Enterococcus faecalis is a robust bacterium and, to survive within GIT, Ivacaftor has to cope with various stresses such as acid pH, nutrient limitation and deleterious effects of bile. In addition, the ability of the cell to survive in a wide range of environments as well as its intrinsic resistance

to chemical and physical stresses and antibiotics favour E. faecalis prevalence in an over-medicated environment (Michaux et al., 2011). The capacity of E. faecalis to cause disease is based on the presence of some major virulence factors but is also fine-tuned by many subtle virulence/fitness factors. Several transcriptional regulators have already been shown to be correlated with virulence and stress response, e.g. Fsr, EtaRS, CylR, HypR, PerR, SigV and Ers (Qin et al., 2001; Gilmore et al., 2002; Teng et al., 2002; Verneuil et al., 2004, 2005; Riboulet-Bisson et al., 2008; Le Jeune et al., 2010a). We recently characterized the transcriptional regulator SlyA (Ef_3002) of E. faecalis. Using the Galleria mellonella model it has been shown that the

ΔslyA mutant is more virulent than the wild-type strain. PARP assay In addition, ΔslyA survives better in macrophages and has a greater ability to persist in organs of mice (liver and kidneys) (Michaux et al., 2011). DNA microarray experiments revealed that 117 genes were deregulated in the ΔslyA mutant compared to the parental strain, and that SlyA acts as a repressor and activator (Michaux et al., 2011). In this study, we attempt to find stress conditions that affect the transcription of slyA. Among several stresses tested corresponding to agents potentially encountered in GIT or during the infection process, we found that bile salts induced expression of slyA. Moreover, the growth of ΔslyA mutant was more affected in its growth when bile salts are present, in comparison Atazanavir with the parental strain. In addition, RT-qPCRs were performed to

identify new SlyA-regulated genes. The E. faecalis strains and plasmids used in this work are listed in Table 1. Routinely, cells were grown without shaking at 37 °C in M17 medium supplemented with 0.5% glucose (GM17). Growth of the wild-type, ΔslyA, and complemented strain was examined for several environmental variables. Overnight cultures were diluted in fresh GM17 to an OD600 nm of 0.1. Growth was examined under the following conditions: 0.08% bile salts, 2 mM H2O2, 2% ethanol, growth under agitation with glycerol as the sole energy source (which induces an intracellular oxidative stress; Bizzini et al., 2010), pH 5.5, elevated temperatures (45, 50 and 55 °C), 20 mg mL−1 lysozyme, and growth in horse serum and human urine. Cultures were incubated until an OD600 nm of 0.5 and harvested after 30 min of exposition to stresses mentioned above or after 3 h in serum or urine.