Evaluation of the Nanosphere Verigene BC-GN Assay for Direct Identification of Gram-Negative Bacilli and Antibiotic Resistance Markers from Positive Blood Cultures and Potential Impact for More-Rapid Antibiotic Interventions

Abstract

The Verigene BC-GN assay correctly identified all 51 Gram-negative bacilli (GNB) from positive blood cultures and all 14 carbapenemase enzymes tested. The assay gave organism identification (ID) results an average of 24 h faster compared to conventional identifications. Medical management could have been modified for 31.8% of patients an average 33 h sooner. In conclusion, the BC-GN assay is a very accurate, rapid assay which would allow for more-immediate medical management decisions in patients with bacteremia from GNB. Early and appropriate therapeutic interventions have been shown to reduce mortality associated with hospital-acquired bloodstream infections (BSIs) (1, 2). The clinical decision of whether to broaden antimicrobial coverage from that of initial empirical therapy or to narrow coverage is supported by knowledge of the organism identification (ID) and antimicrobial susceptibility testing (AST) profile. Since the 1970s, the prevalence of Gram-positive pathogens causing BSIs has typically exceeded that of Gram-negative bacilli (GNB). However, in recent years, the incidence of BSIs caused by GNB has been increasing (3). Additionally, there has been a dramatic increase of antibiotic resistance in GNB mediated by extended-spectrum ␤-lactamase (ESBL) and carbapenemase enzymes.The current workup of a positive blood culture includes Gram staining, plating to solid medium, spot testing for ID, and/or automated ID assays. This process can take up to 18 to 24 h for an ID result and up to an additional 24 h for AST results. The Verigene Gram-negative blood culture (BC-GN) assay (Nanosphere, Inc., Northfield, IL) is a FDA-approved, random-access, automated, multiplexed nucleic acid test for the rapid ID of the most common GNB (and selected resistance markers [RMs]) from blood cultures within 2 h of positivity (4). The assay will allow detection of the following organisms and RMs: Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter species, Citrobacter species, Proteus species, Acinetobacter species, Pseudomonas aeruginosa, CTX-M, KPC, NDM, VIM, IMP, and OXA. This study was undertaken with the following aims: (i) to determine the accuracy of this new assay for the ID of GNB and RM detection, (ii) to review turnaround times (TAT) for molecular ID compared to routine culture ID, and (iii) to ascertain whether/when medical management could have changed based on the BC-GN result in comparison to conventional methods.(This study was partially presented in poster form at the 113th General Meeting of the American Society for Microbiology, 2013.)Fifty-four consecutive inpatient positive blood cultures received from August 2013 to January 2014 that gave positive results between 7 a.m. and 11 p.m. were tested immediately by the BC-GN assay upon confirmation of GNB by Gram staining. All patients with positive blood cultures for Gram-negative bacilli detected during these hours were included in this analysis, but only the initial positive blood culture for each patient was included in the study. The re...

Clinical Uptake of Antimicrobial Stewardship Recommendations Following Nanosphere Verigene Blood Culture Gram-Negative Reporting

“…Hill et al (10) evaluated the performance of the Verigene BC-GN assay and potential impact of rapid antibiotic interventions in 54 patients. BC-GN identifi ed the organism approximately 24 hours faster than conventional methods.…”

“…Rapid identifi cation of GN bacteremia and key susceptibility markers can lead to many benefi ts, such as earlier deescalation of empiric therapy and switch to appropriate targeted antimicrobials that can lead to better patient outcomes, decreased length of hospital stay, and decreased overall hospital costs (9)(10)(11)(12). Th e Verigene BC-GN assay has two major advantages favoring its routine use: a random-access format with very limited handson time and the ability to rapidly provide clinically actionable therapeutic information to physicians.…”

Carbapenem-resistant Enterobacteriaceae in special populations: Solid organ transplant recipients, stem cell transplant recipients, and patients with hematologic malignancies

“…Two real-time, multiplex polymerase chain reaction systems have recently been approved in the US and can identify carbapenemase genes within 2 hours of blood culture positivity. [101][102][103] Implementation of these tools can decrease the time from blood culture collection until detection of CRE from 3 d to less than 24 hours. Furthermore, these systems also allow clinicians to de-escalate therapy when appropriate and avoid the attendant toxicities of CREactive agents.…”

Preliminary Evaluation of the Research-Use-Only (RUO) iCubate iC-GPC Assay for Identification of Select Gram-Positive Bacteria and Their Resistance Determinants in Blood Culture Broths

“…These methods include peptide nucleic acid fluorescence in situ hybridization (PNA-FISH), matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and real-time PCR (RT-PCR) or microarray-based molecular tests (1-10). The ability to reliably identify a specific bacterium or yeast present in a positive blood culture within 1 to 3 h of culture positivity using these methods has resulted in significant reductions in time to effective antimicrobial therapy, length of hospital/intensive care unit (ICU) stay, 30-day mortality, and cost of care (6,7,(11)(12)(13). Importantly, while organism identification alone can provide some benefit, the most significant benefits are achieved when the presence of resistance markers, such as mecA, vanA, or carbapenemases, is identified concomitantly (11,12,(14)(15)(16).…”

“…The ability to reliably identify a specific bacterium or yeast present in a positive blood culture within 1 to 3 h of culture positivity using these methods has resulted in significant reductions in time to effective antimicrobial therapy, length of hospital/intensive care unit (ICU) stay, 30-day mortality, and cost of care (6,7,(11)(12)(13). Importantly, while organism identification alone can provide some benefit, the most significant benefits are achieved when the presence of resistance markers, such as mecA, vanA, or carbapenemases, is identified concomitantly (11,12,(14)(15)(16).The research-use-only (RUO) iC-GPC assay (iCubate, Huntsville, AL) is a molecular target amplification assay capable of detecting and identifying Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Enterococcus faecalis, and Enterococcus faecium as well as the genetic resistance determinants mecA, vanA, and vanB directly from positive blood culture broths. The system consists of an automated processor (iC-Processor), a reader (iC-Reader), and single-use, closed-system test cassettes.…”