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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH PRODUCE

Location: Environmental Microbial and Food Safety Laboratory

Title: Comparative survival of Escherichia coli O157:H7, Salmonella Typhimurium, and Murine Norovirus on spinach plants

Authors
item Ferguson, Sean
item Roberts, Cheryl
item Handy, Eric
item Barak, Jeri -
item Kniel, Kali -
item Sharma, Manan

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 22, 2013
Publication Date: N/A

Technical Abstract: Introduction: Outbreaks resulting from the consumption of leafy greens contaminated with E. coli O157:H7, Salmonella spp., and norovirus have occurred. It is unclear how the stress response factor rpoS in E. coli O157:H7 and Salmonella spp. affects their survival on spinach. Purpose: A comparison of the survival of E .coli O157:H7, Salmonella Typhimurium, and murine norovirus (MNV) under the same conditions on spinach plants was performed. Materials and Methods: Five week-old spinach (Menorca, semi-savoy) plants were co-inoculated with 6 logCFU/plant of each of the following strains: wild-type (wtO157) E. coli O157:H7, wt S. Typhimurium (wtST), and rpoS-deficient mutants of wt E. coli O157:H7 (rpoSO157) and S. Typhimurium (rpoSST). MNV was inoculated on the same spinach plants at 10^6 PFU/plants. Wt and rpoS-deficient strains were enumerated from plant homogenates on selective media either directly or by MPN. Five plants per day were analyzed on days 0–4. The presence of MNV was also determined on day 0 and day 3. Results: Initial populations of all bacterial strains were 4.3 –4.5 logCFU/plant on day 0. Populations of wtST and wtO157 declined by 3.1 and 3.9 logCFU/plant, respectively; rpoSO157 and rpoSST declined by 3.9 and 4.7 logCFU/plant, respectively over 4 days. Populations of rpoSO157:H7 and rpoSST were 2 logCFU/plant lower than paired wtO157 and wtST on day 1. Populations of wtO157 strains were significantly (p< 0.05) higher than those of both rpoS-deficient strains on day 2 and significantly higher than wtST, rpoSO157, and rpoSST on day 3. MNV were assayed and recovered on day 0 and day 3. Significance: The rpoS gene may be more important to S. Typhimurium survival on spinach than E. coli O157:H7. Both wt and rpoS-deficient E. coli O157:H7 strains survived at higher populations than wt and rpoS-deficient S. Typhimurium. MNV persists for at least 3 days on the foliar surface of spinach plants.

Last Modified: 9/22/2014
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