Validation of a novel automatic deposition of bacteria and yeasts on MALDI target for MALDI-TOF MS-based identification using MALDI Colonyst robot

PLoS One. 2017 Dec 29;12(12):e0190038. doi: 10.1371/journal.pone.0190038. eCollection 2017.

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) -based identification of bacteria and fungi significantly changed the diagnostic process in clinical microbiology. We describe here a novel technique for bacterial and yeast deposition on MALDI target using an automated workflow resulting in an increase of the microbes' score of MALDI identification. We also provide a comparison of four different sample preparation methods. In the first step of the study, 100 Gram-negative bacteria, 100 Gram-positive bacteria, 20 anaerobic bacteria and 20 yeasts were spotted on the MALDI target using manual deposition, semi-extraction, wet deposition onto 70% formic acid and by automatic deposition using MALDI Colonyst. The lowest scores were obtained by manual toothpick spotting which significantly differ from other methods. Identification score of semi-extraction, wet deposition and automatic wet deposition did not significantly differ using calculated relative standard deviation (RSD). Nevertheless, the best results with low error rate have been observed using MALDI Colonyst robot. The second step of validation included processing of 542 clinical isolates in routine microbiological laboratory by a toothpick direct spotting, on-plate formic acid extraction (for yeasts) and automatic deposition using MALDI Colonyst. Validation in routine laboratory process showed significantly higher identification scores obtained using automated process compared with standard manual deposition in all tested microbial groups (Gram-positive, Gram-negative, anaerobes, and yeasts). As shown by our data, automatic colony deposition on MALDI target results in an increase of MALDI-TOF MS identification scores and reproducibility.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Automation
  • Bacteria / isolation & purification*
  • Robotics*
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*
  • Yeasts / isolation & purification*

Grants and funding

This work was partially supported by the Charles University Research Fund Progres (project number Q39), by the National Sustainability Program I (NPU I) Nr. LO1503 provided by the Ministry of Education Youth and Sports of the Czech Republic. Partial support by the company BioVendor – Laboratorní medicína, a.s. (Brno, Czech Republic) as a contractual research performed in Biomedical Center of Faculty of Medicine in Plzen. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.