Bacteriology
Direct identification of bacteria in positive blood cultures: comparison of two rapid methods, FilmArray and mass spectrometry,☆☆

https://doi.org/10.1016/j.diagmicrobio.2014.03.014Get rights and content

Abstract

We evaluated the accuracy and performance of the FilmArray Direct from Positive Blood Culture system (BCID) (BioFire Diagnostics, Salt Lake City, UT, USA) and the VITEK Mass Spectrometry System (Vitek MS; bioMerieux, Durham, NC, USA) to identify bacterial isolates from 161 positive blood culture bottles. The BCID uses multiplex PCR to identify 90–95% of common isolates to the genus or species/complex level as well as mecA, Van A/B, and blaKPC genes in approximately 1 hour. Of 151 monomicrobic isolates, the FilmArray correctly identified 48/49 (98%) to the genus and 84/84 (100%) to the species/complex level, while 18/151 (12%) gave no identification, as expected from the database. Mass spectrometry correctly identified 142/151 (94%) monomicrobic cultures to the genus level, 137/151 (91%) to the species level, with only 8/151(5%) giving no identification. Although mass spectrometry has a much larger database, the filtration system was cumbersome in contrast to the 3–5 minutes hands-on-time for the BCID.

Introduction

The need for rapid antibiotic treatment of sepsis is well recognized, and the time to implementation of appropriate antibiotic therapy is critical in improving the outcome of sepsis Leibovici et al. (1998), Kumar (2009), Kollef et al. (1999). Recently, several methods have been developed to identify pathogens and some resistance genes directly from positive blood culture bottles, which can shorten the time for final identification and susceptibility by as much as 1–2 days. In addition to the Verigene system (Nanosphere, Northbrook, IL, USA) Buchan et al. (2013), Wojewoda et al. (2013), Samuel et al. (2013), the FilmArray Direct from Positive Blood Culture system (BCID) (BioFire Diagnostics, Salt Lake City, UT, USA) Blaschke et al. (2012), Altun et al. (2013) carries out a multiplex PCR that identifies approximately 90–95% of the most common gram-negative and gram-positive isolates to the genus or species level as well as mecA, van A/B, and blaKPC genes in approximately 1 hour. In these studies, the FilmArray BCID correctly identified 91–95% of all isolates in positive monomicrobial blood cultures. Mass spectrometry has become increasingly available for the routine identification of bacteria, and several groups have reported its use to identify bacteria directly from positive blood culture bottles (Fothergill et al., 2013, Jamal et al., 2013, Lagace-Wiens et al., 2012, March-Rossello et al., 2013). Sensitivity in these studies has ranged from 75% to 98% for monomicrobic positive blood cultures. Clinical microbiology laboratories under pressure to control or reduce costs while providing more rapid, cost-effective service may need to choose between these competing technologies. We compared with FilmArray BCID with the VITEK Mass Spectrometry System (VITEK MS; bioMerieux, Durham, NC, USA) for the identification of 161 positive BacTec blood culture bottles.

Section snippets

Study design

The study design was a direct comparison of the BCID with the Vitek MS using fluid from the same positive blood culture bottle tested at the same time by both methods. Fluid from the positive bottle was used to inoculate the FilmArray BCID, and while that was being processed in the instrument, the blood culture fluid was prepared for mass spectrometry as described below. Between October 2012 and May 2013, 161 positive blood cultures in the Shands Hospital, University of Florida, Gainesville,

Results

Of the 161 positive blood culture bottles, 151 were monomicrobic and 10 were polymicrobic. Table 1 shows a complete list of the monomicrobic isolates identified by each system. Table 2 shows the polymicrobic isolates.

As shown in Table 3, a total of 132/133 (99%) of isolates that were in the FilmArray panel were identified correctly to the genus and/or species level. For those organisms that the FilmArray could identify to the species or species/complex level, 84/84 (100%) were correctly

Discussion

The ability to report identification and susceptibility data directly from positive blood cultures shortly after they signal positive growth is of great value in reducing the time to appropriate antibiotic treatment. The FilmArray identified 99% of the isolates and resistance genes expected based on the capabilities described by the manufacturer and identified 88.1% of all monomicrobic blood cultures in the study. Mass spectrometry identified 142/151 (94%) monomicrobic cultures to the genus

Funding

This work was supported in part by a research grant from BioFire Diagnostics, Inc.

Potential conflicts of interest

K. H. R. has received funding and honoraria from BioFire Diagnostics, Inc.

References (21)

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Supported in part by a grant from BioFire Diagnostics, Inc., Salt Lake City, UT.

☆☆

Presented in part at the 113th Annual Meeting of the American Society for Microbiology, Denver, CO, May 18–21, 2013.

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