MALDI‐TOF MS for Identification of Acid‐Fast Bacilli and Aerobic Actinomycetes

Abstract This chapter describes the use of matrix‐assisted laser desorption ionization–time of flight mass spectrometry (MALDI‐TOF MS) for the identification of mycobacteria, Nocardia, and other aerobic actinomycetes after growth in culture. It evaluates the MALDI‐TOF MS technique results in a spectral profile that relates to the mass‐to‐charge ratio of the organism. Direct spotting or on‐target extraction is not advised for myco‐bacteria due to safety concerns and the cell wall properties of this microorganism group. For these reasons, tube extraction protocols are recommended and typically involve mechanical disruption via bead beating, sonication, and/ or vortexing in ethanol, formic acid, and/or acetonitrile. The extracted proteins are then spotted onto the target plate for MALDI‐TOF MS analysis, where the microbial profile is then compared with a reference database; matching algorithms are used to determine the organism's identity.