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

• Published in: Journal of Clinical Microbiology Vol. 48; no. 11; pp. 4015 - 4021
• Main Authors: Verroken, A, Janssens, M, Berhin, C, Bogaerts, P, Huang, T.-D, Wauters, G, Glupczynski, Y
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01-11-2010; American Society for Microbiology (ASM)
• Subjects: Bacterial Typing Techniques; Bacteriological Techniques - methods; Bacteriology; Biological and medical sciences; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; DNA, Ribosomal - chemistry; DNA, Ribosomal - genetics; Fundamental and applied biological sciences. Psychology; Germany; Humans; Microbiology; Miscellaneous; Mycobacteriology and Aerobic Actinomycetes; Nocardia; Nocardia - chemistry; Nocardia - classification; Nocardia - isolation & purification; Nocardia Infections - diagnosis; Nocardia Infections - microbiology; RNA, Ribosomal, 16S - genetics; Sensitivity and Specificity; Sequence Analysis, DNA; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Germany; Actinomycetales; Nocardia; Bacteria; Nocardiaceae; Actinomycetes; Identification; Matrix assisted laser desorption ionization
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.01234-10

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 ionization-time of flight mass spectrometry (MALDI-TOF MS). As reference methods for species identification, full-length 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.