Current status of MALDI-TOF mass spectrometry in clinical microbiology

Abstract

Mass spectrometry (MS) is a type of analysis used to determine what molecules make up a sample, based on the mass spectrum that are created by the ions. Mass spectrometers are able to perform traditional target analyte identification and quantitation; however, they may also be used within a clinical setting for the rapid identification of bacteria. The causative agent in sepsis is changed over time, and clinical decisions affecting the management of infections are often based on the outcomes of bacterial identification. Therefore, it is essential that such identifications are performed quickly and interpreted correctly. Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometer is one of the most popular MS instruments used in biology, due to its rapid and precise identification of genus and species of an extensive range of Gram-negative and -positive bacteria. Microorganism identification by Mass spectrometry is based on identifying a characteristic spectrum of each species and then matched with a large database within the instrument. The present review gives a contemporary perspective on the challenges and opportunities for bacterial identification as well as a written report of how technological innovation has advanced MS. Future clinical applications will also be addressed, particularly the use of MALDI-TOF MS in the field of microbiology for the identification and the analysis of antibiotic resistance.

Keywords: Antibiotic susceptibility testing; MALDI-TOF MS; Mass spectrometry; Microbiology; Microorganism identification.

Fig. 1

MALDI-TOF MS methodology. The sample is co-crystallized with the matrix on the sample target and to be desorbed and ionized by the MALDI ion source (e.g. ultraviolet laser). The ion molecules, including the microbial peptides/proteins, are accelerated by the electric field into the TOF analyzer. All the ions are separated by TOF in accordance with the m/z ratio and a mass spectrum.

Fig. 2

MALDI-TOF MS microorganism identification workflow in a clinical laboratory. All the bacterial colonies from a standard culture in a solid agar plate are applied directly via the standard smear method. Some liquid samples of urgent specimens, such as blood culture positive bottles and body fluids (CSF or urine), can be applied for direct identification after a multi-step sample preparation and extraction protocol. Mycobacterium spp. are applied following a specific sample preparation protocol for their rapid identification.