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Pathogens 2014, 3(3), 528-548; doi:10.3390/pathogens3030528

Fitness of Outbreak and Environmental Strains of Escherichia coli O157:H7 in Aerosolizable Soil and Association of Clonal Variation in Stress Gene Regulation

Produce Safety and Microbiology Research Unit, United States Department of Agriculture, Agriculture Research Service, Western Regional Research Center, Albany, CA 94710, USA
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Received: 16 May 2014 / Revised: 20 June 2014 / Accepted: 24 June 2014 / Published: 30 June 2014
(This article belongs to the Special Issue Foodborne Pathogens)
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Abstract

Airborne dust from feedlots is a potential mechanism of contamination of nearby vegetable crops with Escherichia coli O157:H7 (EcO157). We compared the fitness of clinical and environmental strains of EcO157 in <45 µm soil from a spinach farm. Differences in survival were observed among the 35 strains with D-values (days for 90% decreases) ranging from 1–12 days. Strains that survived longer, generally, were from environmental sources and lacked expression of curli, a protein associated with attachment and virulence. Furthermore, the proportion of curli-positive (C+) variants of EcO157 strains decreased with repeated soil exposure and the strains that were curli-negative (C) remained C post-soil exposure. Soil exposure altered expression of stress-response genes linked to fitness of EcO157, but significant clonal variation in expression was measured. Mutations were detected in the stress-related sigma factor, rpoS, with a greater percentage occurring in parental strains of clinical origin prior to soil exposure. We speculate that these mutations in rpoS may confer a differential expression of genes, associated with mechanisms of survival and/or virulence, and thus may influence the fitness of EcO157. View Full-Text
Keywords: Escherichia coli O157:H7; curli; stress-response genes; environmental fitness; MLVA; adaptation; rpoS; slp; osmY; hdeA; nemR; marR; mutations Escherichia coli O157:H7; curli; stress-response genes; environmental fitness; MLVA; adaptation; rpoS; slp; osmY; hdeA; nemR; marR; mutations
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MDPI and ACS Style

Ravva, S.V.; Cooley, M.B.; Sarreal, C.Z.; Mandrell, R.E. Fitness of Outbreak and Environmental Strains of Escherichia coli O157:H7 in Aerosolizable Soil and Association of Clonal Variation in Stress Gene Regulation. Pathogens 2014, 3, 528-548.

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