Biochemical evidence for the proteolytic degradation of infectious prion protein PrP^sc in hamster brain homogenates by foodborne bacteria

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°C, 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.