Resistances to UV-C irradiation of Salmonella Typhimurium and Staphylococcus aureus in wet and dried suspensions on surface with egg residues Takashi Kuda a, * , Taichiro Iwase a , Yuphakhun Chaturongkasumrit a , Hajime Takahashi a , Takashi Koyanagi b , Bon Kimura a a Department of Food Science and Technology, Tokyo University of Marine Science and Technology, Konan, Minato-ku, Tokyo 108-8477, Japan b Department of Food Science, Ishikawa Prefectural University, Suematsu, Ishikawa 921-8836, Japan article info Article history: Received 2 June 2011 Received in revised form 2 August 2011 Accepted 9 August 2011 Keywords: Surface sediment Egg Salmonella Typhimurium Staphylococcus aureus UV-C abstract To clarify the effects of food sediments on ultraviolet-C (254 nm) sanitation in food-related environ- ments, we examined the resistance of pathogenic bacteria (Salmonella Typhimurium and Staphylococcus aureus) cells, in wet and dried suspensions adhered with 1.5e15% w/v egg albumen, 1.5e15% yolk or 3.0 e30% whole egg solutions, against UV-C irradiation. Bacterial suspensions (0.1 ml of 8 log CFU/ml) were put on 47 mm4 glass dishes and dried at room temperature (20e24  C) for 180 min in a bio safety cabinet with ventilation. Viable S. Typhimurium and S. aureus cells in distilled water decreased during the drying period from 7.2 to 3.2 and from 8.0 to 6.5 log CFU/dish, respectively,. On the other hand, the bacteria cells were protected from drying by egg compounds, even by the lowest concentration. The UV- C treatment (0.16 mW/cm 2 for 10 min) showed a clear bactericidal effect in the absence of egg compounds. However, the bactericidal effect was inhibited by 15% yolk and 30% whole egg. Results in this study suggested that the small food sediment protect bacteria on the surfaces from dryness and UV-C irradiation and it might introduce cross contamination. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Adhesion of microorganisms to equipment surfaces has the potential to transmit pathogens to food, and this is apparent in the food industry (Simões, Simões, & Vieirab, 2010) and in the domestic environment (Hayson & Sharp, 2005; Lund & Ormerod, 1995). It is known that microorganisms hide in the inner side and/or on wet surfaces of food and medical equipments often form biofilms that exhibit tolerance to various stresses (McNeill & Hamilton, 2004). In particular, there are many reports about the biofilms of Pseudo- monas aeruginosa (Bak, Ladefoged, Begovic, & Winding, 2010; Parsek & Tolker-Nielsen, 2008), S. aureus (Kwon et al., 2008), Lis- teria monocytogenes (Takahashi, Suda, Tanaka, & Kimura, 2010) and S. Typhimurium (Zaklkhany, Harrington, Nimtz, Hinton, & Römling, 2010), due to their strong resistance against disinfectants and their medical importance in disease, such as nosocomial infections. Salmonella is a well-documented pathogen known to occur in a wide range of foods, especially eggs and egg products (Rivoal et al., 2009). Most cases of human infection with S. enterica subsp. enterica serotype Enteritidis result from the consumption of contaminated raw eggs (Mead et al., 1999). Furthermore, salmo- nellosis caused by S. Typhimurium has remained relatively stable or increased in Europe, the US and the other countries (Weill & Grimont, 2005). Staphylococcus aureus is also a leading cause of gastroenteritis resulting from the consumption of contaminated foods. Staphylococcal food poisoning is due to the absorption of staphylococcal enterotoxins preformed in various foods, including eggs and egg products (Loir, Baron, & Gautier, 2003). Ultraviolet-C (254 nm) light treatment has been used widely in the food industries and hospitals for air and surfaces sanitation (Anderson, Bånrud, Bøe, Bjordal, & Drangsholt, 2006; Sommers, Sites, & Musgrove, 2010). Furthermore, UV-C irradiation also has been applied for pasteurization of water and liquid foods such as fruit juices, milk and egg albumen (Tran & Farid, 2004; Unluturk, Atilgan, Baysal, & Unluturk, 2010). It is considered that food elements protect microbial cells when the adhered cells are dried on the surfaces of food equipments used in food processing line (Leslie, Israeli, Lighthart, Crowe, & Crowe, 1995). We previously reported that a standard concentration (2 mg/ml) of surfactant- disinfectants did not decrease the number of bacterial cells dried on surfaces with milk and egg compounds (Kuda, Iwase, Takahashi, Koyanagi, & Kimura, 2011; Kuda, Yano, & Kuda, 2008). The * Corresponding author. Tel./fax: þ81 35 463 0602. E-mail address: kuda@kaiyodai.ac.jp (T. Kuda). Contents lists available at SciVerse ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont 0956-7135/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2011.08.018 Food Control 23 (2012) 485e490