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Inactivation of E. coli O157:H7 in Cultivable Soil by Fast and Slow Pyrolysis-Generated Biochar

Gurtler, Joshua B., Boateng, Akwasi A., Han, Yanxue (Helen), Douds, David D.
Foodborne pathogens & disease 2013
Escherichia coli O157, Panicum virgatum, Quercus, bacterial contamination, biochar, food contamination, fresh produce, hardwood, horse manure, pathogen survival, pyrolysis, risk, soil
An exploratory study was performed to determine the influence of fast pyrolysis (FP) and slow pyrolysis (SP) biochars on enterohemorrhagic Escherichia coli O157:H7 (EHEC) in soil. Soil + EHEC (inoculated at 7 log colony-forming units [CFU]/g of soil) + 1 of 12 types of biochar (10% total weight:weight in soil) was stored at 22°C and sampled for 8 weeks. FP switchgrass and FP horse litter biochars inactivated 2.8 and 2.1 log CFU/g more EHEC than no-biochar soils by day 14. EHEC was undetectable by surface plating at weeks 4 and 5 in standard FP switchgrass, FP oak, and FP switchgrass pellet biochars. Conversely, EHEC populations in no-biochar control samples remained as high as 5.8 and 4.0 log CFU/g at weeks 4 and 5, respectively. Additionally, three more SP hardwood pellet biochars (generated at 500°C for 1 h, or 2 h, or generated at 700°C for 30 min) inactivated greater numbers of EHEC than did the no-biochar control samples during weeks 4 and 5. These results suggest that biochar can inactivate E. coli O157:H7 in cultivable soil, which might mitigate risks associated with EHEC contamination on fresh produce.