Development of a Treatment Algorithm for Streptococci and Enterococci from Positive Blood Cultures Identified with the Verigene Gram-Positive Blood Culture Assay

Abstract

Bloodstream infections (BSI) are a leading cause of morbidity and mortality. In 2009, BSI were the cause of nearly 36,000 deaths in the United States (1). Health care-associated BSI are a major contributor to these statistics, being associated with nearly 75,000 infections a year with a mortality rate of approximately 25% (2). Enterococci are the third leading cause of health careassociated BSI (3), and inappropriate antimicrobial therapy has been shown to be an independent risk factor for the increased mortality of BSI (4). The Nanosphere Verigene Gram-positive blood culture (BC-GP) assay (Nanosphere, Northbrook, IL) is an on-demand FDA-cleared test for the identification of 15 targets from positive blood culture bottles. Previous studies have shown this assay to be an effective method for determining the identity of Gram-positive organisms, showing 92 to 95% overall concordance for organism identification (5, 6); however, the implementation of an algorithm for treatment based on BC-GP test results has not been proposed. The current work focuses on the performance of the assay specifically in cultures where streptococci and enterococci are suspected based on the primary Gram stain and on the algorithm we have developed for treatment based on the BC-GP results.We first performed an evaluation of the BC-GP assay on the Nanosphere Verigene system. Routine blood cultures were collected using FAN aerobic (FA), pediatric FAN (PF), and standard anaerobic (SA) bottles and subsequently incubated on the BacT/ Alert (bioMérieux, Durham, NC) system. Positive blood cultures were Gram stained, plated onto solid medium, and stored upright at 35°C for up to 5 days. Subcultures were evaluated according to standard laboratory protocols, and organisms were identified using a combination of morphological and phenotypic methods as well as matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (Vitek MS; bioMérieux). Notably, the Vitek MS accurately distinguishes between Streptococcus pneumoniae and Streptococcus mitis/Streptococcus oralis (7). Positive blood cultures with a Gram stain of Gram-positive cocci in pairs and/or chains were further evaluated with the BC-GP assay according to the manufacturer's recommendations. The BC-GP targets analyzed include Enterococcus faecalis, Enterococcus faecium, Streptococcus spp., Streptococcus agalactiae, Streptococcus anginosus group, S. pneumoniae, Streptococcus pyogenes, and the resistance determinants vanA and vanB.Seventy-eight consecutive positive blood cultures from 74 patients with an initial Gram stain result containing Gram-positive cocci in pairs and/or chains were evaluated with the BC-GP assay, of which 72 had at least one target detected. Of the six cultures for which no target was detected, three grew organisms (Acinetobacter sp., Atopobium sp., B. cereus group) for which the assay does not target, and two grew Streptococcus vestibularis, which has not been evaluated by the manufacturer according to the package insert. The remaining negative BC...

Identification of Gram-Negative Bacteria and Genetic Resistance Determinants from Positive Blood Culture Broths by Use of the Verigene Gram-Negative Blood Culture Multiplex Microarray-Based Molecular Assay

“…These include fluorescence in situ hybridization (FISH), matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and nucleic acid amplification or detection assays (14)(15)(16)(17)(18)(19)(20)(21)(22)(23). While each approach has specific strengths and weaknesses, all have demonstrated their potential to positively impact key indicators, such as laboratory turnaround time, length of hospital stay, cost of care, and overall mortality associated with BSI.…”

“…Selection of the BC-GP or BC-GN assay is based on the primary Gram stain result of a positive blood culture broth. Several studies have reported on the performance of the BC-GP assay, which has a sensitivity ranging from 96% to 100% and Ͼ98% specificity for the majority of targets (18,21,24,25). The BC-GN assay has also been evaluated; however, studies to date have included Ͻ150 blood cultures or have included primarily simulated specimens (20,(26)(27)(28)(29)(30).…”

Potential Impact of a Microarray-Based Nucleic Acid Assay for Rapid Detection of Gram-Negative Bacteria and Resistance Markers in Positive Blood Cultures

“…Several papers have already evaluated the Verigene panel dedicated to Gram-positive bacteria (8)(9)(10)(11)(12), but this is the first one on the BC-GN test. To investigate its potential clinical usefulness, we evaluated the following parameters: (i) the concordance of identification and of antibiotic susceptibility data with those obtained with the traditional blood culture flowchart, (ii) the time to definitive results, and (iii) the impact of the BC-GN test results on ongoing empirical therapy, evidencing the rate of potential BC-GN-induced antibiotic changes.…”

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

“…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.…”

“…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).…”