{"id":{"repo_id":"washington","oai_identifier":"oai:digital.lib.washington.edu:1773/23403"},"canonical_url":"https://search.dev.ndltd.org/etd/washington/oai:digital.lib.washington.edu:1773/23403","repository":{"repo_id":"washington","name":"University of Washington","base_url":"https://digital.lib.washington.edu/server/oai/request"},"display":{"title":"Prevalence of Salmonella and E. coli on Produce from Seattle Farmers Markets","abstract":"This study surveyed the extent of microbial contamination on lettuce and tomatoes purchased from farmers markets, an increasingly popular source of local produce. Foodborne outbreaks in the U.S. have implicated <italic>Salmonella</italic> and <italic>E. coli</italic> as etiologic agents associated with raw produce-related illness; lettuce and tomatoes in particular have been implicated as common vehicles for <italic>Salmonella</italic> and <italic>E. coli</italic>. 126 samples of lettuce and tomatoes were collected from 5 major farmers markets in the Seattle metropolitan area throughout the 2012 summer/fall harvest season. Samples were analyzed for surface contamination of <italic>Salmonella spp.</italic> and generic <italic>E. coli</italic> as an indicator for fecal contamination. Whole tomato and 50 g lettuce samples were enriched or eluted in sterile Whirl-Pak® bags. Surfaces of samples were manually rubbed in liquid media to aid in removal of surface attached particles. Samples were pre-enriched in Universal Pre-enrichment Broth for the detection of <italic>Salmonella spp.</italic>, followed by selective enrichment with Tetrathionate (TT) broth and plating onto XLD agar for isolation. Presumptive colonies were confirmed with API and qPCR targeting the <italic>Salmonella</italic> invA gene. Rapid Colilert® tests, paired with Quanti-Tray®/2000 (IDEXX), were adapted for qualitative and quantitative detection of generic <italic>E. coli</italic> on produce. Following elution with phosphate buffered saline (PBS), positive wells were enumerated after 24 hrs and <italic>E. coli</italic> levels expressed as MPN/100 mL per sample. No <italic>Salmonella</italic> was detected; presumptive <italic>Salmonella</italic> isolates were confirmed to be <italic>Citrobacter</italic>. <italic>Escherichia coli</italic>, indicating fecal contamination, was present on 62% of lettuce and 6.4% of tomatoes samples. No significant differences were found in <italic>E. coli</italic> contamination by sampling date or between organic and conventional production methods. There were significantly more lettuce samples contaminated with <italic>E. coli</italic> than tomatoes (<italic>p</italic> < .05). This was the first study investigating the extent of microbial contamination on farmers markets produce in the United States. Results from this study and other fresh produce surveys indicate a low baseline occurrence of <italic>Salmonella</italic> on farmers markets produce. However, good agricultural practices should be promoted to reduce levels of <italic>E. coli</italic> indicating fecal contamination on produce.","abstract_html":"This study surveyed the extent of microbial contamination on lettuce and tomatoes purchased from farmers markets, an increasingly popular source of local produce. Foodborne outbreaks in the U.S. have implicated &lt;italic&gt;Salmonella&lt;/italic&gt; and &lt;italic&gt;E. coli&lt;/italic&gt; as etiologic agents associated with raw produce-related illness; lettuce and tomatoes in particular have been implicated as common vehicles for &lt;italic&gt;Salmonella&lt;/italic&gt; and &lt;italic&gt;E. coli&lt;/italic&gt;. 126 samples of lettuce and tomatoes were collected from 5 major farmers markets in the Seattle metropolitan area throughout the 2012 summer/fall harvest season. Samples were analyzed for surface contamination of &lt;italic&gt;Salmonella spp.&lt;/italic&gt; and generic &lt;italic&gt;E. coli&lt;/italic&gt; as an indicator for fecal contamination. Whole tomato and 50 g lettuce samples were enriched or eluted in sterile Whirl-Pak® bags. Surfaces of samples were manually rubbed in liquid media to aid in removal of surface attached particles. Samples were pre-enriched in Universal Pre-enrichment Broth for the detection of &lt;italic&gt;Salmonella spp.&lt;/italic&gt;, followed by selective enrichment with Tetrathionate (TT) broth and plating onto XLD agar for isolation. Presumptive colonies were confirmed with API and qPCR targeting the &lt;italic&gt;Salmonella&lt;/italic&gt; invA gene. Rapid Colilert® tests, paired with Quanti-Tray®/2000 (IDEXX), were adapted for qualitative and quantitative detection of generic &lt;italic&gt;E. coli&lt;/italic&gt; on produce. Following elution with phosphate buffered saline (PBS), positive wells were enumerated after 24 hrs and &lt;italic&gt;E. coli&lt;/italic&gt; levels expressed as MPN/100 mL per sample. No &lt;italic&gt;Salmonella&lt;/italic&gt; was detected; presumptive &lt;italic&gt;Salmonella&lt;/italic&gt; isolates were confirmed to be &lt;italic&gt;Citrobacter&lt;/italic&gt;. &lt;italic&gt;Escherichia coli&lt;/italic&gt;, indicating fecal contamination, was present on 62% of lettuce and 6.4% of tomatoes samples. No significant differences were found in &lt;italic&gt;E. coli&lt;/italic&gt; contamination by sampling date or between organic and conventional production methods. There were significantly more lettuce samples contaminated with &lt;italic&gt;E. coli&lt;/italic&gt; than tomatoes (&lt;italic&gt;p&lt;/italic&gt; &lt; .05). This was the first study investigating the extent of microbial contamination on farmers markets produce in the United States. Results from this study and other fresh produce surveys indicate a low baseline occurrence of &lt;italic&gt;Salmonella&lt;/italic&gt; on farmers markets produce. However, good agricultural practices should be promoted to reduce levels of &lt;italic&gt;E. coli&lt;/italic&gt; indicating fecal contamination on produce.","abstract_has_math":false,"creators":["Leang, Amy"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Meschke, John S"],"committee_chairs":[],"committee_members":[],"year":2013,"date_issued":"2013-07-25","date_published":"2013-07-25","updated_at":"2026-07-24T05:58:16Z","subjects":["E. coli; farmers market; pathogen; produce; Salmonella; Seattle"],"languages":["en_US"],"rights":["Copyright is held by the individual authors."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1773/23403","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Meschke, John S"]},{"key":"dc:creator","label":"Author","values":["Leang, Amy"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2013-07-25T17:49:03Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2013-07-25T17:49:03Z"]},{"key":"dc:date.issued","label":"Date","values":["2013-07-25"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["E. coli; farmers market; pathogen; produce; Salmonella; Seattle"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en_US"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright is held by the individual authors."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["Leang_washington_0250O_11796.pdf"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1773/23403"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Thesis (Master's)--University of Washington, 2013"]},{"key":"dc:description.abstract","label":"Abstract","values":["This study surveyed the extent of microbial contamination on lettuce and tomatoes purchased from farmers markets, an increasingly popular source of local produce. Foodborne outbreaks in the U.S. have implicated <italic>Salmonella</italic> and <italic>E. coli</italic> as etiologic agents associated with raw produce-related illness; lettuce and tomatoes in particular have been implicated as common vehicles for <italic>Salmonella</italic> and <italic>E. coli</italic>. 126 samples of lettuce and tomatoes were collected from 5 major farmers markets in the Seattle metropolitan area throughout the 2012 summer/fall harvest season. Samples were analyzed for surface contamination of <italic>Salmonella spp.</italic> and generic <italic>E. coli</italic> as an indicator for fecal contamination. Whole tomato and 50 g lettuce samples were enriched or eluted in sterile Whirl-Pak® bags. Surfaces of samples were manually rubbed in liquid media to aid in removal of surface attached particles. Samples were pre-enriched in Universal Pre-enrichment Broth for the detection of <italic>Salmonella spp.</italic>, followed by selective enrichment with Tetrathionate (TT) broth and plating onto XLD agar for isolation. Presumptive colonies were confirmed with API and qPCR targeting the <italic>Salmonella</italic> invA gene. Rapid Colilert® tests, paired with Quanti-Tray®/2000 (IDEXX), were adapted for qualitative and quantitative detection of generic <italic>E. coli</italic> on produce. Following elution with phosphate buffered saline (PBS), positive wells were enumerated after 24 hrs and <italic>E. coli</italic> levels expressed as MPN/100 mL per sample. No <italic>Salmonella</italic> was detected; presumptive <italic>Salmonella</italic> isolates were confirmed to be <italic>Citrobacter</italic>. <italic>Escherichia coli</italic>, indicating fecal contamination, was present on 62% of lettuce and 6.4% of tomatoes samples. No significant differences were found in <italic>E. coli</italic> contamination by sampling date or between organic and conventional production methods. There were significantly more lettuce samples contaminated with <italic>E. coli</italic> than tomatoes (<italic>p</italic> < .05). This was the first study investigating the extent of microbial contamination on farmers markets produce in the United States. Results from this study and other fresh produce surveys indicate a low baseline occurrence of <italic>Salmonella</italic> on farmers markets produce. However, good agricultural practices should be promoted to reduce levels of <italic>E. coli</italic> indicating fecal contamination on produce."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Prevalence of Salmonella and E. coli on Produce from Seattle Farmers Markets"]}]}],"canonical_facts":{"dc:contributor.advisor":["Meschke, John S"],"dc:creator":["Leang, Amy"],"dc:date.accessioned":["2013-07-25T17:49:03Z"],"dc:date.available":["2013-07-25T17:49:03Z"],"dc:date.issued":["2013-07-25"],"dc:description":["Thesis (Master's)--University of Washington, 2013"],"dc:description.abstract":["This study surveyed the extent of microbial contamination on lettuce and tomatoes purchased from farmers markets, an increasingly popular source of local produce. Foodborne outbreaks in the U.S. have implicated <italic>Salmonella</italic> and <italic>E. coli</italic> as etiologic agents associated with raw produce-related illness; lettuce and tomatoes in particular have been implicated as common vehicles for <italic>Salmonella</italic> and <italic>E. coli</italic>. 126 samples of lettuce and tomatoes were collected from 5 major farmers markets in the Seattle metropolitan area throughout the 2012 summer/fall harvest season. Samples were analyzed for surface contamination of <italic>Salmonella spp.</italic> and generic <italic>E. coli</italic> as an indicator for fecal contamination. Whole tomato and 50 g lettuce samples were enriched or eluted in sterile Whirl-Pak® bags. Surfaces of samples were manually rubbed in liquid media to aid in removal of surface attached particles. Samples were pre-enriched in Universal Pre-enrichment Broth for the detection of <italic>Salmonella spp.</italic>, followed by selective enrichment with Tetrathionate (TT) broth and plating onto XLD agar for isolation. Presumptive colonies were confirmed with API and qPCR targeting the <italic>Salmonella</italic> invA gene. Rapid Colilert® tests, paired with Quanti-Tray®/2000 (IDEXX), were adapted for qualitative and quantitative detection of generic <italic>E. coli</italic> on produce. Following elution with phosphate buffered saline (PBS), positive wells were enumerated after 24 hrs and <italic>E. coli</italic> levels expressed as MPN/100 mL per sample. No <italic>Salmonella</italic> was detected; presumptive <italic>Salmonella</italic> isolates were confirmed to be <italic>Citrobacter</italic>. <italic>Escherichia coli</italic>, indicating fecal contamination, was present on 62% of lettuce and 6.4% of tomatoes samples. No significant differences were found in <italic>E. coli</italic> contamination by sampling date or between organic and conventional production methods. There were significantly more lettuce samples contaminated with <italic>E. coli</italic> than tomatoes (<italic>p</italic> < .05). This was the first study investigating the extent of microbial contamination on farmers markets produce in the United States. Results from this study and other fresh produce surveys indicate a low baseline occurrence of <italic>Salmonella</italic> on farmers markets produce. However, good agricultural practices should be promoted to reduce levels of <italic>E. coli</italic> indicating fecal contamination on produce."],"dc:format.mimetype":["application/pdf"],"dc:identifier.other":["Leang_washington_0250O_11796.pdf"],"dc:identifier.uri":["http://hdl.handle.net/1773/23403"],"dc:language.iso":["en_US"],"dc:rights":["Copyright is held by the individual authors."],"dc:subject":["E. coli; farmers market; pathogen; produce; Salmonella; Seattle"],"dc:title":["Prevalence of Salmonella and E. coli on Produce from Seattle Farmers Markets"],"dc:type":["Thesis"]},"updated_at":"2026-07-24T05:58:16Z"}