Microbial survival

Microbial survival was tested in Piles 4, 5 and 6. Campylobacter was not recovered after 2 hours in any pile. E. coli was not recovered from Pile 4 after 28 hours. In Pile 5, no E. coli were recovered at 4 or 6 hours but were recovered at 9 logs at 8 hours post-inoculation (p.i.) with concurrent temperatures at near 70 C. Possible explanations for this late, positive sample are that this sample was contaminated during transport to the laboratory, in the laboratory, or came from a protected pocket within the pile. In Pile 6, no E. coli were recovered after 32 hours p.i. Salmonella was recovered until 24 hours p.i. in Pile 4; until 28 hours p.i. in Pile 5; and until 24 hours p.i. in Pile 6. Given the sensitivity of our testing was 500 cfu/ml for spiral plating and 2 cfu/ml for direct plating, these data roughly correspond to a 4 to 6 log reduction in Salmonella within 28 hours; a 5 log reduction in E. coli within 32 h, and a 2 to 3 log reduction in Campylobacter at 2 h p.i. Of the 3 bacteria tested, Salmonella was the most heat tolerant, surviving in bench tests to 122 F (50 C).