Abstract
Enterococcus faecalis is a Gram-positive lactic acid intestinal opportunistic bacterium with virulence potential. For a better understanding of the adapation of this bacterium to the host conditions, we performed a transcriptome analysis of bacteria isolated from an infection site (mouse peritonitis) by RNA-sequencing. We identified a total of 211 genes with significantly higher transcript levels and 157 repressed genes. Our in vivo gene expression database reflects well the infection process since genes encoding important virulence factors like cytolysin, gelatinase or aggregation substance as well as stress response proteins, are significantly induced. Genes encoding metabolic activities are the second most abundant in vivo induced genes demonstrating that the bacteria are metabolically active and adapt to the special nutrient conditions of the host. α- and β- glucosides seem to be important substrates for E. faecalis inside the host. Compared to laboratory conditions, the flux through the upper part of glycolysis seems to be reduced and more carbon may enter the pentose phosphate pathway. This may reflect the need of the bacteria under infection conditions to produce more reducing power for biosynthesis. Another important substrate is certainly glycerol since both pathways of glycerol catabolism are strongly induced. Strongly in vivo induced genes should be important for the infection process. This assumption has been verified in a virulence test using well characterized mutants affected in glycerol metabolism. This showed indeed that mutants unable to metabolize this sugar alcohol are affected in organ colonisation in a mouse model.
Highlights
Enterococci are Gram-positive bacteria that colonize several ecological niches, including the gut of mammals and numerous other animals
Enterococci are considered as “hard” bacteria due to their capacity to survive in harsh environments which are lethal for other bacteria [4,5] including the survival in a dessicated state on surfaces for months [6]
Identification of genes induced under infection conditions by RNA sequencing In order to identify genes induced during in vivo infection using RNA-Seq, RNA was prepared from E. faecalis V19 grown to mid-log phase or stationary phase in brain heart infusion (BHI) broth and from cells incubated 24 h in the mice peritoneum and sequenced on the Illumina GAIIx platform
Summary
Enterococci are Gram-positive bacteria that colonize several ecological niches, including the gut of mammals and numerous other animals. Major virulence factors of these candidates correspond to (i) extracellular matrix proteins like aggregation substance (AS), enterococcal surface protein (Esp), the E. faecalis antigene (EfaA), the adhesion to collagen (Ace), the endocarditis and biofilm associated pili (EbpA pili) and (ii) to cell and tissue damaging activities like the bacteriocin cytolysin (Cyl) and the protease gelatinase (GelE) [8]. Neither of these traits could be systematically identified in clinical isolates. We will present the first comprehensive in vivo expression database of a clinical isolate of E. faecalis obtained by RNA-seq
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