Lysozyme facilitates adherence of Enterococcus faecium to host cells and induction of necrotic cell death

A virulence factor as a therapeutic: the probiotic Enterococcus faecium SF68 arginine deiminase inhibits innate immune signaling pathways

The probiotic bacterial strain Enterococcus faecium SF68 has been shown to alleviate symptoms of intestinal inflammation in human clinical trials and animal feed supplementation studies. To identify factors involved in immunomodulatory effects on host cells, E. faecium SF68 and other commensal and clinical Enterococcus isolates were screened using intestinal epithelial cell lines harboring reporter fusions for NF-κB and JNK(AP-1) activation to determine the responses of host cell innate immune signaling pathways when challenged with bacterial protein and cell components. Cell-free, whole-cell lysates of E. faecium SF68 showed a reversible, inhibitory effect on both NF-κB and JNK(AP-1) signaling pathway activation in intestinal epithelial cells and abrogated the response to bacterial and other Toll-like receptor (TLR) ligands. The inhibitory effect was species-specific, and was not observed for E. avium, E. gallinarum, or E. casseliflavus. Screening of protein fractions of E. faecium SF68 lysates yielded an active fraction containing a prominent protein identified as arginine deiminase (ADI). The E. faecium SF68 arcA gene encoding arginine deiminase was cloned and introduced into E. avium where it conferred the same NF-_κB inhibitory effects on intestinal epithelial cells as seen for E. faecium SF68. Our results indicate that the arginine deiminase of E. faecium SF68 is responsible for inhibition of host cell NF-κB and JNK(AP-1) pathway activation, and is likely to be responsible for the anti-inflammatory and immunomodulatory effects observed in prior clinical human and animal trials. The implications for the use of this probiotic strain for preventive and therapeutic purposes are discussed.

Enhanced expressions of lysozyme, SLPI and glycoprotein 340 in biofilm-associated chronic rhinosinusitis

Lysozyme, secretory leukocyte proteinase inhibitor (SLPI) and glycoprotein 340 (gp340) are important effectors of the innate immune system in sinonasal mucosa. Bacterial biofilms (BBF) are highly organized bacterial communities resistant to host defense systems. The aim of this study was to investigate the expression of lysozyme, SLPI and gp340 in sinus mucosa from chronic rhinosinusitis (CRS) patients with different BBF status. In this prospective cohort study, 63 CRS patients undergoing endoscopic sinus surgery and 20 controls were enrolled and their mucosal samples from ethmoid sinus were obtained. Biofilms were examined by confocal scanning laser microscopy (CSLM), and the expressions of lysozyme, SLPI and gp340 in mRNA and protein levels were detected using reverse transcription polymerase chain reaction (RT-PCR), immunohistochemistry and Western blot assay, respectively. As a result, 35/63 (55.6%) of the patients were BBF positive in the CRS group and none in controls. Both mRNA and protein levels of lysozyme, SLPI and gp340 in patients with CRS were significantly higher than those in controls. When sub-classified according to BBF status, the CRS patients with BBF revealed the significantly enhanced mRNA and protein levels of lysozyme, SLPI and gp340. In conclusion, our study demonstrates that lysozyme, SLPI and gp340 are constitutively expressed in sinus mucosa and their up-regulated expressions on both the mRNA and protein levels are associated with BBF in CRS patients. These findings may offer an insight into the interaction between BBF and the innate immune system.

The cell wall architecture of Enterococcus faecium: from resistance to pathogenesis

The cell wall of Gram-positive bacteria functions as a surface organelle that continuously interacts with its environment through a plethora of cell wall-associated molecules. Enterococcus faecium is a normal inhabitant of the GI tract of mammals, but has recently become an important etiological agent of hospital-acquired infections in debilitated patients. Insights into the assembly and function of enterococcal cell wall components and their interactions with the host during colonization and infection are essential to explain the worldwide emergence of E. faecium as an important multiantibiotic-resistant nosocomial pathogen. Understanding the biochemistry of cell wall biogenesis and principles of antibiotic resistance at the molecular level may open up new frontiers in research on enterococci, particularly for the development of novel antimicrobial strategies. In this article, we outline the current knowledge on the most important antimicrobial resistance mechanisms that involve peptidoglycan synthesis and the role of cell wall constituents, including lipoteichoic acid, wall teichoic acid, capsular polysaccharides, LPxTG cell wall-anchored surface proteins, WxL-type surface proteins and pili, in the pathogenesis of E. faecium.

Enterococcus faecalis internalization in human umbilical vein endothelial cells (HUVEC)

Initial Enterococcus faecalis-endothelial cell molecular interactions which lead to enterococci associating in the host endothelial tissue, colonizing it and proliferating there can be assessed using in vitro models. Cultured human umbilical vein endothelial cells (HUVEC) have been used to study other Gram-positive bacteria-cell interactions; however, few studies have been aimed at establishing the relationship of E. faecalis with endothelial cells. The aggregation substance (AS) family of adhesins represents an E. faecalis virulence factor which has been implicated in endocarditis severity and bacterial persistence. The Asc10 protein (a member of this family) promotes bacterium-bacterium aggregation and bacterium-host cell binding. Evaluating Asc10 role in bacterial internalization by cultured enterocytes has shown that this adhesin facilitates E. faecalis endocytosis by HT-29 cells. A few eukaryotic cell structural components, such as cytoskeletal proteins, have been involved in E. faecalis entry into cell-lines; it is thus relevant to determine whether Asc10, as well as microtubules and actin microfilaments, play a role in E. faecalis internalization by cultured endothelial cells. The role of Asc10 and cytoskeleton proteins in E. faecalis ability to enter HUVEC was assessed in the present study, as well as cell apoptosis induction by enterococcal internalization by HUVEC; the data indicated increased cell apoptosis and that cytoskeleton components were partially involved in E. faecalis entry to endothelial cells, thereby suggesting that E. faecalis Asc10 protein would not be a critical factor for bacterial entry to cultured HUVEC.