Local Farmers Market Fresh Produce Sampling for the Presence of

E. coli and Salmonella Alexandra Kossik, Senior, Molecular, Cellular, and Developmental Biology & Public Health, University of Washington

Environmental Health Research Experience Program John Scott Meschke, Nicola Beck, Amy Leang, Department of Environmental & Occupational Health Sciences

Foodborne disease in humans is an ever present problem and recently fresh produce, in particular lettuce and tomatoes, have been linked to several significant outbreaks. • In Washington State, vendors selling fresh whole unprocessed produce directly to

consumers at local farmers markets are not mandated to obtain a license from the health department or have their goods inspected by the state, whereas farmers selling to grocery stores or other conventional retailers are required to complete these additional steps.

• This project looked at a total of fifty-five samples of fresh produce, including both heads of lettuce and tomatoes, which were collected weekly from five local farmers markets in the greater Seattle-Metro area to estimate the presence of Escherichia coli and Salmonella.

Introduction

Materials and Methods • When possible the produce samples were not excessively handled and remained unwashed prior

to running each respective assay. Produce was stored at 4°C from time of purchase until assayed (usually <24hrs).

• Samples designated for E. coli testing were first eluted in PBS and then assayed using the Colilert system and IDEXX QuantiTray 2000 to check for color change and fluorescence. Salmonella was seen through elution in Universal Pre-Enrichment broth followed by overnight incubation in Tetrathionate broth, and later streaked on XLD agar plates.

Conclusion and Discussion

Results

Acknowledgments and References This poster was supported by Award Number R25ES16150 from the National Institute of Environmental Health Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. 1) "Growing On the Swan Slough." Hanging at the Farmers Market, 9 June 2012. Web. 06 Aug. 2012. <http://growingontheswanslough.blogspot.com/2012/06/hanging-at-farmers-market.html>. 2) "Bayview Farmers Market." Bayview Farmers Market Archive, 30 May 2010. Web. 06 Aug. 2012. <http://bayviewfarmersmarket.blogspot.com/2010_05_01_archive.html>.

Lettuce samples were generally found to have a greater presence of both E. coli and Salmonella when compared to the tomatoes. However, PCR analysis will be completed to confirm these suspected Salmonella colonies. An overwhelming majority of the E. coli samples showed evidence of total fecal coliforms based on their change in IDEXX tray color. This could be due to varying types of environmental contamination, though the stage at which this occurs is unknown. Contamination could possibly happen during planting, farming, harvesting, processing, or even shipping of the produce. Other routes could include the irrigation water, type of manure, type of vendor, as was seen with organic farmers, and even infected workers handling the food. Results of this study indicate that both E. coli and Salmonella are present in farmers market produce samples, which could encourage a push for stricter standards for vendors selling in these markets.

• Twenty-three of the thirty-five lettuce samples had enumerable E. coli, ranging from 1 to 756 CFU/100ml, while only one tomato had enumerable E. coli.

• For Salmonella twenty-three percent of the fifty-three samples grew up with one or more black colonies, indicating presumptive positives for Salmonella [eleven lettuce and one tomato sample].

• The reproducibility between duplicate samples was fair, of fifteen sets of duplicates, thirteen had less than 3 CFU/100ml difference between E. coli samples, though the Salmonella results did not show the same reliability.

E. coli – Day 1 • Weigh out, bag, 150ml PBS, massage

5mins • Add Colilert, pour into IDEXX tray, seal,

incubate overnight

E. coli – Day 2 • Read results based on color change and

UV fluorescence

Salmonella – Day 1 • Weigh out, bag, add 150ml UP broth,

massage 5mins • Stand 1hr, adjust pH, incubate overnight

Salmonella – Day 2 • Add 1ml of each sample to 10ml of TT broth

• Vortex and incubate overnight

Salmonella – Day 3 • Vortex, streak with 3mm loop on XLD agar

plates • Incubate 24hrs.

Salmonella – Day 4 • Examine plates for black colonies

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Sampling Distribution

E.coli Tomato

E.coli Lettuce

Salmonella Tomato

Salmonella Lettuce

E.Coli Positive Salmonella Positive

Organic Farms 57.14% 28.57%

Non-Organic Farms 41.67% 21.74%

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A. Bag of 50 grams of lettuce prior to massaging for 5 minutes. B. Bag of 50 grams of lettuce after massaging for 5 minutes.

XLD plate of Salmonella sample. Yellow halo is possible growth of E. coli while black heads in centers of colonies would be presumptive

Salmonella.

IDEXX trays post incubation under UV light. Fluorescence demonstrated E. coli presence while color change portrays total

coliforms.

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Salmonella Results

Positive Tomato

Total Tomato Samples

Positive Lettuce

Total Lettuce Samples

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E. coli Results

Fluorescence Tomato

Color Change Tomato

Fluorescence Lettuce

Color Change Lettuce

Fluorescence = E. coli Color Change = Total Coliforms

Salmonella colonies

E. coli colonies