Persistence of Escherichia coli O157:H7 on Commonly Used Food Packaging Materials

Introduction:  Escherichia coli O157:H7 causes many foodborne disease outbreaks in the United States. Because of its low infectious dose (<10 cells), contaminated surfaces, such as the outside of a food package, could be a source for disease transmission.

Purpose: Our aim was to determine persistence of E. coli O157:H7 on three food packaging materials: oriented polyethylene terephthalate (OPET), oriented polypropylene (OPP), and nylon 6.

Methods: Coupons (25 cm²) from each material were sterilized under ultraviolet light for five minutes. Spot and spread inoculation was performed on treatment coupons with ca. seven log CFU of a three strain mixture of green fluorescent protein (GFP)-labeled E. coli O157:H7. All were incubated as per Technical Association of the Pulp and Paper Industry (TAPPI standards: 23°C temperature; 50% relative humidity). Surviving E. coli O157:H7 cells, on duplicate coupons, were recovered in saline at selected time intervals (0, 0.25, 0.5, 1, 2, 3, 5, 7, 14, and 15 days) and enumerated on tryptic soy broth + ampicillin, using the three tubes most probable number (MPN) method described in the Bacteriological Analytical Manual. Day 30 coupons were enriched in tryptic soy broth + ampicillin. Isolated colonies were confirmed using the latex agglutination method. The experiment was performed in triplicate.

Results: GFP-labeled E. coli O157:H7 survived on OPET, OPP, and nylon 6 for over two weeks. Survival of E. coli O157:H7 rapidly decreased until day two on OPET (7.38±0.33 log MPN to 4.40±0.31 log MPN), OPP (7.50±0.41 log MPN to 3.83±0.64 log MPN), and nylon 6 (7.34±0.52 log MPN to 4.12±0.37 log MPN). The survival of E. coliO157:H7 on all three materials was not significantly different.

Significance: Escherichia coli O157:H7 survived for over two weeks on OPET, OPP, and nylon 6, suggesting the outer surface of a food package could be a potential fomite.