Prevalence of <i>Listeria</i> Species on Food Contact Surfaces in Washington State Apple Packinghouses

Abstract

The 2014 caramel apple listeriosis outbreak was traced back to cross-contamination between food contact surfaces (FCS) of equipment used for packing and fresh apples. For Washington state, the leading apple producer in the United States with 79% of its total production directed to the fresh market, managing the risk of apple contamination with <i>Listeria monocytogenes</i> within the packing environment is crucial. The objectives of this study were to determine the prevalence of <i>Listeria</i> spp. on FCS in Washington state apple packinghouses over two packing seasons and to identify those FCS types with the greatest likelihood to harbor <i>Listeria</i> spp. Five commercial apple packinghouses were visited quarterly over two consecutive year-long packing seasons. A range of 27 to 50 FCS were swabbed at each facility to detect <i>Listeria</i> spp. at two sample times, (i) postsanitation and (ii) in-process (3 h of packinghouse operation), following a modified protocol of the FDA's <i>Bacteriological Analytical Manual</i> method. Among 2,988 samples tested, 4.6% (<i>n</i> = 136) were positive for <i>Listeria</i> spp. Wax coating was the unit operation from which <i>Listeria</i> spp. were most frequently isolated. The FCS that showed the greatest prevalence of <i>Listeria</i> spp. were polishing brushes, stainless steel dividers and brushes under fans/blowers, and dryer rollers. The prevalence of <i>Listeria</i> spp. on FCS increased throughout apple storage time. The results of this study will aid apple packers in controlling for contamination and harborage of <i>L. monocytogenes</i> and improving cleaning and practices for sanitation of the FCS on which <i>Listeria</i> spp. are the most prevalent.<b>IMPORTANCE</b> Since 2014, fresh apples have been linked to outbreaks and recalls associated with postharvest cross-contamination with the foodborne pathogen <i>L. monocytogenes</i> These situations drive both public health burden and economic loss and underscore the need for continued scrutiny of packinghouse management to eliminate potential <i>Listeria</i> niches. This research assesses the prevalence of <i>Listeria</i> spp. on FCS in apple packinghouses and identifies those FCS most likely to harbor <i>Listeria</i> spp. Such findings are essential for the apple-packing industry striving to further understand and exhaustively mitigate the risk of contamination with <i>L. monocytogenes</i> to prevent future listeriosis outbreaks and recalls.