The effects of temperature, chlorine and acids on the survival of Listeria and Salmonella strains associated with uncooked shrimp carapace and cooked shrimp flesh M.N. Wan Norhana a, b , Susan E. Poole c , Hilton C. Deeth a , Gary A. Dykes d, * a School of Land, Crop and Food Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia b Fisheries Research Institute, 11960, Batu Maung, Penang, Malaysia c Queensland Primary Industries and Fisheries, Hamilton, Queensland 4007, Australia d CSIRO Nutritional and Food Sciences, PO Box 3312, Tingalpa DC, Queensland 4173, Australia article info Article history: Received 25 August 2009 Received in revised form 12 October 2009 Accepted 13 October 2009 Available online 17 October 2009 Keywords: Shrimp Listeria Salmonella Chlorine Heat Acid abstract The purpose of this study was to assess the influence of the association of Listeria and Salmonella with shrimp surfaces on the effects of temperature, chlorine and acids on their survival. Planktonic, attached and colonized cells of Listeria monocytogenes Scott A, L. monocytogenes V7, Salmonella Senftenberg 1734b and S. Typhimurium ATCC 14028 were challenged with high (50  , 60  and 70  C) and low (4  C) temperature, 100 ppm sodium hypochlorite solution, and acetic, hydrochloric and lactic acids (pH 4.0). Attached and colonized Listeria and Salmonella showed significantly greater (p < 0.05) resistance to heat (w1.3–2.6 fold increase in D-values), hypochlorite (w6.6  40.0 fold) and acids (w4.0–9.0 fold) than their planktonic counterparts. There were no significant differences (p > 0.05) in the survival of planktonic, attached or colonized cells of Listeria and Salmonella stored under refrigerated conditions. The association of Listeria and Salmonella with shrimp surfaces enhances their resistance to heat, chlorine and acids. Both attachment to, and subsequent colonization of, shrimp surfaces by pathogens may reduce the efficacy of methods used in their control. Strategies to reduce attachment of these pathogens to shrimp are required to assure safety of this product. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. 1. Introduction Shrimp and shrimp products, including ready-to-eat (RTE) shrimp, can support the survival and/or growth of bacterial food- borne pathogens and there are reports of foodborne disease outbreaks where shrimps have been implicated (NACMCF, 2008). Furthermore, the presence of pathogens has also caused significant numbers of shrimp product detentions and recalls (Ababouch et al., 2005). Listeria and Salmonella are examples of pathogens that are commonly associated with shrimp. These pathogens have been regularly isolated from shrimp culture environments (Bhaskar and Sachindra, 2006) and at retail (Phan et al., 2005), and are also known to adapt to and persist in the product processing environ- ments in spite of regular sanitation procedures (Fonnesbech Vogel et al., 2001; Gudmundsdottir et al., 2006). The adaption to and persistence in the processing environments of these pathogens necessarily require them to be able to survive stressful conditions such as high and low temperature, acidic conditions, drying or disinfectant treatment. Although the exact nature of the mechanism of resistance of Listeria and Salmonella to adverse conditions is not completely understood it been suggested to be facilitated, at least in part, by bacterial attachment to and subsequent colonization of surfaces (Krysinski et al., 1992). Attached cells of Listeria and Salmonella have been demonstrated to be significantly more resistant to disinfec- tants (Dhir and Dodd, 1995; Frank and Koffi, 1990; Lee and Frank, 1991; McCarthy, 1992) and heat (Dhir and Dodd, 1995; Frank and Koffi, 1990; Lee and Frank, 1991) as compared to their planktonic counterparts. Dhir and Dodd (1995) for example detected an approximately 2-fold increase in D 52 values of S. Enteritidis attached to stainless steel and glass as compared to planktonic cells. A more than 10-fold increase in resistance to disinfectants (iodine, chlorine and quaternary ammonium compounds) of attached Listeria cells compared to the planktonic ones has also been reported (McCarthy, 1992). Non-chitinolytic Listeria and Salmonella have been demonstrated to be able to attach and colonize shrimp carapaces and tissue (Wan Norhana et al., 2009). However, to our knowledge there have been no reports on the ability of the attached and colonized Listeria and Salmonella to resist adverse conditions. * Corresponding author. Current address: School of Science, Monash University, Sunway Campus, PO Box 8975, 46780 Kelana Jaya, Selangor Darul Ehsan, Malaysia. Tel.: þ60 3 5514 4964; fax: þ60 3 5514 6364. E-mail address: gary.dykes@sci.monash.edu.my (G.A. Dykes). Contents lists available at ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm 0740-0020/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2009.10.008 Food Microbiology 27 (2010) 250–256