Specific molecular detection of Carnobacterium piscicola SF668 in cold smoked salmon E. Pelle ´, X. Dousset, H. Pre ´vost and D. Drider Laboratoire de Microbiologie Alimentaire et Industrielle, ENITIAA, Nantes, France 2004/1095: received 20 September 2004, revised and accepted 15 December 2004 ABSTRACT E. PELLE ´ , X. DOUSSET, H. PRE ´ VOST AND D. DRIDER. 2005. Aims: To establish a rapid and reliable multiplex PCR (mPCR)-based method allowing specific identification of Carnobacterium piscicola SF668 during storage of cold smoked salmon (CSS). Methods and Results: CSS was inoculated with C. piscicola SF668 and stored at 4°C. Samples were withdrawn at regular time intervals and analysed by counting the number of viable cells. About 25–100% of colonies grown on Elliker plates were subjected to mPCR amplification. The results show that strains presumably identified as C. piscicola SF668 were predominant over the test period. Conclusions: mPCR is a powerful tool to study competitiveness of C. piscicola SF668, which inhibits the growth of Listeria monocytogenes. Significance and Impact of the Study: The present study demonstrates the importance of molecular methods in studying competitiveness of strains with potential food applications. Keywords: Carnobacterium piscicola SF668, cold smoked salmon, lactic acid bacteria, multiplex PCR. INTRODUCTION Studies on microbial ecology of cold smoked salmon (CSS) during storage have revealed the existence of a rich Gram- positive microbiota, which is composed of lactic acid bacteria (LAB; Lactobacillus curvatus, Lactobacillus sakei, Lactobacillus plantarum, Lactobacillus farciminis, Lactobacillus alimentarius, Carnobacterium piscicola, C. divergens) and Brochotrix thermosphacta (Truelstrup Hansen 1995; Leroi et al. 1998). To this intrinsic microbiota can also be added a spoilage microbiota rendered putatively pathogenic for human health by the presence of Listeria monocytogenes (Farber and Peterkin 1991; Johansson et al. 1999). The coexistence of natural and spoilage microbiota within CSS leads to antagonistic interactions and food competition allowing the development of one microbiota at the expense of the other one. Several reports pointed out listeriosis outbreaks caused by elevated number of Listeria monocyto- genes, a hardly, pathogenic bacterium common in the environment and difficult to control in foods. The effect- iveness of C. piscicola SF668 to control growth of Listeria monocytogenes in CSS has been recently examined (Brillet et al. 2004). Increasing applications of strains producing bacteriocins as natural food preservatives could be facilitated by the development and use of powerful molecular tools allowing specific detection of such type of strains. Thus, the aim of this study was to determine the competitiveness of C. piscicola SF668 among intrinsic LAB associated with the storage of CSS using a specific multiplex PCR (mPCR) set up in this work. MATERIALS AND METHODS Bacterial strains, media and growth conditions The specificity of the mPCR based on intergenic spacer region (ISR) and DNA coding for piscicolin 126 was tested on DNA isolated from the strains listed in Table 1. Carnobacterium strains were cultivated in Elliker broth (Biokar Diagnostics, Beauvais, France) or Elliker agar Correspondence to: D. Drider, Laboratoire de Microbiologie Alimentaire et Industrielle, ENTIAA, Rue de la Ge ´raudie `re, BP 82225, 44322 Nantes cedex 3, France (e-mail: drider@enitiaa-nantes.fr). ª 2005 The Society for Applied Microbiology Letters in Applied Microbiology 2005, 40, 364–368 doi:10.1111/j.1472-765X.2005.01696.x