Persistence of Escherichia coli O157:H7 and Listeria monocytogenes on the exterior of three common food packaging materials

An estimated 179 million cases of acute gastroenteritis (AGE) occur each year in the United States. Escherichia coli O157:H7 and Listeria monocytogenes, common etiologic agents of AGE, both have low-infectious doses and high environmental resistance. Surfaces contaminated with either pathogen, such as the exterior surface of a food package, could serve as a vehicle for AGE transmission. The aim of this study was to determine the persistence of E. coli O157:H7 and L. monocytogenes on three common food packaging materials-oriented polyethylene terephthalate (OPET), oriented polypropylene (OPP), and nylon-6. Coupons (5 x 5 cm(2)) from each material were sterilized under ultraviolet light for 5 min, inoculated with ca. 7 log CFU of a three-strain-mixture of green fluorescent protein (GFP)-labeled E. coli O157:H7, then incubated according to the Technical Association of the Pulp and Paper Industry standards. Surviving E. coli O157:H7 cells were recovered in saline at 0, 0.25, 0.5, 1, 2, 3, 5, 7, 14, 15 days then enumerated on tryptic soy broth (TSB) supplemented with ampicillin using the three-tube most probable number (MPN) method. The same procedure using a three-strain mixture of rifampin-resistant (Rif)-L. monocytogenes was followed except TSB was supplemented with rifampin. E. coli O157:H7 and L. monocytogenes both survived on OPET, OPP, and nylon-6 for 15 days. The log reductions for E. coli O157:H7 were 5.7 log MPN, 5.3 log MPN, and 5.1 log MPN across the three materials respectively. The log reduction for L. monocytogenes was 6.5 log MPN, 6.3 log MPN, and 4.8 log across the same three materials. The number of surviving E. coli cells was significantly higher (P > 0.05) than L. monocytogenes at sampling times 1, 2, 3, 5, 7, 14, and 15 days. No significant difference was shown between the two bacteria between 0 and 0.5 days. Survival of both bacteria across all three materials was not significantly different (P > 0.05). These results suggest that a highly contaminated (10(7) CFU/coupon) exterior surface of a food package could be a potential vehicle for the transmission of bacteria associated with AGE.