Thesis
Molecular subtyping of E. coli O157 and Salmonella spp. isolated from an organic farming environment and examination of laboratory methods to isolate Salmonella spp. from soil
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/103006
Abstract
Produce foodborne outbreaks have emphasized the need to understand routes of pathogen transmission in farming systems and identify reliable detection methods. Studies examined pathogen contamination within an organic farming system and compared conventional Salmonella spp. isolation methods in non-sterile soil. First, a two-year study examined prevalence and genetic relatedness of E. coli O157 and Salmonella spp. isolated from soil amendments (broiler litter, turned pile and mixed feedstock, aerated static pile compost), pastured sheep, irrigation water, soil and produce (lettuce, spinach, squash, and radishes). During year 1, the highest prevalence of E. coli O157 was observed in irrigation water samples (7.5%) with 2.5% positive for Salmonella spp. From year 1 to year 2, the prevalence of E. coli O157 and Salmonella spp. in irrigation water decreased by 4.4% and 1.5%, respectively. E. coli O157 was isolated from lettuce (4.5%) and squash (5.8%) in year 1 but was not isolated from produce in year 2. Lower pathogen prevalence between years in produce may have been influenced by the farm switching from overhead to drip irrigation from year 1 to year 2. Genetic relatedness among pathogens was determined using pulsed-field gel electrophoresis (PFGE). Soil isolate banding patterns indicated potential relationships between irrigation water isolates and pastured animal influences. Furthermore, lettuce isolate banding patterns indicated potential relationships with irrigation water and soil isolates. Several sources within an organic farming system could contribute to the presence of E. coli O157 and Salmonella spp. Secondly, the FDA's Bacteriological Analytical Manual (method 1) was compared to the Brilliant Green Agar method (method 2) and the CHROMagar method (Method 3) for the detection of Salmonella spp. in soil collected from an organic farming system. Non-sterile soil samples were separately inoculated with four Salmonella serovars (S. Enteriditis, S. Mbrandaka, S. Anatum, and S. Heidelberg) at inoculation levels ranging from 0.45-2.82 log CFU/g. Methods 1 and 3 yielded a sensitivity of 100% while method 2 yielded a sensitivity of 97%, indicating that the CHROMagar method is a promising alternative to the FDA's BAM method for the detection of Salmonella spp. in soil.
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Details
- Title
- Molecular subtyping of E. coli O157 and Salmonella spp. isolated from an organic farming environment and examination of laboratory methods to isolate Salmonella spp. from soil
- Creators
- Caleb James
- Contributors
- Karen M. Killinger (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Food Science, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525061001842
- Language
- English
- Resource Type
- Thesis