Comparison of the Bruker MALDI-TOF mass spectrometry system and conventional phenotypic methods for identification of Gram-positive rods.

Claudia Barberis,María Soledad Ramírez,Carlos Vay,Marisa Almuzara,Angela Famiglietti,Olivier Join-Lambert,Holger Rohde

doi:10.1371/journal.pone.0106303

Abstract

In recent years, MALDI-TOF Mass Spectrometry (MS) method has emerged as a promising and a reliable tool for bacteria identification. In this study we compared Bruker MALDI-TOF MS and conventional phenotypic methods to identify a collection of 333 Gram-positive clinical isolates comprising 22 genera and 60 species. 16S rRNA sequencing was the reference molecular technique, and rpoB gene sequecing was used as a secondary gene target when 16Sr RNA did not allow species identification of Corynebacterium spp. We also investigate if score cut-offs values of ≥1,5 and ≥1,7 were accurate for genus and species-level identification using the Bruker system. Identification at species level was obtained for 92,49% of Gram-positive rods by MALDI-TOF MS compared to 85,89% by phenotypic method. Our data validates the score ≥1,5 for genus level and ≥1,7 for species-level identification in a large and diverse collection of Gram-positive rods. The present study has proved the accuracy of MALDI-TOF MS as an identification method in Gram-positive rods compared to currently used methods in routine laboratories.

Highlights

Corynebacterium spp. and other Gram-positive rods (GPR) are widespread throughout nature, being most of the species part of the normal skin flora of humans and animals [1]
Correct identification of Corynebacterium spp. and other GPR species is a very challenging task because it will help to identify the real source of infection and install the appropriate treatment for the infection
The aims of the present study were to compare the performance of MALDI-TOF Mass Spectrometry (MS) and conventional methods for the identification of GRP and validate the previous proposed score cutoff of $ 1,7 for species level identification in a greater collection of heterogeneous group of GPR

Summary

Introduction

Corynebacterium spp. and other Gram-positive rods (GPR) are widespread throughout nature, being most of the species part of the normal skin flora of humans and animals [1]. They are increasingly recognized as causes of human infection since immunosuppressive treatments, oncological diseases, antibiotic treatments, and multiple invasive procedures make patients vulnerable to opportunistic infections [2]. In routine laboratories the most used techniques to identify microorganisms are the conventional phenotypic tests [1,3] These tests are time consuming and do not always give reliable identification at the species level. In order to arrive to a correct molecular identification, since the 16S rRNA gene of colony on plate extraction method as previously described [10]

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Conclusion