Prevalence of Listeria spp. on food contact surfaces in commercial cherry packinghouses in Washington and California.

Recent recalls for tree fruit due to possible contamination with Listeria monocytogenes have highlighted the importance of understanding the high-risk food contact surfaces (FCS) in commercial packinghouses in order to manage the risk of cross-contamination within the packing environment. The objectives of this study were to determine the prevalence of Listeria spp. on FCS in Washington State and California cherry packinghouses and to identify locations with the greatest likelihood to harbor Listeria spp. Four commercial cherry packinghouses were visited three times each during two consecutive packing seasons in Washington, and four commercial packinghouses were visited up to three times during one packing season in California. A total of 40 FCS were swabbed for Listeria spp. at each facility during each visit at two intra-day sampling timepoints: (i) post-sanitation but pre-packing and (ii) during packing. Swabs were processed following a modified protocol of the FDA's Bacteriological Analytical Manual method. In Washington, 2.0% (38/1920) of FCS were positive, while 2.4% (15/636) were positive in California for Listeria spp. Across both states, the FCSs that showed the greatest prevalence of Listeria spp. were bristle flaps, solid conveyor belts, and singulators, with combined prevalence of 5.7% (12/209), 4.7% (9/192), and 3.8% (6/154), respectively. The prevalence of Listeria spp. also varied depending on processing stage (i.e., receiving vs. sorting vs. packing) and intra-day timepoints (i.e., post-sanitation/pre-packing vs during packing). Study findings will help cherry packinghouses in mitigating the risk of cross-contamination and harborage of Listeria spp. in packing environments.