ARS | Publication request: Soil solarization reduces Escherichia coli O157:H7 and total Escherichia coli on cattle feedlot pen surfaces

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 27, 2011
Publication Date: January 4, 2012
Citation: Berry, E.D., Wells, J. 2012. Soil solarization reduces Escherichia coli O157:H7 and total Escherichia coli on cattle feedlot pen surfaces. Journal of Food Protection. 75(1):7-13.

Interpretive Summary: Cattle that are infected with the human pathogen E. coli O157:H7 shed the organism in their feces. The resulting manure containing E. coli O157:H7 can be a source of the organism to infect other cattle in the same pen. Therefore, reducing E. coli O157:H7 in the manure may reduce the spread and occurrence of this pathogen among cattle. Soil solarization is a preplanting pathogen and pest control technique used in crop production that utilizes solar energy to heat the soil. Typically, the soil is covered with transparent polyethylene plastic sheets for a period of several weeks, and the resultant heat can inactivate plant pathogens, weeds, and weed seeds in the covered soil. The objective of this study was to investigate the ability of soil solarization to reduce E. coli O157:H7 in feedlot pen surface manure. Cattle were removed from a feedlot pen, and we compared the reduction of E. coli O157:H7 and total nonpathogenic E. coli in solarized and unsolarized plots in the pen. E. coli O157:H7 was no longer detectable in the feedlot surface manure by 8 weeks of solarization, but was still detected in unsolarized feedlot surface manure at 10 weeks. There was a 99.9% reduction of total E. coli levels after 6 weeks of solarization, but levels of total E. coli remained high for 10 weeks in feedlot surface manure that was not solarized. Because soil solarization effectively reduces E. coli O157:H7, this technique may be useful for reducing the transmission and persistence of this pathogen in cattle production, in addition to reducing E. coli O157:H7 in contaminated soils that will be used to grow food crops.

Technical Abstract: Feedlot pen soils are a source for transmission of Escherichia coli O157:H7, and therefore a target for preharvest strategies to reduce this pathogen in cattle. The objective of this study was to determine the ability of soil solarization to reduce E. coli O157:H7 in feedlot surface material (FSM). A feedlot pen was identified in which naturally occurring E. coli O157:H7 was prevalent and evenly distributed in the FSM. Forty 3- × 3-m plots were randomly assigned such that 5 plots of each of the solarization times of 0, 1, 2, 3, 4, 6, 8, and 10 weeks were examined. Temperature loggers were placed 7.5 cm below the surface in the center of each plot, and plots to be solarized were covered with clear 6 mil polyethylene. At each sampling time, 5 FSM samples were collected from each plot (5 solarized and 5 unsolarized plots; n = 25). Generic E. coli concentrations and E. coli O157:H7 presence by immunomagnetic separation and plating were determined for each FSM sample. Initial percentages of E. coli O157:H7-positive samples in control and solarized FSM were 84 and 80%, respectively, and did not differ (P > 0.05). E. coli O157:H7 was no longer detectable by 8 weeks of solarization, but was still detected in unsolarized FSM at 10 weeks. The average initial concentration of generic E. coli in FSM was 5.56 log CFU/g, and did not differ between treatments (P > 0.05). There was a rapid 2.0-log decrease of E. coli after 1 week of solarization, and a >3.0-log reduction of E. coli by week 6 of solarization (P < 0.05). Generic E. coli levels remained unchanged in unsolarized FSM (P > 0.05). Daily peak FSM temperatures were on average 8.7°C degrees higher for solarized FSM in comparison to unsolarized FSM, and reached temperatures as high as 57°C. Because soil solarization effectively reduces E. coli O157:H7, this technique may be useful for reduction of transmission and persistence of this pathogen in cattle production, in addition to remediation of E. coli O157:H7-contaminated soils used to grow food crops.