Environmental monitoring for <i>Listeria</i> species in controlled atmosphere apple storage facilities

Studies have revealed the presence of Listeria species on food and non-food contact surfaces in apple packing facilities. However, the occurrence of Listeria in controlled atmosphere (CA) storage facilities has not been well characterized. This two-year longitudinal study assessed the prevalence, diversity, and distribution of Listeria spp. within nine CA storage rooms at three different facilities (A, B, and C), focusing on Zone 3 non food contact surfaces. A total of 304 samples were collected, and 5.9% (18) were positive for Listeria spp., predominantly on floors below condenser units. Of 18 positive sample sites, Listeria monocytogenes was the main species detected, accounting for 61.1% (11/18), followed by Listeria seeligeri at 22.2% (4/18). None of the facilities showed repeated detection of the same Listeria subtype at the same location during the two-year period. However, in Facility A, L. monocytogenes was repeatedly detected on the floor below condenser units, although the isolates belonged to different subtypes. Our findings highlight the importance of preventive measures such as environmental monitoring and sanitation programs that may mitigate Listeria spp. contamination in CA storage environments, considering the microbes ability to survive in low temperature modified atmosphere conditions conducive to long-term apple storage.