Cross-Contamination Risks in Reusable Grocery Shopping Bags and Potential Risks to Patrons: A Model Applied to Leafy Greens E. coli O157:H7
Allison Smathers, Benjamin Chapman, and Trevor Phister
Reusable polypropylene-grocery shopping bags have increased in popularity as a method to reduce environmental impact of plastic one-use bags. In 2010, researchers found eight percent of used-reusable bags tested were positive for Escherichia coli (E. coli). It is important to better understand the potential reusable bags pose in cross-contamination of foodborne pathogens. First, this study focused on patron use of reusable grocery bags. Second, this study considered the potential of pathogen transfer from contaminated leafy greens to a reusable bag and survival on a reusable bag. In order to explore practices carried out by patrons with their reusable bags, 107 patrons participated in a convenience sample. Leafy greens were inoculated with 105 CFU/ml tetracycline and chloramphenicol resistant E. coli O157:H7. Inoculated and non-inoculated leafy greens were placed in reusable bags (21 bags per treatment) and 30-minute transport was simulated using a large sample mixer. The microbial load of the reusable bags was measured and all bags were stored at 21°C. Three bags per treatment were tested on Day 1, 3, 5, 8, 10, 12, and 14. Bags were sampled in five locations (10 x 10 cm), one on the bottom and four at varying levels on the side-panels of the bag, using wet swabs. Reusable bags were measured for aerobic plate count, coliform, and E. coli O157:H7. Two-hours after transport simulation and on Day 3, 103 CFU/ml tetracycline and chloramphenicol resistant E. coli O157:H7 was recovered. The microbial loads from Day 3 to Day 14 were minimal, 101 CFU/ml E. coli O157:H7 was consistently recovered. Counts were similar regardless of sampling location on the bag but were highest on the bottom location. Non-pathogenic microorganisms were recovered at low concentrations. It is important to consider potential pathogens available for transfer to reusable bags and further to food products that come in contact with contaminated bags. The data generated helps with the development of a better model for assessing microbial movement within reusable bags. The results of this study convey the potential for survival and cross-contamination of foodborne pathogens on reusable bags.
Allison Smathers, M.S.
Entrepreneurial Program Assistant
Department of Food, Bioprocessing, & Nutrition Sciences
North Carolina State University
sasmathe@ncsu.edu
Food Safety Culture Team 