Is the production of the biogenic amines tyramine and putrescine a species-level trait in enterococci? Victor Ladero, María Fernández, Marina Calles-Enríquez, Esther Sánchez-Llana, Elena Cañedo, M. Cruz Martín, Miguel A. Alvarez * Instituto de Productos Lácteos de Asturias, IPLA-CSIC, Crta. de Infiesto s/n, Apdo. de Correos 85, 33300 Villaviciosa, Asturias, Spain article info Article history: Received 28 June 2011 Received in revised form 29 November 2011 Accepted 15 December 2011 Available online 22 December 2011 Keywords: Biogenic amines Tyramine Putrescine Enterococcus faecalis Enterococcus faecium Enterococcus durans Food safety abstract Biogenic amines (BA) are toxic nitrogenous compounds that can be accumulated in foods via the microbial decarboxylation of certain amino acids. Lactic acid bacteria (LAB) strains belonging to different species and genera have been described as BA producers and are mainly responsible for their synthesis in fermented foods. It is generally accepted that the capacity to produced BAs is strain-dependent. However, the large number of enterococci identified as BA producers suggests that the aminogenic trait may be a species-level characteristic. Enterococcus faecalis, Enterococcus faecium and Enterococcus durans strains of different origin were analysed to determine their capacity to produce tyramine and putrescine. The presence of the genes responsible for this and the identity of their flanking regions were checked by PCR. The results suggest that tyramine biosynthesis is a species-level characteristic in E. faecalis, E. faecium and E. durans. Putrescine synthesis was found to be a species-level trait of E. faecalis, with production occurring via the agmatine deamination pathway. Some E. faecium strains of human origin also produced putrescine; this trait was probably acquired via horizontal gene transfer. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Society is becoming increasingly aware of the importance of the diet in health, and is demanding dairy foods that are safer and of higher quality. These demands have motivated interest in the detailed characterization of the microbiota of dairy products. From a sensorial point of view, the control of amino acid catabolism is one of the key steps in ensuring their quality. This is also important in terms of food safety since some catabolic reactions can lead to the formation of toxic compounds such as biogenic amines (BA) (Fernández and Zúñiga, 2006; Linares et al., 2011), the consumption of which can lead to intoxication (Ladero et al., 2010a). BAs are low molecular weight nitrogenous compounds that are mainly formed by amino acid decarboxylation. Lactic acid bacteria (LAB) are the microorganisms mainly responsible for their synthesis in fer- mented food products, and strains of different species and genera have been described as BA producers (for a review see Linares et al., 2011). The pathways used to catabolise amino acids have traditionally been considered strain-level characteristics (Smit et al., 2005; Fernández and Zúñiga, 2006) including those related to BA formation (Lonvaud-Funel, 2001; Ancín-Azpilicueta et al., 2008). The genes coding for BA pathways are, in some cases, located on plasmids, which facilitate their acquisition (Lucas et al., 2005). Horizontal gene transfer has been proposed as one of the mecha- nisms by which the genetic background necessary for BA synthesis is acquired (Marcobal et al., 2006; Coton and Coton, 2009). However, the analysis of the data provided by different authors, and of the available genome sequences, suggests that in some cases the ability to produce BA is a species-level rather than a strain-level characteristic (Ladero et al., 2011b). For instance, using microbio- logical methods, more than 90% of Enterococcus faecium strains isolated from cheese have been identified as tyramine producers; similar results have been reported for Enterococcus faecalis and Enterococcus durans (Sarantinopoulos et al., 2001). These three Enterococcus species are those most commonly isolated from dairy products (Giraffa, 2003; Martín-Platero et al., 2009), and many strains have been described as tyramine- (Sarantinopoulos et al., 2001; Fernández et al., 2004; Komprda et al., 2008; Ladero et al., 2010a) or putrescine-producers (Llácer et al., 2007). Moreover, their presence has been related to the accumulation of BAs (Roig- Sagués et al., 2002; Ladero et al., 2010b); certainly, tyramine and putrescine are the most abundant BAs in fermented dairy products * Corresponding author. Tel.: þ34 985 89 21 31; fax: þ34 985 89 22 33. E-mail address: maag@ipla.csic.es (M.A. Alvarez). Contents lists available at SciVerse ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm 0740-0020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2011.12.016 Food Microbiology 30 (2012) 132e138