Listeria monocytogenes has emerged as a food safety concern for a number of produce commodities. While L. monocytogenes contamination can occur throughout the supply chain, contamination from the packinghouse environment represents a particular challenge and has been linked to recalls. This study aimed to investigate the prevalence, persistence, and diversity of Listeria monocytogenes (LM) and other Listeria species (LS) in produce packinghouses. A longitudinal study was performed in 11 packinghouses (commodities included micro-green, peach, apple, tomato, broccoli, cauliflower, and cucumber) in three US states. In each packinghouse, 34 to 46 sites representing zones 2-4 were selected and swabbed. Packinghouses were visited 4 times and samples were processed for Listeria by US Food and Drug Administration's Bacteriological Analytical Manual methods. Presumptive Listeria-positive isolates were confirmed by PCR. Species and allelic type (AT) were identified by sigB sequencing. Among the 1,584 samples tested, 3.2%, 2.7%, and 0.6% of the samples were positive for LM, LS, and both LM and LS, respectively. Five different species of Listeria were identified with L. monocytogenes being the most prevalent species. A high AT diversity (0.95 Simpson's Diversity Index) was observed amongst Listeria isolates. There were 15 instances of Listeria repeated isolation (site testing positive ≥2 times). Upon analysis of subtype data, only 3 sites tested positive for the same Listeria AT >2 times. Data showed in this longitudinal study that Listeria prevalence and persistence in packinghouses was low (e.g., <4% prevalence). Therefore, sanitation program development and implementation in packinghouses are critical to limit Listeria harborage and residence. / Master of Science in Life Sciences / Listeria monocytogenes is one of the deadliest foodborne pathogens, accounting for about 20% of the deaths caused by foodborne illnesses in the US. Historically, L. monocytogenes has been a big concern for Ready-to-Eat products (ice cream, deli meats, etc.), but in the last decade, there have been several listeriosis outbreaks associated with fresh produce (e.g. cantaloupes, apples, celery, packaged salad) becoming a produce safety concern. Some of these outbreaks have been traced back to the produce farm (pre-harvest) and the operations after harvesting (post-harvest). Though there is research focusing on the prevalence of Listeria in the pre-harvest environment, there is a need for studies investigating Listeria at the post-harvest level. This research project, focused on gaining a better understanding of the prevalence, persistence, and diversity of Listeria (including L. monocytogenes) in produce packinghouses. 11 packinghouses facilities were sampled four times during the packing season. The samples were obtained from different stationary (e.g. walls, drains, floors) and moving (e.g. bins, forklifts, pallets) non-food contact surfaces and equipment during operation hours. Isolates were processed to detect and isolate Listeria species (including L. monocytogenes). Listeria isolates were confirmed and fingerprinted. Listeria prevalence in these packinghouses was low (6.4%), and it varied among packinghouses. Drains, cold storages, and wet non-food contact surfaces were the sites with the highest Listeria prevalence. There were 3 cases of Listeria repeated isolation (same Listeria detected in the same site in at least 2 of the 4 visits). The diversity of Listeria in these packinghouses was high. The information gathered through this research provides a better understanding of where and what species of Listeria can be found in a produce packinghouse iv facility. This knowledge may be used to develop and implement mitigation strategies and interventions to control and/or reduce the risk of Listeria contamination in produce packinghouses.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/89919 |
| Date | 10 June 2019 |
| Creators | Estrada, Erika M. |
| Contributors | Food Science and Technology, Strawn, Laura K., Williams, Robert C., Moreno Switt, Andrea I. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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