title: Fate of Listeria monocytogenes , Pathogenic Yersinia enterocolitica , and Escherichia coli O157:H7 gfp+in Ready-to-Eat Salad during Cold Storage: What Is the Risk to Consumers?
abstract: In this study, we investigated the fate of Listeria monocytogenes , pathogenic Yersinia enterocolitica , and Escherichia coli O157:H7 gfp+inoculated in low numbers into ready-to-eat baby spinach and mixed-ingredient salad (baby spinach with chicken meat). Samples were stored at recommended maximum refrigerator temperature (8°C in Sweden) or at an abuse temperature (15°C) for up to 7 days. Mixed-ingredient salad supported considerable growth when stored at 15°C during shelf life (3 days), with populations of L. monocytogenes , pathogenic Y. enterocolitica , and E. coli O157:H7 gfp+increasing from less than 2.0 log CFU/g on day 0 to 7.0, 4.0, and 5.6 log CFU/g, respectively. However, when mixed-ingredient salad was stored at 8°C during shelf life, only L. monocytogenes increased significantly, reaching 3.0 log CFU/g within 3 days. In plain baby spinach, only pathogenic Y. enterocolitica populations increased significantly during storage for 7 days, and this was exclusively at an abuse temperature (15°C). Thus, mixing ready-to-eat leafy vegetables with chicken meat strongly influenced levels of inoculated strains during storage. To explore the food safety implications of these findings, bacterial numbers were translated into risks of infection by modeling. The risk of listeriosis (measured as probability of infection) was 16 times higher when consuming a mixed-ingredient salad stored at 8°C at the end of shelf life, or 200,000 times higher when stored at 15°C, compared with when consuming it on the day of inoculation. This indicates that efforts should focus on preventing temperature abuse during storage to mitigate the risk of listeriosis. The storage conditions recommended for mixed-ingredient salads in Sweden (maximum 8°C for 3 days) did not prevent growth of L. monocytogenes in baby spinach mixed with chicken meat. Manufacturers preparing these salads should be aware of this, and recommended storage temperature should be revised downwards to reduce the risk of foodborne disease.
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. Box 7036, SE-750 07, Uppsala, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Söderqvist
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. Box 7036, SE-750 07, Uppsala, Sweden.|Research and Development Department, National Food Agency, P.O. Box 622, SE-751 26, Uppsala, Sweden.
authors.forename: Susanne Thisted
authors.initials: ST
authors.lastname: Lambertz
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. Box 7036, SE-750 07, Uppsala, Sweden.
authors.forename: Ivar
authors.initials: I
authors.lastname: Vågsholm
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. Box 7036, SE-750 07, Uppsala, Sweden.
authors.forename: Lise-Lotte
authors.initials: LL
authors.lastname: Fernström
authors.affiliation: Department of Biosystems and Technology, Microbial Horticulture Unit, P.O. Box 103, SE-230 53, Alnarp, Sweden.
authors.forename: Beatrix
authors.initials: B
authors.lastname: Alsanius
authors.affiliation: Department of Biosystems and Technology, Microbial Horticulture Unit, P.O. Box 103, SE-230 53, Alnarp, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Mogren
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. Box 7036, SE-750 07, Uppsala, Sweden.
authors.forename: Sofia
authors.initials: S
authors.lastname: Boqvist
mesh_terms: D003080:Cold Temperature; D015169:Colony Count, Microbial; D019453:Escherichia coli O157; D005516:Food Microbiology; D006801:Humans; D008089:Listeria monocytogenes; D013548:Sweden; D013696:Temperature; D015008:Yersinia enterocolitica
keywords: Baby spinach; Deli salad; Growth potential; Leafy vegetables; Mixed-ingredient salad; Temperature abuse