Abstract
Timeliness and accuracy in the diagnosis of microbial infections are associated with decreased mortality and reduced length of hospitalization, especially for severe, life-threatening infections. A rapid diagnosis also allows for early streamlining of empirical antimicrobial therapies, thus contributing to limit the emergence and spread of antimicrobial resistance. The introduction of matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) for routine identification of microbial pathogens has profoundly influenced microbiological diagnostics, and is progressively replacing biochemical identification methods. Compared to currently used identification methods, MALDI-TOF MS has the advantage of identifying bacteria and yeasts directly from colonies grown on culture plates for primary isolation in a few minutes and with considerable material and labor savings. The reliability and accuracy of MALDI-TOF MS in identification of clinically relevant bacteria and yeasts has been demonstrated by several studies showing that the performance of MALDI-TOF MS is comparable or superior to phenotypic methods currently in use in clinical microbiology laboratories, and can be further improved by database updates and analysis software upgrades. Besides microbial identification from isolated colonies, new perspectives are being explored for MALDI-TOF MS, such as identification of pathogens directly from positive blood cultures, sub-species typing, and detection of drug resistance determinants. In this review, we summarize the state of the art in routine identification of microbial pathogens by MALDI-TOF MS, and highlight recent advancements of this technology in special applications, such as strain typing, assessment of drug susceptibility, and detection of virulence factors.
Highlights
The application of mass spectrometry (MS) to bacterial identification was firstly proposed by Anhalt and Fenselau (1975), based on the observation that different mass spectra were obtained from bacterial extracts of different species
Microbial identification is achieved by comparing the observed spectrum with those stored in a database
The results of several studies suggest that lower score cut-off values might be applied for identification of many bacterial species without compromising accuracy (Richter et al, 2012; Szabados et al, 2012; Barnini et al, 2015), and it has been suggested that species-specific score cut-off values might be defined and applied in a species-specific manner (Richter et al, 2012) in order to optimize MALDI-TOF MS identification
Summary
The application of mass spectrometry (MS) to bacterial identification was firstly proposed by Anhalt and Fenselau (1975), based on the observation that different mass spectra were obtained from bacterial extracts of different species. Holland et al (1996) showed that specific spectral fingerprints could be obtained from whole bacterial cells by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS analysis, paving the way for microbial identification by MS. Matrix-assisted laser desorption/ionization is a soft ionization technique allowing ionization and vaporization of intact, high molecular mass biomolecules. Using a MALDI Biotyper-based identification (Bruker Daltonics), a score value between 0 and 3 is calculated by the software on the basis of peak similarities between the observed spectrum and stored reference spectra; score values of ≥2.00 indicate high confidence species ID, score values ≥1.70 and
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