title: Thermal and Starvation Stress Response of Escherichia coli O157:H7 Isolates Selected from Agricultural Environments.
abstract: Pathogens exposed to agricultural production environments are subject to multiple stresses that may alter their survival under subsequent stress conditions. The objective of this study was to examine heat and starvation stress response of Escherichia coli O157:H7 strains isolated from agricultural matrices. Seven E. coli O157:H7 isolates from different agricultural matrices-soil, compost, irrigation water, and sheep manure-were selected, and two ATCC strains were used as controls. The E. coli O157:H7 isolates were exposed to heat stress (56°C in 0.1% peptone water for up to 1 h) and starvation (in phosphate-buffered saline at 37°C for 15 days), and their survival was examined. GInaFiT freeware tool was used to perform regression analyses of the surviving populations. The Weibull model was identified as the most appropriate model for response of the isolates to heat stress, whereas the biphasic survival curves during starvation were fitted using the double Weibull model, indicating the adaptation to starvation or a resistant subpopulation. The inactivation time during heating to achieve the first decimal reduction time (δ) calculated with the Weibull parameters was the highest (45 min) for a compost isolate (Comp60A) and the lowest (28 min) for ATCC strain 43895. Two of the nine isolates (ATCC 43895 and a manure isolate) had β < 1, indicating that surviving populations adapted to heat stress, and six strains demonstrated downward concavity (β > 1), indicating decreasing heat resistance over time. The ATCC strains displayed the longest δ2(>1,250 h) in response to starvation stress, compared with from 328 to 812 h for the environmental strains. The considerable variation in inactivation kinetics of E. coli O157:H7 highlights the importance of evaluating response to stress conditions among individual strains of a specific pathogen. Environmental isolates did not exhibit more robust response to stress conditions in this study compared with ATCC strains.
authors.affiliation: School of Food Science, Washington State University, P.O. Box 646376, Pullman, Washington 99164-6376.|School of Nutrition and Food Sciences, Louisiana State University AgCenter, 263 Knapp Hall, Baton Rouge, Louisiana 70803-6202.
authors.forename: Achyut
authors.initials: A
authors.lastname: Adhikari
authors.affiliation: Washington State University Puyallup Research and Extension Center, 2606 West Pioneer Avenue, Puyallup, Washington 98371.
authors.forename: Andy
authors.initials: A
authors.lastname: Bary
authors.affiliation: Washington State University Puyallup Research and Extension Center, 2606 West Pioneer Avenue, Puyallup, Washington 98371.
authors.forename: Craig
authors.initials: C
authors.lastname: Cogger
authors.affiliation: School of Food Science, Washington State University, P.O. Box 646376, Pullman, Washington 99164-6376.
authors.forename: Caleb
authors.initials: C
authors.lastname: James
authors.affiliation: School of Food Science, University of Idaho, 875 Perimeter Drive, Moscow, Idaho 83844-2312, USA.
authors.forename: Gülhan
authors.initials: G
authors.lastname: Ünlü
authors.affiliation: School of Food Science, Washington State University, P.O. Box 646376, Pullman, Washington 99164-6376.
authors.forename: Karen
authors.initials: K
authors.lastname: Killinger
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D015169:Colony Count, Microbial; D019453:Escherichia coli O157; D006358:Hot Temperature; D008372:Manure; D012756:Sheep
chemical_list: D008372:Manure
keywords: Environmental isolates; Escherichia coli O157:H7; Heat stress response; Starvation stress response; Weibull model