Tracking Microbial Contamination in Retail Environments Using Fluorescent Powder - A Retail Delicatessen Environment Example

Summary

The overall goal of this study was to demonstrate the potential cross contamination mechanism of foodborne pathogen Listeria monocytogenes in a retail deli setting. This methodology may be applied to a variety of different environments to track pathogen contamination.  

Abstract

Cross contamination of foodborne pathogens in the retail environment is a significant public health issue contributing to an increased risk for foodborne illness. Ready-to-eat (RTE) processed foods such as deli meats, cheese, and in some cases fresh produce, have been involved in foodborne disease outbreaks due to contamination with pathogens such as Listeria monocytogenes. With respect to L. monocytogenes, deli slicers are often the main source of cross contamination. The goal of this study was to use a fluorescent compound to simulate bacterial contamination and track this contamination in a retail setting. A mock deli kitchen was designed to simulate the retail environment. Deli meat was inoculated with the fluorescent compound and volunteers were recruited to complete a set of tasks similar to those expected of a food retail employee. The volunteers were instructed to slice, package, and store the meat in a deli refrigerator. The potential cross contamination was tracked in the mock retail environment by swabbing specific areas and measuring the optical density of the swabbed area with a spectrophotometer. The results indicated that the refrigerator (i.e. deli case) grip and various areas on the slicer had the highest risk for cross contamination. The results of this study may be used to develop more focused training material for retail employees. In addition, similar methodologies could also be used to track microbial contamination in food production environments (e.g. small farms), hospitals, nursing homes, cruise ships, and hotels.

Introduction

Cross contamination of foodborne pathogens in the food preparation environment, especially in the retail section, is a major concern due to an increased risk of foodborne illness from a variety of sources including the meats as well as the vegetables^1-5. Most often, bacterial pathogens enter the retail environment through contaminated food products⁶. Ready-to-eat foods prepared at the retail level are of particular concern as there is usually no further intervention or treatment (i.e. cooking or heating) prior to consumption⁷. Moreover, pathogens present on contaminated RTE food can then be transferred to other food products o....

Protocol

1. Standard Curve

1. Weigh 37.5 mg fluorescent powder and dissolve in 6 ml 200 proof ethanol. Make 2-fold serial dilutions of this solution in 200 proof ethanol.
2. Vortex all the samples for 10 sec and measure the absorbance at 370 nm.
3. Calculate the amount of fluorescent powder per 1 ml 200 proof ethanol.
4. Prepare the standard curve (concentration in mg/ml on the y-axis and absorbance at 370 nm on the x-axis) to demonstrate the absorbance based on fluorescent powder concentration.

2. Inoculate Deli Meat (Bologna) with Fluorescent Powder

1. Cut the deli meat into approximately 100 mm thick ....

Results

Figure 1 represents the areas of the slicer that were swabbed after the volunteers completed the tasks assigned. The volunteers were videotaped to analyze the average frequency of hand contact on these various surfaces. The frequency of hand contact was analyzed by four different observers and averaged. These results are demonstrated in Figure 2. The data shows that the meat grip, deli meat wrapper, deli meat, and deli paper had the highest rates of hand contact (average of 8-14 contacts.......

Discussion

The overall goal of this study was to demonstrate how bacterial cross contamination could occur in a retail deli environment in order to develop strategies to control and reduce the risk of foodborne illness. The retail deli environment has an especially high risk for L. monocytogenes contamination. The USDA-FSIS reported that deli meat sliced at the retail store has a seven times higher association with listeriosis that deli meat sliced and packaged at a federally inspected plant⁹.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Glo Germ Powder	Glo Germ Co		Purchased from vendor
Ethanol	Sigma	E7023
Permanent markers	Sharpie		Purchased from stationary store
Gloves	VWR	82026-424
Deli Meat	NA	NA	Bologna Chub from regular grocery store
Cutting Board	NA	NA	A regukar kitchen cutting board
Knife	NA	NA	A regular kitchen knife
5 cm x 5 cm sterile templates	NA	NA	Aluminum foil templates cut into 5 cm x 5 cm templates and sterilized
15 ml Polypropylene centrifuge tubes	VWR	89039-664
Cotton swabs	Puritan	25-806
Glass cuvettes	VWR	470019-186
Vortex	VWR	58816-121
Flip camera	Flip Ultra HD	NA	Purchased online
Deli slicer	Bizerba	SE-12
Deli refrigerator	True Company	TDBD-722
Scale		NA
Spectrophotometer	Milton Roy Company	NA	Spectronic 20D