ORIGINAL ARTICLE Transcriptional analysis of virulence-related genes in enterococci from distinct origins A.R. Carlos 1 , T. Semedo-Lemsaddek 1 , M.T. Barreto-Crespo 2 and R. Tenreiro 1 1 Universidade de Lisboa, Faculdade de Cie ˆ ncias, Centro de Biodiversidade, Geno ´mica Integrativa e Funcional (BioFIG), Edifı´cio ICAT, Campus da FCUL, Campo Grande, Lisboa, Portugal 2 Instituto de Biologia Experimental e Tecnolo ´ gica (IBET) and Instituto de Tecnologia Quı ´mica e Biolo ´ gica Universidade Nova de Lisboa (ITQB-UNL), Qta do Marque ˆ s, Oeiras, Portugal Introduction Enterococci have been described as extremely hardy micro-organisms capable of inhabiting environments with a wide range of temperatures (10 and 45°C), pH values (4Æ6 and 9Æ6) and NaCl concentrations (up to 6Æ5%). Because of this high adaptability, they can be found in soil, water, plants and the gastrointestinal tracts of humans and animals. Although usually viewed as commensals, they are now acknowledged as opportunistic pathogens responsible for a broad variety of diseases, namely, bacteraemia, endocarditis, urinary tract infections and surgical wound infections (Jett et al. 1994; Seno et al. 2005; Stevens and Edmond 2005; Shaked et al. 2006). Enterococcal pathogenic potential is greatly increased because of their intrinsic and acquired resistance against several antimicrobial agents (Moellering and Krogstad 1979; Eliopoulos et al. 1988; Wade and Uttley 1996) and highly efficient ability to transfer genetic material (Clewell 1990). Enterococcus faecalis is considered responsible for nearly 80% of the infections, while Enterococcus faecium accounts for the majority of the remainder but other species have been increasingly reported as causes of human infection (Higashide et al. 2005; Iaria et al. 2005). Although a concern as human pathogens, these bacteria also play a beneficial role in the development of sensory characteristics of fermented foods, such as traditional cheeses produced in Mediterranean countries (Tsakalidou et al. 1993; Desmasures et al. 1997; Mannu et al. 1999; Keywords clinical strains, enterococci, food strains, RT-PCR, virulence-related genes. Correspondence Teresa Semedo-Lemsaddek, Faculdade de Cie ˆncias da Universidade de Lisboa, Edifı´cio ICAT, Campus da FCUL, Campo Grande, 1749-016 Lisboa, Portugal. E-mail: tmsemedo@fc.ul.pt 2009 ⁄ 0556: received 24 March 2009, revised and accepted 25 August 2009 doi:10.1111/j.1365-2672.2009.04551.x Abstract Aims: The role of enterococci in food fermentation and as probiotics counter- acts with their increasing importance as human pathogens. Over the years, several virulence factors have been described, mainly in clinical strains but also in food isolates. However, differential expression of such traits may modulate the pathogenic potential of the harbouring enterococci. To further unravel such differential response, this study aims to identify environmental cues responsible for triggering the expression of virulence-related genes. Methods and Results: The differential expression of eight virulence-related genes (cylMBAI, agg, esp, efaA fs and efaAfm) in 16 enterococci from distinct origins, grown in conditions simulating environmental colonization and infec- tion sites, was analysed by reverse transcriptase PCR. The expression profiles were environmental and strain-dependent, because no constant response was observed neither for clinical nor food enterococci. Conclusions: Virulence expression profiles are strain-specific and unrelated with strain’s origin or species allocation. Significance and Impact of the Study: The current study constitutes the first approach aimed at the evaluation of the differential expression of enterococcal virulence-related genes combining so many growth environments, enterococcal species and origins. So, with this investigation, we intend to contribute to the clarification of enterococcal pathogenicity potential, especially for food strains. Journal of Applied Microbiology ISSN 1364-5072 ª 2009 The Authors Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 108 (2010) 1563–1575 1563