Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Nocardia Species

Abstract

The identification of Nocardia species, usually based on biochemical tests together with phenotypic in vitro susceptibility and resistance patterns, is a difficult and lengthy process owing to the slow growth and limited reactivity of these bacteria. In this study, a panel of 153 clinical and reference strains of Nocardia spp., altogether representing 19 different species, were characterized by matrix-assisted laser desorption ionizationtime of flight mass spectrometry (MALDI-TOF MS). As reference methods for species identification, fulllength 16S rRNA gene sequencing and phenotypical biochemical and enzymatic tests were used. In a first step, a complementary homemade reference database was established by the analysis of 110 Nocardia isolates (pretreated with 30 min of boiling and extraction) in the MALDI BioTyper software according to the manufacturer's recommendations for microflex measurement (Bruker Daltonik GmbH, Leipzig, Germany), generating a dendrogram with species-specific cluster patterns. In a second step, the MALDI BioTyper database and the generated database were challenged with 43 blind-coded clinical isolates of Nocardia spp. Following addition of the homemade database in the BioTyper software, MALDI-TOF MS provided reliable identification to the species level for five species of which more than a single isolate was analyzed. Correct identification was achieved for 38 of the 43 isolates (88%), including 34 strains identified to the species level and 4 strains identified to the genus level according to the manufacturer's log score specifications. These data suggest that MALDI-TOF MS has potential for use as a rapid (<1 h) and reliable method for the identification of Nocardia species without any substantial costs for consumables.

Lung <i>Nocardia elegans</i> Infection Diagnosed on Matrix-assisted Laser Desorption Ionization-time of Flight Mass Spectrometry (MALDI-TOF MS)

“…Their method involves identifying a microorganism by searching a library for the ribosomal 16S protein. Furthermore, MALDI-TOF MS demonstrates high sensitivity for rapidly and easily identifying Nocardia species (13); however, the high cost of dedicated MALDI-TOF devices is comparable with that of laboratory equipment (13). Using the MALDI-TOF method, we were able to identify N. elegans as the causative pathogen in the present case.…”

“…MALDI-TOF MS is a new method for performing microbiology laboratory work that is capable of confirming the identity of several microorganisms known to be difficult to identify using conventional tests. Verroken et al established a method for rapidly and easily identifying Nocardia sp., including N. elegans, and reported the advantages of MALDI-TOF MS (13). Their method involves identifying a microorganism by searching a library for the ribosomal 16S protein.…”

Comparison of two matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry methods and API 20AN for identification of clinically relevant anaerobic bacteria

“…Bruker MS (Microflex; Bruker Daltoniks), VITEK MS (bioMérieux) and Shimadzu MS (AXIMA; Shimadzu Corporation). They are used to identify aerobic and anaerobic bacteria (Fedorko et al, 2012;Nagy et al, 2009Nagy et al, , 2012van Veen et al, 2010;Veloo et al, 2011b), mycobacteria (Saleeb et al, 2011), Nocardia (Verroken et al, 2010) and yeasts (van Veen et al, 2010) isolated on solid media from clinical specimens. MALDI-TOF MS has also been recently used for the identification of bacteria and yeasts directly from positive blood culture bottles (Ferroni et al, 2010;Stevenson et al, 2010).…”

MALDI-TOF MS: Its Application in the Clinical Laboratory and a Paradigm Shift in Clinical Microbiology

“…However, as analysis of microorganisms by MALDI-TOF MS became more commonplace, it became apparent that the IC method was not always appropriate for all specimen types, in spite of its relative simplicity; problems with spectral generation from some microbes [12,13] and biosafety issues [14,15] and interpretation forms are shown in Fig. 1.…”