Abstract
MALDI-TOF mass spectrometry has revolutionized clinical microbiology diagnostics by delivering accurate, fast, and reliable identification of microorganisms. It is conventionally based on the detection of intracellular molecules, mainly ribosomal proteins, for identification at the species-level and/or genus-level. Nevertheless, for some microorganisms (e.g., for mycobacteria) extensive protocols are necessary in order to extract intracellular proteins, and in some cases a protein-based approach cannot provide sufficient evidence to accurately identify the microorganisms within the same genus (e.g., Shigella sp. vs E. coli and the species of the M. tuberculosis complex). Consequently lipids, along with proteins are also molecules of interest. Lipids are ubiquitous, but their structural diversity delivers complementary information to the conventional protein-based clinical microbiology matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) based approaches currently used. Lipid modifications, such as the ones found on lipid A related to polymyxin resistance in Gram-negative pathogens (e.g., phosphoethanolamine and aminoarabinose), not only play a role in the detection of microorganisms by routine MALDI-TOF mass spectrometry but can also be used as a read-out of drug susceptibility. In this review, we will demonstrate that in combination with proteins, lipids are a game-changer in both the rapid detection of pathogens and the determination of their drug susceptibility using routine MALDI-TOF mass spectrometry systems.
Highlights
In recent years, matrix-assisted laser desorption ionization/timeof-flight (MALDI-TOF) mass spectrometry (MS) has revolutionized the field of microbiology (Clark et al, 2013; Singhal et al, 2015)
Lipids have been used to characterize microorganisms since the 1960s (Abel et al, 1963; Moss and Lewis, 1967; Moss et al, 1980), the initial gas chromatography methods used for lipid analysis were time-consuming and unsuitable for clinical use
Analysis of lipids by MALDI-TOF MS is a promising tool for the detection of antibiotic resistance, in the case of rapidly spreading resistance to polymyxins
Summary
Matrix-assisted laser desorption ionization/timeof-flight (MALDI-TOF) mass spectrometry (MS) has revolutionized the field of microbiology (Clark et al, 2013; Singhal et al, 2015). Laborintensive protocols involving protein precipitation with ethanol and subsequent extraction with formic acid and acetonitrile are used for yeasts to improve identification results (Bader, 2017) Another major constraint of MALDI-TOF MS is a commonly encountered failure to differentiate some closely related species (Bizzini et al, 2010; Alcaide et al, 2018). In contrast to glycerol-ester phospholipids from bacteria and filamentous fungi archaebacterial membranes are composed of isoprenoid and hydroisoprenoid hydrocarbons and isopranyl glycerol-ether lipids (De Rosa et al, 1986) These structures vary according to phenotypes (e.g., halophiles, methanogens, and thermophiles), these molecules are formed by condensation of glycerol or more complex polyols with isoprenoid alcohols containing 20, 25, or 40 carbon atoms (Woese et al, 1978; De Rosa et al, 1986).
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