Listeria monocytogenes in Vacuum-Packed Smoked Fish Products: Occurrence, Routes of Contamination, and Potential Intervention Measures Restituto Tocmo, Katja Krizman, Wei Jie Khoo, Li Kai Phua, Minjeong Kim, and Hyun-Gyun Yuk Abstract: The occurrence of Listeria monocytogenes in ready-to-eat (RTE) fish products is well documented and represents an important food safety concern. Contamination of this pathogen in vacuum-packed (VP) smoked fish products at levels greater than the RTE food limit (100 CFU/g) has been traced to factors such as poor sanitary practices, contaminated processing environments, and temperature abuse during prolonged storage in retail outlets. Intervention technologies including physical, biological, and chemical techniques have been studied to control transmission of L. monocytogenes to these products. High-pressure processing, irradiation, and pulsed UV-light treatment have shown promising results. Po- tential antilisterial effects of some sanitizers and combined chemical preservatives have also been demonstrated. Moreover, the concept of biopreservation, use of bioactive packaging, and a combination of different intervention technologies, as in the hurdle concept, are also under consideration. In this review, the prevalence, routes of contamination, and potential intervention technologies to control transmission of L. monocytogenes in VP smoked fish products are discussed. Introduction In the last 3 decades, international fish trade increased from US$8 billion in 1976 to a record export value of US$102.5 bil- lion in 2010 (FAO 2012). Along with this increase in demand for fish products at the international market, the seafood industry has faced growing concern about the safety of these commodities. The safety of consuming ready-to-eat (RTE) vacuum-packed (VP) smoked fish products, in particular, has drawn scrutiny from the public and the scientific community as these products have been associated with listeriosis outbreaks (EFSA 2009; CDC 2013). In fact, smoked fish has been one of the seafood commodities incrim- inated since Listeria monocytogenes was recognized as a foodborne pathogen in 1981 (FAO 2012). L. monocytogenes, a Gram-positive and facultative anaerobe re- sponsible for listeriosis, is thought to contaminate fish products mainly during the processing phase (Tompkin 2002). Since this microorganism is widely present in the environment and can grow in a wide range of temperature, its entry into the processing plant can occur in many ways. Consumption of foods that con- tain infectious levels of this invasive pathogen may cause serious illness in individuals with weakend immune system and in preg- nant women (Norton and others 2001). The Foodborne Disease MS 20131141 Submitted 08/14/2009, Accepted 11/14/2003. Authors are with Food Science & Technology Programme, Dept. of Chemistry, Natl. Univ. of Singapore, 3 Science Drive 3, Singapore, 117543. Direct inquiries to author Yuk (E-mail: chmyukhg@nus.edu.sg). Outbreak Surveillance System of the Centers for Disease Control and Prevention (CDC) in the United States reported 9 confirmed listeriosis outbreaks in 2009 to 2010 which resulted in 49 outbreak- associated illnesses, 40 hospitalizations, and 9 deaths (CDC 2013). In the European Union (EU), L. monocytogenes contamination in gravad and smoked fish is among the highest in RTE foods (EFSA 2011). According to Uyttendale and others (2009), smoked fish products packaged under vacuum are high-risk seafood products because L. monocytogenes thrives well in them. VP smoked fish products are kept under chilled temperatures to extend shelf-life and facilitate longer storage and distribution. However, L. monocy- togenes being a psychrotrophic organism can grow at 4 ◦ C and may proliferate to infective levels during improper storage. The main safety concern with RTE VP smoked fish products is that people consume them without prior heating or additional cooking (Kin and others 2012). Nowadays, consumers worldwide demand high-quality and safe food products. In reponse this changing demand, the seafood in- dustry has been finding practical ways to ensure safety and quality of VP smoked fish products. Vacuum-packaging, the final step employed in the manufacture of smoked fish products, is a non- thermal processing technique that provides consumers products with good organoleptic and nutritional properties and is often combined with refrigeration to prolong shelf-life and enable dis- tribution of products even to international markets (Phillips 1996). Prior to packaging, smoking is carried out to preserve fish prod- ucts and impart a characteristic flavor (Neunlist and others 2005). In the manufacture of smoked fish, smoking is often carried out in 172 Comprehensive Reviews in Food Science and Food Safety  Vol. 13, 2014 C  2014 Institute of Food Technologists ® doi: 10.1111/1541-4337.12052