Western blot assessment of prion inactivation by alkali treatment in the process of horticultural fertilizer production from meat meal

Western blot detection of the abnormal isoform of the prion protein (PrPSc) was used to assess prion inactivation by heating under alkaline conditions during the manufacturing process used to produce horticultural fertilizer from meat meal. PrPSc was detected in the sample prepared from the horticultural fertilizer spiked with a 0.25 µg equivalent of scrapie-infected mouse brain. In contrast, PrPSc was not detected in a sample containing 0.25 g brain equivalent prepared from a small-scale processed mixture of scrapie-infected mouse brain and meat meal using the same method as that used to produce horticultural fertilizer. Our results indicated that the amount of PrPSc decreased to at least 1/106 by processing with heating under alkaline conditions. Although the bioassay suggests that prion infectivity was reduced under these conditions, this procedure did not completely remove high-titer prion infectivity.