MALDI-TOF Mass Spectrometry: Transformative Proteomics for Clinical Microbiology

Clinical microbiology laboratories today operate with the use of a blend of high- and low-technology procedures. Despite huge steps forward in diagnostic methods based on nucleic acid amplification, clinical microbiology laboratories still rely heavily on culturing bacteria and fungi for diagnostic purposes because of the plethora and diversity of potentially isolated organisms. This process is typically done on solid (e.g., blood agar) and occasionally in liquid (i.e., broth) media. Once plate growth is observed (the so-called “colony”), the challenge is accurate identification of that growth. Historically, this identification has been considered to be a complex task, and numerous textbooks have been written about it. Traditional (phenotypic) identification of bacteria and fungi involves examination of morphologic characteristics, staining, and conducting biochemical tests (either manually or as an automated panel). Manual biochemical assays (e.g., catalase, oxidase) may provide a rapid turnaround time, but they identify only a limited number of organism types. Automated systems (e.g., VITEK®, bioMerieux; BD Phoenix™ Automated Microbiology System; MicroScan®, Siemens Healthcare Diagnostics) identify a broader range of organisms, but suffer from longer turnaround time and expensive consumables. Furthermore, the user often must have a priori knowledge of the organism type (e.g., gram-negative bacillus) being tested. Introduction of MALDI-TOF mass spectrometry into the clinical microbiology laboratory has markedly altered workflow, allowing bacterial and fungal colonies to be accurately, rapidly, and inexpensively identified. Contemporary applications in clinical microbiology combine the powerful capabilities of mass spectrometry and bioinformatics to yield a novel methodology for bacterial and fungal identification.Utilization of MALDI-TOF mass spectrometry in the clinical microbiology laboratory is explained in its simplest form by discussing the routine workflow of a microbiology technologist. Starting from a single isolated colony on a culture plate, a colony is “picked” to a spot on a MALDI-TOF mass spectrometry plate, which is a solid, typically …