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T7-12 Population Dynamics of Generic Escherichia coli and Surrogate Escherichia coli O157:H7 in Manure-amended Soils

Tuesday, August 5, 2014: 4:45 PM
Room 111-112 (Indiana Convention Center)
Manan Sharma, U.S. Department of Agriculture-ARS, Beltsville, MD
Lorna Graham, University of Maryland Eastern Shore, Princess Anne, MD
June deGraft-Hanson, U.S. Food and Drug Administration, College Park, MD
Daniel Wright, University of Maryland Eastern Shore, Princess Anne, MD
David Clark, University of Maryland Eastern Shore, Princess Anne, MD
Corrie Cotton, University of Maryland Eastern Shore, Princess Anne, MD
Fawzy Hashem, University of Maryland Eastern Shore, Princess Anne, MD
Richard Stonebraker, U.S. Department of Agriculture-ARS, Beltsville, MD
Kathryn White, U.S. Department of Agriculture-ARS, Beltsville, MD
Patricia Millner, U.S. Department of Agriculture-ARS, Beltsville, MD
Audio File Recorded Presentation
Introduction: Proposed U.S. FDA standards for untreated biological soil amendments stipulate a 9-month waiting period between soil application and harvest to reduce the risk of pathogen contamination on fresh produce. Manure, soil type, and initial bacterial populations may impact survival of bacterial pathogens and risk of produce contamination.  

Purpose: To compare population dynamics of non-pathogenic Escherichia coli (gEc) and attenuated E. coli O157:H7 (attEc) strains in surface and 15-cm cores of soils amended with untreated animal manure.

Methods: A multi-strain inocula of gEc and attEc containing low (LC) and high (HC) populations (5.3x104 and 3.8x106 CFU/m2), respectively, were surface-sprayed onto conventional and organic field plots (2m2) amended with poultry litter (PL), dairy-manure solids (DS), horse manure (HM), or no manure (NM). Manure was tilled into the soil in half the plots. Survival in surface and 15-cm core (tilled plot) samples was determined over 180 days post-inoculation (dpi) by colony count or MPN procedure.

Results: With few exceptions, LC- and HC-manured soil populations (surface and core) of gEc were reduced from 2.7-3.5 log CFU/g and 3.3-5.4 log CFU/g, respectively, to <1.0 log MPN/g by 7-28 dpi. Populations of gEc from HC-PL in conventional and organic soils survived up to 120-150 dpi and to 90 dpi in LC-PL before declining to <1.0 log MPN/g, respectively. Populations in HC-HM and HC-DS did not fall to <1.0 log MPN/g until 56 and 90 dpi, respectively. Populations of attEc consistently declined more rapidly than those of gEc in the same treatments, and attEc never resuscitated to >1.0 log MPN/g as did gEc.

Significance: Conventional and organic soil amended with PL consistently prolonged survival of both gEc and attEc compared to soils amended with DS, HM, or NM. Population declines for gEc generally were moderated in surface compared to core soils, but attEc populations were very similar in surface and core soils.

Back to: Technical Session - Microbial Food Spoilage, Food Toxicology, Dairy and Other Food Commodities, Produce
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