Gram-Positive Blood Culture*

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Literature Cited

"Evaluation of the Microarray‐Based Sample‐to‐Result Verigene BC‐GP Assay for Rapid Detection of Gram‐Positive Bacteria and Resistance Determinants Directly from Positive Blood Cultures"
18 September 2011
Full data
Buchan BW, Mackey T, Cahak C, Couillard H, Marla S, Raich T, Sauer L, Jannetto PJ, Ledeboer NA
Abstract
Background: Bacteremia and sepsis result in high morbidity and mortality. A majority of positive blood cultures are due to gram‐ positive bacteria including Staphyloccocus, Enterococcus, Streptococcus, and Micrococcus. Some of these organisms are associated with serious infection, while others are skin flora associated with lines or improperly collected specimens. Early identification of the organism and appropriate antibiotic treatment is critical to management of the infection and improving patient outcome.
Methods: Sixty positive blood cultures containing gram‐positive bacteria were analyzed using the Verigene Gram Positive Blood Culture (BC‐GP) Assay (Nanosphere, Northbrook, IL). Testing of cultures was done within 8h of positivity. The BC‐GP detects 13 bacterial targets including Staphylococcus, Streptococcus, Enterococcus, Micrococcus and Listeria species. The resistance determinants mecA (oxacillin) and vanA/B (vancomycin) are also detected.
Results: Three cultures contained organisms not on the BC‐GP panel (Bacillus, Lactobacillus), and were resulted as “Not Detected”. Compared to biochemical identification, 55 of 57 positive blood cultures were concordant with BC‐GP results. One culture contained viridans group Streptococci by biochemical identification, which was discordant with the BC‐GP result (S. pneumoniae). In 4 of 5 cultures containing two organisms the BC‐GP correctly identified both organisms; in one culture the BC‐GP identified 1 of 2 organisms present. This translates to a combined sensitivity of 98.4%. The BC‐GP predicted oxacillin resistance in 34 Staphylococcus spp. (18 mecA +) and vancomycin resistance in 10 Enterococcus spp. (6 vanA +) for 100% sensitivity and specificity.
Conclusions: The BC‐GP assay identifies 13 gram‐positive targets and 2 resistance markers directly from positive blood cultures. The BC‐GP requires only 350μl of specimen and results are available within 2.5 hours of blood culture positivity.
Buchan et al ICAAC 2011 Poster.pdf
"Rapid detection of Gram-positive bacteria and resistance determinants directly from positive blood cultures using the microarray-based sample-to-result Verigene BC-GP assay"
22rd European Congress of Clinical Microbiology and Infectious Diseases
02 April 2012
Full data
Buchan BW, Mackey TA, Jannetto PJ, Ledeboer NA
Abstract
Objectives: Gram-positive bacteria constitute the majority of positive blood cultures. Some of these organisms are associated with serious infection, while others are skin flora associated with lines or improperly collected specimens. Early identification of the organism and appropriate antibiotic treatment are critical to management of the infection and improving patient outcome. We evaluate the microarray-based Verigene Gram-Positive Blood Culture (BC-GP) Assay (Nanosphere, Northbrook, IL, USA) for detection of bacteria directly from positive blood cultures. 
Methods: A total of 119 positive blood cultures containing gram-positive bacteria were analyzed using the BC-GP within 12 h of culture positivity. Results were compared to routine biochemical testing as the gold standard. The BC-GP detects 13 bacterial targets including Staphylococcus, Streptococcus, Enterococcus, Micrococcus and Listeria species. The resistance determinants mecA (oxacillin) and vanA/vanB (vancomycin) are also detected. 
Results: Among 114 monomicrobial cultures, the BC-GP was 100% sensitive in detection of Staphylococcus spp (n=83), S. aureus (n=35), S. lugdunensis (n=1), Streptococcus spp (n=10), S. agalactiae (n=5), Micrococcus spp (n=5), and E. faecalis (n=9). BC-GP was 93.9% specific for detection of S. epidermidis (n=33) and 75.0% sensitive for E. faecium. Three cultures contained organisms not on the BC-GP panel (Kocuria, Granulicatella), and were resulted as “Not Detected”. In 1 of 4 cultures containing two organisms the BC-GP correctly identified both organisms (S. aureus, S. epidermidis); the remaining 3 cultures contained S. epidermidis and S. hominis and were resulted as S. epidermidis. The BC-GP correctly predicted oxacillin resistance in 100% (34/34) S. aureus or S. epidermidis (mecA +) and vancomycin resistance in 100% (2/2) Enterococcus spp. (vanA +). A reproducibility panel of 20 strains was tested 20 times immediately following culture positivity or 8 h after positivity. The call rate was 97% (388/400) at initial positivity and 96% (384/400) 8 h after positivity. All samples failing to generate a result at both time points successfully returned an accurate result following a single retest (final call rate 100%). 
Conclusions: The BC-GP assay identifies 13 gram-positive targets and 3 resistance markers directly from positive blood cultures. The BC-GP requires only 350 µl of specimen and results are available within 2.5 h of blood culture positivity.
Link to Abstract - ECCMID 2012
ECCMID 2012 Poster
"Performance of the Nanosphere Verigene BC-GP test for rapid detection of Gram-positive bacteria and resistance determinants directly from positive blood cultures"
22rd European Congress of Clinical Microbiology and Infectious Diseases
01 April 2012
Full data
Tormo N, Medina R, Ocete MR, et al
Abstract
Objective: To compare the preliminary results obtained with the microarray-based Nanosphere´s Verigene Blood Culture – Gram Positive (BC-GP) test, a new tool for rapid detection of gram-positive pathogens in blood stream infections (BSI) in the setting of a European evaluation study of both the assay and the Verigene® System equipment, with the conventional method performed currently in our laboratory. 
Methods: We tested 65 positive blood cultures (BD BACTECTM). After Gram staining, we immediately performed the Verigene BC-GP assay with 350 µl of blood from the BC vial. Results were obtained in 2.5 h. We proceded simultaneously to quantitative subculture in common agar plates and direct disk-diffusion susceptibility testing. After overnight incubation, we got preliminary results on susceptibility and presumptive identification of bacteria, and performed automated biochemical identification and microdilution antibiotic testing with MicroScan® Gram positive Combo 32 panels (Siemens), that were again incubated overnight. Definitive results with conventional culture method took 48 h in being released. 
Results: Sixty-four (97%) up to 66 (one blood culture had two different isolates) initial identification Verigene results were concordant with biochemical testing. One initial negative Verigene result was retested and then coincided with the conventional method, so in 98.5% of cases results were consistent between both methods. The other initial negative Verigene result was not retested and a CoNS (S. hominis) was recovered in plate culture, but it had the lowest count in CFU/mL of the series, i.e. 7.10E5 CFU/mL vs. >=1.10E6 CFU/mL. Two mixed infections were tested and Verigene results were concordant with culture: one consisted of Acinetobacter baumanii and S. haemolyticus, and Verigene detected “Staphylococcus sp” with no other signal; the other was composed of S. epidermidis and S. mitis and both were correctly identified by Verigene. In terms of Verigene resistance determinants’ detection, there was no failure compared to culture. 
Conclusion: Preliminary results with the new Verigene BC-GP test are good, with 100% specificity and 98.5% sensitivity in bacterial identification and 100% specificity and sensitivity in important resistance determinants’ detection. It´s a new tool for diagnosis of gram positive’s BSI to keep under consideration because significant results can be discriminated and reported at least 24 hours before current conventional culture method.
Link to Abstract - ECCMID 2012
ECCMID 2012 Poster
"Evaluation of the Verigene Gram-Positive Blood Culture Test (BC-GP)"
American Society of Microbiology 2012 Meeting
18 June 2012
Full data
Anderson C, Kaul K, Voss B, Thomson RB
Abstract
Background: Rapid detection, identification and antimicrobial testing of blood borne pathogens improve antimicrobial stewardship and patient care. The Verigene BC-GP is a multiplexed, automated nucleic acid test for the direct identification from positive blood culture broth of genus, species and genetic resistance determinants for a panel of common Gram-positive bacteria. We prospectively evaluated the Verigene BC-GP Test (Nanosphere) using positive patient blood cultures.
Methods: Positive BACTEC plus aerobic/F blood culture bottles with a direct Gram stain showing Gram positive organisms were enrolled. Positive cultures were limited to one per patient and were processed using the Verigene System within 12 h of BACTEC detection. Phenotypic identification using conventional biochemical testing established accepted identification. The Verigene System is an automated random access instrument that requires 5 min of hands-on and 2.5 h of run time. The BC-GP Test, which runs on the Verigene System, can identify Staphylococcus spp., S.aureus, S. epidermidis, S. lugdunensis, Streptococcus spp., S. pneumoniae, S. pyogenes, S. agalactiae, S. anginosus group, E. faecalis, E. faecium, Micrococcus spp., and Listeria spp,, in addition to methicillin resistance marker mecA in S. aureus and S. epidermidis, and vancomycin resistance markers vanA and vanB in E. faecalis and E. faecium. Conventional identification and BC-GP testing were performed by separate technologists in a blinded fashion.
Results: 136 Gram-positive bacteria were detected. 129/136 (95%) isolates included targets detected by BC-GP test. 126/129 isolates were correctly identified by BC-GP, including 31 S. aureus, 10 beta streps, 6 S. pneumoniae, 11 viridans streptococci, 8 enterococci and 2 Micrococcus spp. 9/126 were correctly identified when repeated following an error message during the first run. 2 viridans streptococci and 1 E. faecium were not detected by BC-GP, but should have been.
Discussion: The Verigene BC-GP Test accurately and rapidly detects most Grampositive pathogens and resistance mechanisms directly from positive blood culture bottles in less than 3 hours. The automated Verigene System allows 24/7 processing by laboratory technicians. Results are available 1-2 d sooner than those provided by conventional testing.
 
Link to ASM 2012 Final Program
Anderson Poster ASM 2012.pdf