Systematic and Applied Microbiology 29 (2006) 165–171 Biochemical evidence for the proteolytic degradation of infectious prion protein PrP sc in hamster brain homogenates by foodborne bacteria Simone Mu¨ller-Hellwig a , Martin H. Groschup b , Rohtraud Pichner c , Manfred Gareis c , Erwin Ma¨rtlbauer d , Siegfried Scherer a , Martin J. Loessner e,Ã a Abteilung Mikrobiologie, Zentralinstitut fu¨r Erna¨hrungs- und Lebensmittelforschung, Technische Universita¨t Mu¨nchen, D-85350 Freising-Weihenstephan, Germany b Friedrich-Loeffler-Institut, Institute for Novel and Emerging Diseases, D-17498 Insel Riems, Germany c Bundesforschungsanstalt fu¨r Erna¨hrung und Lebensmittel, Institut fu¨r Mikrobiologie und Toxikologie, D-95326 Kulmbach, Germany d Ludwig-Maximilian Universita¨t Mu¨nchen, Lehrstuhl fu¨r Hygiene und Technologie der Milch, D-85754 Oberschleissheim, Germany e Institute for Food Science and Nutrition, Swiss Federal Institute of Technology (ETH), Schmelzbergstrasse 7, CH-8092 Zu¨rich, Switzerland Received 13 July 2005 Abstract PrP Sc is a general term to describe the infectious agent causing transmissible spongiform encephalopathy (TSE), and the protease-resistant form of cellular PrP C . In this study, we have identified several protease-secreting bacteria able to degrade PrP Sc under more or less native conditions (30 1C, pH 8), focusing on strains isolated mainly from cheese. One hundred and ninty-nine protease-secreting isolates belonging to the Actinomycetales and Bacillales were screened for the expression of PrP Sc degrading activity by a Western blot procedure. Only 6 strains belonging to the following species were found to exhibit such an activity: Arthrobacter nicotianae, Bacillus licheniformis, Brachybacterium conglomeratum, Brachybacterium tyrofermentans and Staphylococcus sciuri and Serratia spp. As revealed by a general protease assay based on dye-labeled Azocoll substrate, the PrP Sc degrading activity was not directly correlated to the total level of secreted proteolytic activity of these organisms. This indicates that specific proteases are required for the degradation of PrP Sc . Our study also suggests the potential use of such starter bacteria or their proteases for application in PrP Sc degradation and decontamination under native conditions. r 2005 Elsevier GmbH. All rights reserved. Keywords: Prion protein; Scrapie; BSE; PrP Sc ; Bacterial protease; Degradation; Food Introduction Transmissible spongiform encephalopathies (TSE) are fatal neurodedegenerative disorders of humans and animals [2,28]. This group of diseases includes, among others, Creutzfeldt–Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) and Scrapie in different animals [1]. It is now known that these diseases are caused by an abnormal conformational variant of a physiological protein, termed prion protein (PrP c ). Prions are defined as ‘‘small proteinaceous infectious particles which resist inactivation by ARTICLE IN PRESS www.elsevier.de/syapm 0723-2020/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.syapm.2005.07.010 Ã Corresponding author. Tel.: +41 44 632 3335; fax: +41 44 632 1266. E-mail address: martin.loessner@ilw.agrl.ethz.ch (M.J. Loessner).