M: Food Microbiology & Safety The Elimination of Listeria Monocytogenes Attached to Stainless Steel or Aluminum Using Multiple Hurdles Alexandria W. Mertz, Corliss A. O’Bryan, Philip G. Crandall, Steven C. Ricke, and Rub´ en Morawicki Abstract: Ready-to-eat luncheon meats sliced in retail delis have been found to pose the greatest risk of foodborne illness from Listeria monocytogenes among all ready-to-eat foods. Slicers used in delis have many removable parts that are connected with seals and gaskets, with spaces, cracks and crevices that are difficult to clean adequately and may provide a niche for L. monocytogenes survival. Standard cleaning and sanitizing practices used by deli employees may not eliminate Listeria in these niches. Moist heat is known to be more effective against L. monocytogenes than dry heat at the same temperature and time. The study reported here investigated the effects of moist heat combined with quaternary ammonium compounds (5 or 10 ppm), chlorine (10 or 25 ppm) or peracetic acid (10 or 25 ppm) on inactivating L. monocytogenes attached to stainless steel or aluminum coupons cut from commercial deli meat slicer components. All sanitizers when used alone resulted in a 2- to 3-log reduction of L. monocytogenes on stainless steel or aluminum surfaces, while moist heat alone resulted in a 3- to 4-log reduction. When combined with heat the quaternary ammonium was used at 5 ppm, peracetic acid at 10 ppm and chlorine at 10 ppm. When the 2 lethal treatments were combined there was a 5- to7-log reduction as compared to initial inoculation. Keywords: aluminum, chlorine, L. monocytogenes, peracetic acid, quaternary ammonia, stainless steel Practical Application: The results of this study will provide a better understanding and potential methods for the saniti- zation of industrial deli meat slicers. In turn, the knowledge gained from this study can reduce the risk of contamination and outbreaks of L. monocytogenes and other food-borne pathogens for consumers. Introduction Listeria monocytogenes is most frequently found residing on food processing equipment with small spaces and narrow openings, in- cluding slicing, dicing, packaging and brining machinery (Autio and others 1999, Lund´ en and others 2002). Deli meat slicers have been shown to harbor L. monocytogenes and provide for cross- contamination of meats and other materials sliced on these ma- chines (Gilbert 1969). The U.S. Food Safety Inspection Service (FSIS) and the U.S. Food and Drug Administration (FDA) per- formed a risk assessment of L. monocytogenes in retail foods to determine the likelihood of exposure to this organism from con- suming certain foods and the possible public health consequences (Kause 2009). During this risk assessment they determined that deli meats posed the greatest risk of exposure to L. monocytogenes (Kause 2009). Additionally, they determined that approximately 83% of listeriosis cases contracted from consuming luncheon meats could be attributed to deli meats sliced at a retail deli store as opposed to meats sliced at the manufacturer, packaged and sold (Kause 2009). In a study by Garrido and others (2009), 8.5% of samples of RTE meats sliced and packaged in retail stores were positive for pathogenic L. monocytogenes while only 2.7% of samples from meats commercially packaged tested positive, indicating that the prevalence of L. monocytogenes in store sliced deli meats is about 3 MS 20150423 Submitted 3/11/2015, Accepted 5/6/2015. Authors Mertz, O’Bryan, Crandall, Ricke, and Morawicki are with Dept. of Food Science, Univ. of Arkansas, Fayetteville, AR 72704, U.S.A. Authors O’Bryan, Crandall, and Ricke are with Center for Food Safety, Univ. of Arkansas, Fayetteville, AR 72704, U.S.A. Direct inquiries to author Morawicki (E-mail: rmorawic@uark.edu). times greater than in RTE luncheon meats sliced and packaged by the manufacturer. Slicers have many removable parts that are connected and sealed with gaskets which can become worn and degraded over time and with scrubbing with abrasive pads and heavy use of sanitizers. When these slicer parts become worn and pitted, spaces are created that allow food debris and moisture to become trapped. Since these spaces cannot be cleaned adequately, bacteria have an opportunity to multiply in these niches (Tarrant 2014). The uneven surface of the stainless steel also allows bacteria to effectively adhere and form biofilms (Stone and Zottola 1985). Microorganisms that are attached to surfaces in biofilms may be much more resistant to sanitizing compounds than planktonic cells (Joseph and others 2001: Kusumaningrum and others 2003: Ali and others 2006). The high resistance of cells in biofilms is due to the slower diffusion of the sanitizers and antimicrobial agents through the biofilm matrix, making it more difficult to reach the deeper layers of the biofilm and destroy imbedded pathogens (Krolasik and others 2010). Routine, proper cleaning and sanitizing procedures are recom- mended to prevent cross-contamination of food by deli slicers (Lin and others 2006). After routine cleaning, sanitizers may fail to completely eliminate microbial contamination because the deli employee did not receive proper training or did not follow proper cleaning protocols, the incorrect sanitizer was selected or it was not employed correctly (Neal 2013) or difficult-to-clean areas of the slicer were unable to be properly accessed (Vorst and others 2006). Chlorine is one of the most commonly used sanitizers in the food processing industry, but there are several reports that certain strains of L. monocytogenes can become tolerant to chlorine (El Kest and Marth 1988; Cordier and others 1989; Lund´ en and others 2003; C  2015 Institute of Food Technologists R  doi: 10.1111/1750-3841.12926 Vol. 80, Nr. 7, 2015  Journal of Food Science M1557 Further reproduction without permission is prohibited