100%) for GeneFields CPE. Interestingly, mCIM and CARBA-5 assays showed 100% accuracy/sensitivity/specificity for detection of the target genes. Furthermore, all the other assays showed comparable high accuracy (96.9% to 100%), sensitivity (100%), and specificity (96.4% to 100%) for the detection of the target genes. On the basis of these results, a new scheme was proposed for their efficient application. These results confirmed the high sensitivity of the evaluated assays, and the proposed scheme is reliable and improves the overall sensitivity and specificity of the assays.

Antibacterial Mechanism of Vanillic Acid on Physiological, Morphological, and Biofilm Properties of Carbapenem-Resistant Enterobacter hormaechei

ABSTRACT

Many studies have evaluated the antimicrobial activity of natural products against various microorganisms, but to our knowledge there have been no studies of the possible use of natural products for their antimicrobial activity against Enterobacter hormaechei. In this study, we investigated vanillic acid (VA) for its antimicrobial activities and its modes of action against carbapenem-resistant E. hormaechei (CREH). The MIC of VA against CREH was determined by the agar diffusion method. The antibacterial action of VA against CREH was elucidated by measuring variations in intracellular ATP concentration, intracellular pH, membrane potential, and cell morphology. Moreover, the efficacy of VA against biofilm formation and VA damage to CREH cells embedded in biofilms were further explored. Our results show that VA was effective against CREH with a MIC of 0.8 mg/mL. VA could rupture the cell membrane integrity of CREH, as measured by a decrease of intracellular ATP, pH, and membrane potential, along with distinctive alternations in cell morphology. In addition, VA exerted a remarkable inhibitory effect on the biofilm formation of CREH and also killed CREH cells within biofilms. These findings show that VA has a potent antibacterial and antibiofilm activity against CREH and, hence, has the potential to be used clinically as a novel candidate agent to treat CREH infections and in the food industry as a food preservative and surface disinfectant.

HIGHLIGHTS

Rapid Carbapenemase Detection With Xpert Carba-R V2 Directly On Positive Blood Vials

The rapid detection of carbapenemase allows implementation of infection control measures and adaptation of antibiotic therapy. We evaluated the performances of the Xpert Carba-R V2^® assay for the direct detection and identification of carbapenemase on positive blood cultures. We focused our evaluation on its detection capacity and on the risks of interference due to the patient’s blood. Isolates of several variants of OXA-48-like (n=10), KPC (n=10), NDM (n=11), VIM (n=7), IMP-1 (n=1) carbapenemases and 14 non carbapenemase-producing Enterobacteriaceae were tested. For each isolate (n=53), an aerobic vial was seeded, and incubated in Bactec Fx (Becton Dickinson^®) automate. When positive, the Xpert^® Carba-R-V2 assay was assessed for carbapenemase detection using 40 µl aliquot. Reproducibility tests were performed on a subset of 23 isolates using aerobic and anaerobic vials. Longer incubation time was also evaluated on 6 isolates. A complementary prospective study in real-time testing of patient-derived clinical samples on 20 additional positive blood vials with Gram negative bacilli on direct examination was performed. Perfect sensitivity and specificity (100%) were observed regardless of the carbapenemase type, the blood vials used and the time of incubation. Xpert^® Carba-R-V2 assay is suitable for the rapid detection of the main carbapenemase genes directly on positive blood vials. Its performances and rapid time analysis allow its use in routine to guide therapeutic choices and to implement infection control measures.

Rapid and Easy Detection of Carbapenemases in Enterobacterales in the Routine Laboratory Using the New GenePOC Carba/Revogene Carba C Assay

The novel, real-time PCR-based GenePOC Carba assay on the microfluidic revogene platform (GenePOC, Québec, Canada; now Meridian Bioscience, Cincinnati, OH, USA) was recently designed for the detection of bla _KPC, bla _NDM, bla _VIM, bla _OXA-48-like, and bla _IMP The goals of this study were to evaluate the performance of this assay, to assess its suitability for the routine microbiology laboratory, and to compare it to the Xpert Carba-R assay for the detection of carbapenemase-producing Enterobacterales (CPE) strains. The Xpert Carba-R assay (Cepheid) and the GenePOC Carba assay were challenged with a collection of 176 clinical Enterobacterales isolates. The collection included 133 CPE strains producing a total of 139 carbapenemases, including VIM (n = 48), OXA-48-like (n = 40), NDM (n = 29), KPC (n = 13), and IMP (n = 9). Six isolates produced two different carbapenemases, and 43 carbapenemase-negative isolates were included as negative controls. The overall sensitivity for carbapenemase detection was 96.4% (95% confidence interval [CI], 91.9% to 98.5%) for the Xpert Carba-R assay and 100% (95% CI, 97.3% to 100%) for the GenePOC assay. The four most common carbapenemases (NDM, KPC, OXA-48-like, and VIM) were detected with a sensitivity of 100% (95% CI, 97.1% to 100%) by the two tests, with all double carbapenemase producers being correctly detected by both assays. The sensitivity of the Xpert Carba-R assay for IMP was 44.4% (95% CI, 18.9% to 73.3%), while that of the GenePOC assay was 100% (95% CI, 70.1% to 100%). The specificity of both assays was 100% (95% CI, 91.8% to 100%). The GenePOC Carba assay showed excellent sensitivity and specificity for the five most common carbapenemases, including IMP variants. Its simplicity and short turnaround time make it suitable for use in the routine microbiology laboratory for CPE detection.

Multidrug-resistant Gram-negative bacterial infections in solid organ transplant recipients-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of infections due to multidrug-resistant (MDR) Gram-negative bacilli in the pre- and post-transplant period. MDR Gram-negative bacilli, including carbapenem-resistant Enterobacteriaceae, MDR Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii, remain a threat to successful organ transplantation. Clinicians now have access to at least five novel agents with activity against some of these organisms, with others in the advanced stages of clinical development. No agent, however, provides universal and predictable activity against any of these pathogens, and very little is available to treat infections with MDR nonfermenting Gram-negative bacilli including A baumannii. Despite advances, empiric antibiotics should be tailored to local microbiology and targeted regimens should be tailored to susceptibilities. Source control remains an important part of the therapeutic armamentarium. Morbidity and mortality associated with infections due to MDR Gram-negative organisms remain unacceptably high. Heightened infection control and antimicrobial stewardship initiatives are needed to prevent these infections, curtail their transmission, and limit the evolution of MDR Gram-negative pathogens, especially in the setting of organ transplantation.

Comparison of five methods for detection of carbapenemases in Enterobacterales with proposal of a new algorithm

OBJECTIVES

The aim of this study was to evaluate the performance of five different carbapenemase tests and to develop an algorithm which will permit the detection of most common and rare carbapenemases in routine microbiology laboratories.

METHODS

The immunochromatographic tests CARBA-5 (NG), RESIST-4 O.K.N.V. (Coris), the colorimetric β-CARBA (BioRad), a newly developed carbapenem-inactivation method (CIM) supplemented with zinc (zCIM), and the Xpert Carba-R (Cepheid) were challenged with a collection of 189 molecularly characterized Enterobacterales isolates, including 146 carbapenemase producers (CPE): VIM (n = 48), OXA-48-like (n = 40), NDM (n = 29), KPC (n = 13), IMI (n = 9), IMP (n = 9), OXA-58 (n = 2), and GES (n = 2).

RESULTS

The overall sensitivity/specificity values for the five carbapenemase detection tests were 84.2% (CI 77.6-89.2%)/100% (CI 91.8-100%) for RESIST-4, 88.2% (CI 82.1-92.4%)/100% (CI 91.8-100%) for CARBA-5, 88.2% (CI 82.1-92.4%)/100% (CI 91.8-100%) for Xpert Carba-R, 73.7% (CI 66.2-80.0%)/100% (CI 93.4-99.0%) for β-CARBA, and 97.4% (CI 87.9-99.6%)/97.7% (CI 87.9-99.6%) for zCIM. The four common carbapenemases (KPC, OXA-48-like, NDM, and VIM) were detected with ≥97.6% sensitivity by all tests except for β-CARBA (76.6% (CI 68.4-83.2%)). IMI and GES were only detected by zCIM (sensitivity 90.9% (CI 62.3-98.4%)). Based on these results a new algorithm was developed, consisting of an immunochromatographic assay as the first test followed by zCIM, which allows detection of 99.3% of all carbapenemases assessed.

CONCLUSIONS

Except for β-CARBA, all methods showed excellent sensitivity/specificity for the detection of the four most frequent carbapenemases. With the new algorithm, rare variants can also be detected. It is rapid, simple, and inexpensive and can be performed in any microbiology laboratory, as no PCR equipment is required.

Direct Detection of Carbapenem-Resistant Organisms from Environmental Samples Using the GeneXpert Molecular Diagnostic System

Use of the Carba-R assay for detection of carbapenem-resistant Gram-negative organisms (CROs) can provide data for implementation of a rapid infection control response to minimize the spread of CROs in the health care setting.

In this pilot study, traditional culture and PCR methods were compared to the Cepheid GeneXpert IV molecular diagnostic system with the Xpert Carba-R assay (Carba-R assay) for detection of carbapenem resistance genes in primary environmental samples collected during a health care-related outbreak. Overall, traditional culture-dependent PCR and the Carba-R assay demonstrated 75% agreement. The Carba-R assay detected carbapenemase genes in five additional samples and in two samples that had additional genes when compared to culture-dependent PCR. The Carba-R assay could be useful for prioritizing further testing of environmental samples during health care-related outbreaks.

IMPORTANCE Use of the Carba-R assay for detection of carbapenem-resistant Gram-negative organisms (CROs) can provide data for implementation of a rapid infection control response to minimize the spread of CROs in the health care setting.

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

This multicenter study evaluated the performance of the Cepheid Xpert Carba-R assay, a qualitative PCR test designed for the rapid detection of bla_KPC, bla_NDM, bla_VIM, bla_IMP, and bla_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 Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii 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.

Environmental pollution with antimicrobial agents from bulk drug manufacturing industries in Hyderabad, South India, is associated with dissemination of extended-spectrum beta-lactamase and carbapenemase-producing pathogens

PURPOSE

High antibiotic and antifungal concentrations in wastewater from anti-infective drug production may exert selection pressure for multidrug-resistant (MDR) pathogens. We investigated the environmental presence of active pharmaceutical ingredients and their association with MDR Gram-negative bacteria in Hyderabad, South India, a major production area for the global bulk drug market.

METHODS

From Nov 19 to 28, 2016, water samples were collected from the direct environment of bulk drug manufacturing facilities, the vicinity of two sewage treatment plants, the Musi River, and habitats in Hyderabad and nearby villages. Samples were analyzed for 25 anti-infective pharmaceuticals with liquid chromatography-tandem mass spectrometry and for MDR Gram-negative bacteria using chromogenic culture media. In addition, specimens were screened with PCR for bla _VIM, bla _KPC, bla _NDM, bla _IMP-1, and bla _OXA-48 resistance genes.

RESULTS

All environmental specimens from 28 different sampling sites were contaminated with antimicrobials. High concentrations of moxifloxacin, voriconazole, and fluconazole (up to 694.1, 2500, and 236,950 µg/L, respectively) as well as increased concentrations of eight other antibiotics were found in sewers in the Patancheru-Bollaram industrial area. Corresponding microbiological analyses revealed an extensive presence of extended-spectrum beta-lactamase and carbapenemase-producing Enterobacteriaceae and non-fermenters (carrying mainly bla _OXA-48, bla _NDM, and bla _KPC) in more than 95% of the samples.

CONCLUSIONS

Insufficient wastewater management by bulk drug manufacturing facilities leads to unprecedented contamination of water resources with antimicrobial pharmaceuticals, which seems to be associated with the selection and dissemination of carbapenemase-producing pathogens. The development and global spread of antimicrobial resistance present a major challenge for pharmaceutical producers and regulatory agencies.

Evaluation of Genotypic and Phenotypic Methods to Detect Carbapenemase Production in Gram-Negative Bacilli

BACKGROUND

Carbapenemase-producing gram-negative bacteria (CP-GNB) are an urgent and expanding public health threat. Rapid and accurate identification of these organisms facilitates infection prevention efforts in healthcare facilities. The objective of our study was to evaluate methods to detect and identify CP-GNB.

METHODS

We examined 189 carbapenem-resistant GNB(CR-GNB), including Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii complex, using 3 different methods: 2 methods to screen isolates of GNB for carbapenemase production [the carbapenem inactivation method (CIM) and 2 chromogenic agars] and a molecular method (Cepheid GeneXpert Carba-R) to identify the mechanism of carbapenem resistance and the associated resistance genes (bla_KPC, bla_NDM, bla_IMP, bla_OXA-48-like, and bla_VIM).

RESULTS

The CIM was a simple and inexpensive phenotypic screen to differentiate between CR-GNB and CP-GNB, with improved analytical performance characteristics and inter-reader correlation compared to the modified Hodge test. Both chromogenic agars evaluated (HardyCHROM CRE and chromID CARBA) were able to support growth of most of the organisms tested, including isolates possessing the bla_OXA-48-like gene. However, these media had a low analytical specificity for carbapenemase production, with breakthrough of CR-GNB that did not produce a carbapenemase. The Xpert Carba-R assay was rapid and easy to perform, and demonstrated 100% positive and negative agreement for characterization of genetic determinants of carbapenem resistance.

CONCLUSIONS

Screening by CIM followed by the Xpert Carba-R PCR is an accurate method for detecting and characterizing CP-GNB, including Enterobacteriaceae, P. aeruginosa, and A. baumannii complex.