Multicenter Evaluation of Rapid BACpro® II for the Accurate Identification of Microorganisms Directly from Blood Cultures Using MALDI-TOF MS.

Marina Oviaño,Guy Prod’Hom,Belén Rodríguez-Sánchez,Gilbert Greub,André Ingebretsen,Anne K Steffensen,Germán Bou,David Rodríguez-Temporal,Lidia Quiroga,Antony Croxatto

doi:10.3390/diagnostics11122251

Abstract

The identification of microorganisms directly from blood cultures using MALDI-TOF MS has been shown to be the most impacting application of this methodology. In this study, a novel commercial method was evaluated in four clinical microbiology laboratories. Positive blood culture samples (n = 801) were processed using a rapid BACpro® II kit and then compared with the routine gold standard. A subset of monomicrobial BCs (n = 560) were analyzed in parallel with a Sepsityper® Kit (Bruker Daltonics, Bremen, Germany) and compared with the rapid BACpro® II kit. In addition, this kit was also compared with two different in-house methods. Overall, 80.0% of the monomicrobial isolates (609/761; 95% CI 71.5–88.5) were correctly identified by the rapid BACpro® II kit at the species level (92.3% of the Gram negative and 72.4% of the Gram positive bacteria). The comparison with the Sepsityper® Kit showed that the rapid BACpro® II kit generated higher rates of correct species-level identification for all categories (p > 0.0001), except for yeasts identified with score values > 1.7. It also proved superior to the ammonium chloride method (p > 0.0001), but the differential centrifugation method allowed for higher rates of correct identification for Gram negative bacteria (p > 0.1). The percentage of accurate species-level identification of Gram positive bacteria was particularly noteworthy in comparison with other commercial and in-house methods.

Highlights

The rapid identification of microorganisms causing bloodstream infections (BSI) is one of the most impactful applications of Matrix Assisted Laser Desorption/IonizationTime of Flight Mass Spectrometry (MALDI-TOF MS) in clinical microbiology [1,2]
801 consecutive, positive blood cultures (BCs) were collected in the four participating laboratories, and microorganisms present in these cultures were identified by MALDI-TOF MS after sample pre-processing using the rapid BACpro® II kit
We identified 80.0% of the isolates correctly at the species level with score values ≥2.0, and 94.4% correctly at the genus level with score values ≥1.7

Summary

Introduction

The rapid identification of microorganisms causing bloodstream infections (BSI) is one of the most impactful applications of Matrix Assisted Laser Desorption/IonizationTime of Flight Mass Spectrometry (MALDI-TOF MS) in clinical microbiology [1,2]. This technology has demonstrated the timely and accurate identification of a wide variety of microorganisms directly from positive blood cultures (BCs) and has the added benefit of being inexpensive and efficient [3]. Other studies have reported short-incubations of BC broth on agar plates (for 2 to 6 h) prior to MALDI-TOF MS identification from the thin layer of microorganisms grown on the surface of the plate [10]. This proceeding has allowed for the successful identification of bacteria and has even helped overcome some of the limitations of MALDI-TOF MS: the accurate identification of more than one pathogen in polymicrobial infections and reliable identification of Gram positive microorganisms [11]

Methods

Results

Discussion

Conclusion