Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/20/2013
Publication Date: 11/3/2013
Publication URL: http://handle.nal.usda.gov/10113/59684
Citation: Gurtler, J., Boateng, A.A., Han, Y.H., Douds, D.D. 2014. Inactivation of E.coli 0157:H7 in cultivable soil by fast and slow pyrolysis-generated biochars. Foodborne Pathogens and Disease. 11:215-223. Interpretive Summary: Biochar is a fine, grainy byproduct of burning organic matter in no- or low-oxygen generators. Benefits of biochar production include generation of bio-fuels (through fast-pyrolysis (FP)), useful soil amendments for fertilizing crops and binding heavy metals, binding up environmental biocarbon, and reducing environmental gas emissions. We tested twelve types of biochar for the ability to inactivate E. coli O157:H7 (EHEC) in crop soil. Soil+biochar samples were adjusted to a final moisture content of 17.6 percent and stored at 22 degrees Celsius. FP biochar that was generated from switchgrass and horse litter were the most effective, inactivating over 99% of E. coli in soil within 2 weeks. Two other FP biochars (generated from oak as well as switchgrass pellets) performed favorably. Four of eight slow-pyrolysis biochars (from hardwood pellets and switchgrass, generated under various times and temperatures) inactivated some E. coli, although at lower levels than the FP biochars did. These results are the first to suggest that biochar amendments enhance the inactivation of E. coli O157:H7 in cultivable soil and may be useful in improving the safety of fruits and vegetables.
Technical Abstract: Biochar is a byproduct of incomplete combustion of organic matter, producing a fine, grainy, highly porous material. Benefits of biochar production include generation of bio-fuels, useful soil amendments for fertilizing crops, binding heavy metals, sequestering environmental biocarbon, and reducing environmental gas emissions. The objective of this study was to determine the influence of fast-pyrolysis (FP) and slow-pyrolysis (SP) biochars on the survival of enterohemorrhagic E. coli O157:H7 (EHEC) in cultivable soil, as recovered on selective modified Eosin Methylene Blue (EMB) agar and a non-selective medium. A two-strain composite of EHEC was added to autoclaved cultivable soil (7 log CFU/g, final population) + one of 12 types of biochar (10 percent final concentration in soil). Soil+biochar samples were adjusted to a final moisture content of 17.6 percent (wt:wt) and stored in sealed bags at 22 degrees C. Populations of EHEC were determined weekly for up to eight weeks. FP-switchgrass (FP-SG) and FP-horse litter (FP-HL) biochars inactivated 2.8 and 2.1 log CFU/g more EHEC than did control soil by day 14. Inactivation of EHEC, to undetectable levels by direct plating, were accomplished by week 4 with the FP-switchgrass treatment and by week 5 by FP-switchgrass pellets and FP-oak treatments. Positive-control soil sample mean populations of EHEC, by comparison, remained as high as 5.8 and 4.0 log CFU/g at weeks 4 and 5, respectively. Additionally, four more SP treatments (viz., hardwood pellets and switchgrass, both generated at 700 degrees C - 30 min, as well as hardwood pellets 500 degrees C – 1 h) inactivated greater numbers of cells than control soil alone at week 4, 5, and 6 sampling times. Modified EMB agar recovered significantly fewer cells than non-selective TSA and was used to determine injury of cells, which ranged from 0.3 – 1.3 log CFU/g. These results are the first to suggest that biochar amendments enhance the inactivation of E. coli O157:H7 in cultivable soil.