Cross-contamination Risks in Reusable Grocery Shopping Bags

Introduction: 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 reusable bags tested were positive for Escherichia coli (E. coli).

Purpose: It is important to better understand the potential reusable bags pose in cross-contamination of foodborne pathogens. This study considered the potential of pathogen transfer from contaminated leafy greens to a reusable bag and survival on a reusable bag.

Methods: 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 (24 bags per treatment) and 30-minute transport was simulated using a large sample mixer. The microbial load of the reusable bags was measured one-hour after simulation and all bags were stored at 21°C. Three bags per treatment were tested on Day 1, 3, 5, 7, 9, 11, 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, yeast and mold, coliform, and E. coli O157:H7.

Results: One-hour after transport simulation and on Day 1, 10³ CFU/ml tetracycline and chloramphenicol resistant E. coli O157:H7 was recovered. Microbial loads from Day 3 to Day 14, 10¹ CFU/ml E. coli O157:H7 was consistently recovered. Counts were similar regardless of sampling location on the bag. Non-pathogenic microorganisms were recovered at low concentrations.

Significance: It is important to consider potential pathogens available for transfer to reusable bags and further food products. 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.