Two
serine protease enzymes,
subtilisin 309 and
subtilisin 309-v, were used to digest brain homogenates containing high levels of
prion infectivity using mildly alkaline conditions to investigate
prion decontamination methods. To establish that
PrP(res) infectivity was eliminated, we utilized the Rocky Mountain Laboratory (RML) mouse-adapted
scrapie model system for bioassay. Only one digestion condition (
subtilisin 309 at 138mAU/ml, 55 degrees C and 14h digestion time pH 7.9) was considered to be highly relevant statistically (P<0.001) compared to control, with 52% of challenged mice surviving until the end of the study period. In contrast, treatment of
PrP(res) by autoclaving at 134 degrees C or treatment with
hypochlorite at a concentration of 20,000 ppm completely protected mice from prionosis. Further, in vitro assays suggest that potential proteolytic based
PrP(res) decontamination methods must use high
enzyme concentration, pH values >9.0, and elevated temperatures to be a safely efficacious, thereby limiting applicability on delicate
surgical instruments and use in the environment.