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Stress Responses of Enterococci Yanick Auffray, Abdellah Benachour, Aurélie Budin-Verneuil, Jean-Christophe Giard, Axel Hartke, Vianney Pichereau, Alain Rincé, Nicolas Sauvageot, and Nicolas Verneuil

13.1 Introduction Enterococci are Gram-positive bacteria that fit within the general definition of lactic acid bacteria (Stiles and Holzapfel 1997). The genus Enterococcus is composed of species associated with animals and plants, but only those from humans and domestic animals have been studied in detail (Flahaut et al. 1997a). Enterococci are most often considered to be components of the intestinal flora of humans and animals and are generally searched for in wastewater and food products, where their detection may indicate the risk of the presence of enteropathogenic organisms. Once they leave the oro-fecal lifestyle, their survival is linked to their exceptional aptitude to resist or grow in hostile environments that are usually detrimental to the development of most mesophilic microorganisms. However, a certain ambiguity exists concerning their relationship with human beings. Indeed, some Enterococcus species or strains constitute a component of the microflora of fermented foods such as cheeses, sausages, green olives, and others that contributes to ripening and to the development of flavor (Foulquié Moreno et al. 2006). They also produce bacteriocins against pathogens such as Listeria and Clostridium (Cintas et al. 1998). This beneficial role led to the introduction of enterococci strains in starter cultures. Moreover, some strains of enterococci are used as probiotics to improve the microbial balance of the intestine and to treat gastroenteritis in humans and animals (Lewenstein et al. 1979; O’Sullivan et al. 1992). On the other hand, over the last two decades, enterococci, formerly viewed as organisms of minimal clinical impact, have emerged as important hospital-acquired pathogens in immunocompromised patients (Low et al. 1994; Morrison et al. 1997).

Y. Auffray (*) Laboratoire de Microbiologie de l’Environnement, USC INRA2017/EA UCBN956, Université de Caen, 14032 Caen Cedex, France e-mail: [email protected]

E. Tsakalidou and K. Papadimitriou (eds.), Stress Responses of Lactic Acid Bacteria, Food Microbiology and Food Safety, DOI 10.1007/978-0-387-92771-8_13, © Springer Science+Business Media, LLC 2011

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According to epidemiological data, enterococci rank among the top four pathogens responsible for nosocomial infections (Chenoweth and Schaberg 1990). Enterococcal infections include urinary tract infections, hepatobiliary sepsis, endocarditis, surgical wound infections, bacteremia, and neonatal sepsis (Poh et  al. 2006; de Fátima Silva Lopes et al. 2005). These data also indicate that Enterococcus faecalis is the most common species isolated from human illnesses, whereas Enterococcus faecium is linked with a higher threat of antibiotic resistance (Huycke et  al. 1998; Giraffa 2002). In fact, enterococci show intrinsic (chromosomal) resistance to cephalosporins, lincosamid