: Abnormal prion protein (PrPSc) is highly resistant to inactivation by conventional chemical and physical means.
This study was to determine if microbes from the environment could be used to degrade PrPSc in central nervous system
(CNS) tissues from scrapie positive sheep as measured by Western blot. In the first experiment, the number of microbes in
CNS tissue suspended in saline was reduced by autoclaving the suspension at 121°C for 5 minutes. Aliquots of this
preparation were then inoculated with additional ovine fecal microbes and controls were not inoculated. The results
showed that the addition of microbes increased the degradation of PrPSc in specimens during incubation at room
temperature (RT) or at 60°C, but the reduction was greatest at 60°C. In the second experiment, a separate tissue
suspension in saline was prepared from CNS tissue from each of 4 scrapie positive sheep and from each of 4 negative
sheep. All specimens contained bacteria and after 90 days of incubation at 60°C, PrPSc in CNS specimens was degraded
beyond the detection limit in tissues from 2 scrapie positive sheep and was partially degraded in the other two specimens.
The tissues from scrapie negative sheep were consistently negative for PrPSc. Analysis of microbial 16S ribosomal DNA
indicated that during the 90 day incubation period the microbe population shifted from a predominance of mesophiles to
thermophiles, based on guanine-cytosine (GC) content of ribosomal RNA genes. The results in this study suggest that
microbes commonly found in sheep carcasses or manure could play a role in the degradation of PrPSc in CNS tissues
during incubation at 60°C.