Laboratory Re-enactment of Storage Practices of Older Adults to Determine Potential Implications for Growth of Listeria monocytogenes

Older adults are particularly susceptible to listeriosis, and many frequently consume ready-to-eat (RTE) foods associated with Listeria monocytogenes. Consequently, safe storage of RTE-food is essential to reduce the risks of listeriosis. This study aimed to re-enact domestic food-storage malpractices of older adult consumers in a laboratory, to assess the potential impact on L. monocytogenes. Observed and self-reported data relating to domestic food-storage malpractices included prolonged storage of RTE foods and/or refrigeration temperatures exceeding recommendations (> 5.0°C). Re-enactment was performed using soft-cheese and RTE meat inoculated with ~3.7 log CFU L. monocytogenes, stored at recommended temperatures (2.5°C) (n = 110); temperatures exceeding recommendations (7.8°C) (n = 110), and ambient temperature (19.5°C) (n = 55). Samples were analyzed every 24 h for up to 21 days. Results indicated that L. monocytogenes grew at all storage temperatures. Average generation times indicated slower growth of L.monocytogenes at 2.5°C (94 h t-1) than at either 7.8°C(21.5 h t-1) or 19.5°C (11 h t-1), suggesting that prolonged storage of RTE foods resulted in increased L. monocytogenes populations (< 7.6 log CFU/g), potentially making such foods unsafe for consumption. Findings indicate that storage practices contrary to consumer recommendations, which are intended to reduce the risk of foodborne disease, increase L. monocytogenes populations, thus increasing the potential for foodborne disease.