3 Otto Holst (ed.), Microbial Toxins: Methods and Protocols, Methods in Molecular Biology, vol. 739, DOI 10.1007/978-1-61779-102-4_1, © Springer Science+Business Media, LLC 2011 Chapter 1 Detection of Bacterial Protein Toxins by Solid Phase Magnetic Immunocapture and Mass Spectrometry Gabriella Pocsfalvi and Gitta Schlosser Abstract Bacterial protein toxins are involved in a number of infectious and foodborne diseases and are considered as potential biological warfare agents as well. Their sensitive multiplex detection in complex environmen- tal, food, and biological samples are an important although challenging task. Solid-phase immunoaffinity capture provides an efficient way to enrich and purify a wide range of proteins from complex mixtures. We have shown that staphylococcal enterotoxins, for example, can be efficiently enriched by means of magnetic immunocapture using antibody functionalized paramagnetic beads. The method was success- fully interfaced by the on-beads and off-beads detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry at the protein level and by the off-beads nano-electrospray ionization- MS/MS detection at the enzyme digests level, enabling thus the unambiguous identification of the toxin. The method is applicable to any bacterial toxin to which an antibody is available. Key words: Bacterial protein toxins, Staphylococcal enterotoxins, Immunomagnetic separation, Immunoaffinity, Magnetic beads, Mass spectrometry, MALDI, ESI Mass spectrometry (MS) has been successfully applied in the detection, identification, quantification, and structural character- ization of biological toxins (1, 2), including bacterial protein tox- ins, such as botulinum (3–7), shiga-like (8), tetanus (9), anthrax (10) toxins, and staphylococcal enterotoxins (SEs) (2, 11). Both matrix-assisted laser desorption/ionization (MALDI) (12) and electrospray ionization (ESI) (9) techniques have been widely exploited for the characterization of protein toxins. Their direct detection in complex biological samples like body fluids and food 1. Introduction