임상미생물 검사실에서 산소성 세균 동정을 위한 Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry의 유용성
Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Aerobic Bacteria in a Clinical Microbiology Laboratory
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배경: MALDI-TOF MS 기법을 이용한 세균 동정은 외국에서는 많은 평가 보고가 있어왔으나 국내에서는 아직 평가된 바 없었다. 이에 저자들은 국내 대학병원 임상미생물 검사실에서 전통적인 생화학적 방법 혹은 동정용 키트를 이용한 산소성 세균의 균종 동정결과와 MALDI-TOF MS 동정 결과를 비교 평가하고자 하였다. 방법: 2011년 1월부터 2월까지 세브란스병원 진단검사의학과 미생물 검사실에 균배양을 의뢰한 일련 검체에서 분리된 산소성 세균 523주의 전통적 동정법과 MALDI-TOF MS 동정 결과를 비교하였다. MALDI-TOF MS의 직접 도말법으로 동정치가 1.7 미만으로 동정 결과를 신뢰할 수 없었던 균주와 전통적 방법과 균속까지 일치하였거나 균종명과 균속명이 모두 불일치하였던 일부 균주는 직접 도말법 재검과 단백추출법을 추가로 시행하였다. 결과: 산소성 세균 523주 중 506주(97%)는 동정치 2.0 이상, 11주(2%)는 1.7 이상에서 2.0 미만이었다. 동정치가 2.0 이상인 506주 중 전통정 동정법 결과와 비교하였을 때 균종 일치는 486주(96%), 균속 일치는 17주(3%), 불일치는 3주(1%)이었다. 결론: MALDI-TOF MS를 이용한 산소성 세균의 동정은 생화학적 성상을 기반으로 하는 상품화 키트를 포함한 전통적 동정 방법과 높은 일치율을 보였다. 동정치가 1.7 미만으로 결과를 신뢰할 수 없는 경우에도 직접도말법과 단백추출법을 추가하면 대부분 균종 동정 결과를 얻을 수 있었다. 따라서 MALDI-TOF MS 동정은 임상미생물 검사실에서 통상적으로 분리되는 산소성 세균의 동정 방법으로 매우 유용할 것으로 판단되었다.
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 MALDITOF 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.
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