Enterococcus faecalis has controversial status due to its emerging role in nosocomial infections, while some strains with beneficial effects are used as probiotics and starter cultures in dairy industry. These bacteria can be found as resident or transient germs in the gut or on skin, where they are continually exposed to various eukaryotic molecules. In this context, the aim of our work was to evaluate the effect of the catecholamine stress hormones, epinephrine (Epi), and norepinephrine (NE) on some Enterococcus s trains. Four E. faecalis strains were included in this study: E. faecalis MMH594 and E. faecalis V583, pathogenic strains of clinical origin, E. faecalis Symbioflor 1 clone DSM 16431, a pharmaceutical probiotic, and E. faecalis OB15, a probiotic strain previously isolated from Tunisian rigouta ( Baccouri et al., 2019 ). Epi was found to modulate the formation of biofilm (biovolume and thickness) in E. faecalis , whether pathogens or probiotics. NE had less effect on biofilm formation of these bacteria. We also investigated the effect of Epi and NE on adhesion of E. faecalis to eukaryotic cells as it is the first step of colonization of the host. Epi was found to significantly enhance the adhesion of MMH594 and OB15 to Caco-2/TC7 intestinal cells and HaCaT keratinocyte cells, whereas NE significantly increased the adhesion of V583 and Symbioflor 1 DSM 16431 to Caco-2/TC7 cells, the adhesion of MMH594, Symbioflor 1 DSM 16431, and OB15 to HaCaT cells. Analysis of a putative adrenergic sensor of Epi/NE in E. faecalis , compared to QseC, the Escherichia coli adrenergic receptor, allowed the identification of VicK as the nearest protein to QseC with 29% identity and 46% similarity values. Structure modeling and molecular docking of VicK corroborated the hypothesis of possible interactions of this putative adrenergic sensor with Epi and NE, with binding energies of −4.08 and −4.49 kcal/mol, respectively. In conclusion, this study showed for the first time that stress hormones could increase biofilm formation and adhesion to eukaryotic cells in E. faecalis . Future experiments will aim to confirm by in vivo studies the role of VicK as adrenergic sensor in E. faecalis probiotic and pathogen strains. This may help to develop new strategies of antagonism/competition in the gut or skin ecological niches, and to prevent the colonization by opportunistic pathogens.
Filamentous bacteriophages can become superinfective and infect P. aeruginosa , even though they are inserted in the genome as lysogens. Despite this productive infection, growth of the host is only mildly affected, allowing the study of the interaction between the phage and the host, which is not possible in the case of lytic phages killing rapidly their host.
Enterococcus faecalis OB15 is a probiotic strain that was isolated from rigouta, a popular traditional Tunisian fermented cheese. We report here the draft genome sequence of this strain, consisting of 2,912,159 bp, with an average GϩC content of 37.49%. E nterococcus faecalis is a Gram-positive, diplococcus-forming, catalase-positive, and facultative anaerobic bacterium with typical cream-colored colonies on MRS agar. This microorganism is ubiquitous in the environment; it is found mainly in the gastrointestinal tracts of humans and animals but is also widespread in soil, water, plants, and dairy products (1). Several strains are known to be opportunistic pathogens and are recognized among the major etiological agents of nosocomial and other human infections (endocarditis and urinary tract infections), due to their ability to acquire resistance to a wide range of antibiotics and the presence of virulence determinants (2, 3). In contrast, other strains have potential benefits for human health and are currently used as starter cultures in manufacturing cheese (4, 5), as bacteriocin (enterocins) producers in food preservation, and as potential probiotics in the food industry (1, 6).Recently, we isolated E. faecalis OB15 from rigouta, a popular traditional Tunisian fermented cheese that is often prepared by boiling acidified cheese whey from cow's milk (7). Physiological and genomic analyses demonstrated that E. faecalis OB15 has met all of the principle requirements for and has properties of an efficient probiotic and could be a reliable candidate for future use in the food or feed industry (7).Genomic DNA of E. faecalis OB15 was extracted from an overnight culture in MRS broth at 37°C, under static conditions, with the GeneJET genomic DNA purification kit (Thermo Fisher Scientific, France), following the manufacturer's recommendations. Extracted DNA was quantified using a Qubit fluorometer and the double-stranded DNA (dsDNA) high-sensitivity (HS) assay kit (Thermo Fisher Scientific). Libraries were prepared using the Nextera XT DNA sample kit (Illumina, San Diego, CA), and genomic sequencing was performed using a MiSeq instrument (Illumina) with a 2 ϫ 250-bp paired-end protocol (
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