Ann Lab Med.  2016 Jul;36(4):325-334. 10.3343/alm.2016.36.4.325.

Identification of Acinetobacter Species Using Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

• Jeong S
• Hong JS
• Kim JO
• Kim KH
• Lee W
• Bae IK
• Lee K
• Jeong SH

• KMID: 2373552
• DOI: http://doi.org/10.3343/alm.2016.36.4.325

Abstract

BACKGROUND
Acinetobacter baumannii has a greater clinical impact and exhibits higher antimicrobial resistance rates than the non-baumannii Acinetobacter species. Therefore, the correct identification of Acinetobacter species is clinically important. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has recently become the method of choice for identifying bacterial species. The purpose of this study was to evaluate the ability of MALDI-TOF MS (Bruker Daltonics GmbH, Germany) in combination with an improved database to identify various Acinetobacter species.
METHODS
A total of 729 Acinetobacter clinical isolates were investigated, including 447 A. baumannii, 146 A. nosocomialis, 78 A. pittii, 18 A. ursingii, 9 A. bereziniae, 9 A. soli, 4 A. johnsonii, 4 A. radioresistens, 3 A. gyllenbergii, 3 A. haemolyticus, 2 A. lwoffii, 2 A. junii, 2 A. venetianus, and 2 A. genomospecies 14TU. After 212 isolates were tested with the default Bruker database, the profiles of 63 additional Acinetobacter strains were added to the default database, and 517 isolates from 32 hospitals were assayed for validation. All strains in this study were confirmed by rpoB sequencing.
RESULTS
The addition of the 63 Acinetobacter strains' profiles to the default Bruker database increased the overall concordance rate between MALDI-TOF MS and rpoB sequencing from 69.8% (148/212) to 100.0% (517/517). Moreover, after library modification, all previously mismatched 64 Acinetobacter strains were correctly identified.
CONCLUSIONS
MALDI-TOF MS enables the prompt and accurate identification of clinically significant Acinetobacter species when used with the improved database.

Keyword

MALDI-TOF MS; Acinetobacter; Species; Identification; Database

MeSH Terms

Acinetobacter Infections/*microbiology/pathology
Acinetobacter baumannii/*chemistry/classification/isolation & purification
Bacterial Proteins/chemistry/genetics/metabolism
Databases, Factual
Humans
Phylogeny
RNA, Ribosomal, 16S/chemistry/genetics/metabolism
*Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Bacterial Proteins
RNA, Ribosomal, 16S

Figure

• 

  Fig. 1 Dendrogram of the protein signatures of the updated 63 Acinetobacter strains, derived from matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) data. A. bereziniae, A. soli, A. gyllenbergii, A. junii, A. venetianus, and A. genomospecies 14TU that were not in the default Bruker database are presented. All distance values are relative and normalized to a maximal value of 1,000.

• 

  Fig. 2 Peak profiles of 15 representative Acinetobacter species generated by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The mass-to-charge (m/z) ratios of the ions are shown on the x-axis, and the absolute intensities of the ions are presented on the y-axis. AU values were given by the software.Abbreviation: AU, arbitrary intensity.

• 

  Fig. 3 Dendrogram constructed from the specific matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS)-generated mass spectra of A. baumannii, A. nosocomialis, and A. pittii within the improved database (which includes the original Bruker database). The protein profiles from A. baumannii isolates formed a separate cluster. The A. baumannii protein profiles were more closely associated with those from A. nosocomialis than those from A. pittii. All relative distance values are normalized to a maximal value of 1,000.

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