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Evaluation of four pretreatment procedures for MALDI-TOF MS yeast identification in the routine clinical laboratory

Carole Cassagne1, Anne-Laure Cella, Pierre Suchon

  • 1Laboratoire de Parasitologie-Mycologie, CHU Timone, Université de la Méditerranée, F-13385 Marseille, France. carole.cassagne@ap-hm.fr

Medical Mycology
|September 18, 2012
PubMed

Insights

Complete formic acid/acetonitrile extraction methods significantly improve Matrix-Assisted Laser Desorption/Ionization-Time Of Flight Mass Spectrometry (MALDI-TOF MS) yeast identification accuracy in clinical labs. Simpler methods like direct smear or fast formic acid extraction yield unreliable results.

Area of Science:

  • Clinical Microbiology
  • Analytical Chemistry
  • Biotechnology

Background:

  • Matrix-Assisted Laser Desorption/Ionization-Time Of Flight Mass Spectrometry (MALDI-TOF MS) is crucial for yeast identification.
  • Standardized pretreatment protocols are essential for reliable MALDI-TOF MS results.
  • Existing literature describes four main pretreatment methods: direct smear, fast formic acid, and two complete formic acid/acetonitrile extractions.

Purpose of the Study:

  • To compare the impact of four different yeast pretreatment methods on MALDI-TOF MS identification performance.
  • To evaluate the accuracy and reliability of yeast identification using colonies grown on Sabouraud or chromogenic media.
  • To determine the optimal pretreatment procedure for clinical laboratory settings.

Main Methods:

  • Compared four pretreatment procedures (direct smear, fast formic acid, two complete formic acid/acetonitrile extractions) for MALDI-TOF MS yeast identification.
  • Utilized 103 yeast isolates from clinical samples.
  • Assessed correct identification rates (with and without LogScore cutoff) and reliable identification rates (LogScore ≥ 2).

Main Results:

  • All methods achieved >85% correct yeast identification, irrespective of LogScore.
  • Complete formic acid/acetonitrile extractions yielded significantly superior results compared to smear and fast formic acid methods on Sabouraud media.
  • Reliable identification rates were <40% for smear and fast formic acid, versus >77% for complete extraction methods on both media types.

Conclusions:

  • Direct smear and fast formic acid pretreatment methods are not recommended for clinical MALDI-TOF MS yeast identification due to consistently low LogScore values.
  • Complete formic acid/acetonitrile extraction procedures offer superior accuracy and reliability for MALDI-TOF MS-based yeast identification.
  • Despite being more labor-intensive, complete extraction methods are better suited for clinical laboratory applications.

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