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

PrP super(Sc) is a general term to describe the infectious agent causing transmissible spongiform encephalopathy (TSE), and the protease-resistant form of cellular PrP super(C). In this study, we have identified several protease- secreting bacteria able to degrade PrP super(Sc) under more or less native conditions (30 degree 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 super(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 super(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 super(Sc). Our study also suggests the potential use of such starter bacteria or their proteases for application in PrP super(Sc) degradation and decontamination under native conditions.