Exploring the role of E. faecalis enterococcal polysaccharide antigen (EPA) and lipoproteins in evasion of phagocytosis

• Published in: Molecular microbiology Vol. 122; no. 2; pp. 230 - 242
• Main Authors: Norwood, Joshua S., Davis, Jessica L., Salamaga, Bartłomiej, Moss, Charlotte E., Johnston, Simon A., Elks, Philip M., Kiss‐Toth, Endre, Mesnage, Stéphane
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.08.2024
• Subjects: Animals; Antigens; Antigens, Bacterial - genetics; Antigens, Bacterial - immunology; Antigens, Bacterial - metabolism; Biological activity; Cell surface; Cell walls; Clonal deletion; Decoration; Enterococcus faecalis; Enterococcus faecalis - genetics; Enterococcus faecalis - immunology; Enterococcus faecalis - metabolism; EPA; Gene deletion; Humans; Immune Evasion; Immunity, Innate; innate immune evasion; Lipoproteins; Lipoproteins - genetics; Lipoproteins - metabolism; Macrophages; Macrophages - immunology; Macrophages - metabolism; Macrophages - microbiology; Mice; Nosocomial infection; Opportunist infection; Phagocytosis; Polymers; Polysaccharides; Polysaccharides, Bacterial - immunology; Polysaccharides, Bacterial - metabolism; Saccharides; Structure-function relationships; Virulence; Enterococcus faecalis; phagocytosis; innate immune evasion; lipoproteins; EPA
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.15294

Enterococcus faecalis is an opportunistic pathogen frequently causing nosocomial infections. The virulence of this organism is underpinned by its capacity to evade phagocytosis, allowing dissemination in the host. Immune evasion requires a surface polysaccharide produced by all enterococci, known as the enterococcal polysaccharide antigen (EPA). EPA consists of a cell wall‐anchored rhamnose backbone substituted by strain‐specific polysaccharides called ‘decorations’, essential for the biological activity of this polymer. However, the structural determinants required for innate immune evasion remain unknown, partly due to a lack of suitable validated assays. Here, we describe a quantitative, in vitro assay to investigate how EPA decorations alter phagocytosis. Using the E. faecalis model strain OG1RF, we demonstrate that a mutant with a deletion of the locus encoding EPA decorations can be used as a platform strain to express heterologous decorations, thereby providing an experimental system to investigate the inhibition of phagocytosis by strain‐specific decorations. We show that the aggregation of cells lacking decorations is increasing phagocytosis and that this process does not involve the recognition of lipoproteins by macrophages. Collectively, our work provides novel insights into innate immune evasion by enterococci and paves the way for further studies to explore the structure/function relationship of EPA decorations. Enterococci produce a cell surface polysaccharide called the enterococcal polysaccharide antigen (EPA) that protects these bacteria from being recognised and destroyed by immune cells. We describe an in vitro assay to explore the structure/function relationships of EPA and to identify cell surface components recognised by the immune system.