Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Aerobic Bacteria in a Clinical Microbiology Laboratory

Myungsook Kim; Mi Jung Kwon; Hae-Sun Chung; Yangsoon Lee; Dongeun Yong; Seok Hoon Jeong; Kyungwon Lee; Yunsop Chong

doi:10.5145/KJCM.2012.15.2.60

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Kim, Kwon, Chung, Lee, Yong, Jeong, Lee, and Chong: Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Aerobic Bacteria in a Clinical Microbiology Laboratory

Original Article

Korean Journal of Clinical Microbiology

Korean Journal of Clinical Microbiology 2012; 15(2): 60-66.

Published online: 20 June 2012

DOI: https://doi.org/10.5145/KJCM.2012.15.2.60

Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Aerobic Bacteria in a Clinical Microbiology Laboratory

Myungsook Kim, Mi Jung Kwon, Hae-Sun Chung, Yangsoon Lee, Dongeun Yong, Seok Hoon Jeong, Kyungwon Lee, Yunsop Chong

Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea.

Correspondence: Dongeun Yong, Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Korea. (Tel) 82-2-2228-2442, (Fax) 82-2-313-0956, deyong@yuhs.ac

Received 13 December 2011 Revised 19 January 2012 Accepted 28 February 2012

Abstract

Background

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been used for the identification of bacteria worldwide. To our knowledge, the evaluation of MALDI-TOF MS for the identification of bacteria in Korea has not been studied. In this paper we compared the identification results of aerobic bacteria using MALDI-TOF MS to those results using conventional biochemical methods.

Methods

We evaluated the performance of a MALDI-TOF MS system (Bruker Daltonics, Leipzig, Germany) on consecutive aerobic isolates collected from January to February of 2011 which were identified using conventional methods (biochemical testing and commercial identification kits). Either directly smearing onto the target plate or protein extraction methods were additionally used if no reliable or discordant results were obtained.

Results

Among 523 isolates tested, 506 (97%) isolates had valid scores (≥2.0), 11 (2%) isolates gave intermediate scores (1.7≤ score <2.0), and 6 (1%) isolates yielded no reliable identification (score <1.7). Of the 506 valid results (score ≥2.0) by MALDI-TOF MS, the identification matched at the species level in 486 (96%) isloates, matched at the genus level in 17 (3%) isloates, and was discordant at the genus and species levels in 3 (1%) isloates.

Conclusion

The overall matching rate at the species level of MALDI-TOF MS was very high. When MALDI-TOF MS did not yield reliable results by direct smear, additional direct smears or protein extraction methods could be used to obtain better results. Our results showed that MALDI-TOF MS is a very useful method for the identification of aerobic bacteria isolated in clinical microbiology laboratories.

Keywords: Aerobic bacteria, Matrix-assisted laser desorption ionization-time of flight mass spectrometry, Species identification

Figures and Tables

Fig. 1

Comparison of identification results using MALDI-TOF MS with those using conventional methods (A) in 115 aerobic gram-positive cocci and (B) in 408 aerobic gram-negative bacilli.

Table 1

Comparison of conventional and MALDI-TOF MS identification for aerobic bacteria

Abbreviations: MS, matching at the species level; MG, matching at the genus level; NM, non-matching; NR, not reliable identification with score <1.7; GNFB, glucose nonfermenting bacilli.

Table 2

Results of MALDI-TOF MS identification after direct smear and protein extraction methods

Abbreviations: MS, matching at the species level; MG, matching at the genus level; NM, non-matching; NR, not reliable identification.

Table 3

Results analysis of the additional test using direct and protein extraction methods in the samples showing matching at genus level or non-matching on the initial analysis

Abbreviations: M, MALDI-TOF MS database related; V, Vitek2 database related; T, taxonomical. A discordant isolate might belong to multiple categories.

Table 4

Analysis of the no reliable identification results of MALDI-TOF MS

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