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J Appl Microbiol. 2014 Feb;116(2):335-49. doi: 10.1111/jam.12373. Epub 2013 Nov 13.

Examination of factors for use as potential predictors of human enteric pathogen survival in soil.

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  • 1Department of Food Science and Technology, Center for Food Safety, Griffin, GA, USA.
  • 2Department of Crops and Soil Science, University of Georgia, Griffin, GA, USA.

Abstract

AIMS:

Three soils that varied in their physicochemical characteristics and microbial diversity were inoculated with Escherichia coli O157:H7 and Salmonella to determine the relative impact of abiotic and biotic factors on the pathogens' survival when the soil was held at 25°C.

METHODS AND RESULTS:

Three soils that were classified as having low, medium and high microbial diversity were divided into two batches for adjustment to 20% of water-holding capacity and to 40% of water-holding capacity. Soils were inoculated with both green fluorescent-labelled E. coli O157:H7 and red fluorescent-labelled Salmonella (5 log CFU g(-1) dry weight) and held at 25°C. Pathogens inoculated into an acidic soil died off within 9 weeks, whereas they were still detected in the other two soils by enrichment culture after 18 weeks. Moisture did not affect inactivation of E. coli O157:H7, but did affect Salmonella inactivation in soil having the greatest organic load and microbial diversity. Using multiple linear regression analysis, 98.7% of the variability in the inactivation rate for E. coli O157:H7 was explained by a model that included the variables of initial pH and electrical conductivity. Salmonella's inactivation rate was predicted by a model that included pH and initial cell numbers of copiotrophic and oligotrophic bacteria.

CONCLUSION:

This study provided evidence of specific properties that impact inactivation of E. coli O157:H7 and Salmonella in soils at 25°C.

SIGNIFICANCE AND IMPACT OF THE STUDY:

Identification of factors influential in the die-off of enteric pathogens will assist in developing guidelines for safe intervals between field contamination events and planting or harvesting of fresh-cut produce crops.

© 2013 The Society for Applied Microbiology.

KEYWORDS:

E. coli O157:H7; Salmonella; microbial diversity; soil

[PubMed - indexed for MEDLINE]
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