title: An extracellular Staphylococcus epidermidis polysaccharide: relation to Polysaccharide Intercellular Adhesin and its implication in phagocytosis.
abstract: BACKGROUND
  The skin commensal and opportunistic pathogen Staphylococcus epidermidis is a leading cause of hospital-acquired and biomaterial-associated infections. The polysaccharide intercellular adhesin (PIA), a homoglycan composed of β-1,6-linked N-acetylglucosamine residues, synthesized by enzymes encoded in icaADBC is a major functional factor in biofilm accumulation, promoting virulence in experimental biomaterial-associated S. epidermidis infection. Extracellular mucous layer extracts of S. epidermidis contain another major polysaccharide, referred to as 20-kDa polysaccharide (20-kDaPS), composed mainly out of glucose, N-acetylglucosamine, and being partially sulfated. 20-kDaPS antiserum prevents adhesion of S. epidermidis on endothelial cells and development of experimental keratitis in rabbits. Here we provide experimental evidence that 20-kDaPS and PIA represent distinct molecules and that 20-kDaPS is implicated in endocytosis of S. epidermidis bacterial cells by human monocyte-derived macrophages.
  
  
  RESULTS
  Analysis of 75 clinical coagulase-negative staphylococci from blood-cultures and central venous catheter tips indicated that 20-kDaPS is expressed exclusively in S. epidermidis but not in other coagulase-negative staphylococcal species. Tn917-insertion in various locations in icaADBC in mutants M10, M22, M23, and M24 of S. epidermidis 1457 are abolished for PIA synthesis, while 20-kDaPS expression appears unaltered as compared to wild-type strains using specific anti-PIA and anti-20-kDaPS antisera. While periodate oxidation and dispersin B treatments abolish immuno-reactivity and intercellular adhesive properties of PIA, no abrogative activity is exerted towards 20-kDaPS immunochemical reactivity following these treatments. PIA polysaccharide I-containing fractions eluting from Q-Sepharose were devoid of detectable 20-kDaPS using specific ELISA. Preincubation of non-20-kDaPS-producing clinical strain with increasing amounts of 20-kDaPS inhibits endocytosis by human macrophages, whereas, preincubation of 20-kDaPS-producing strain ATCC35983 with 20-kDaPS antiserum enhances bacterial endocytosis by human macrophages.
  
  
  CONCLUSIONS
  In conclusion, icaADBC is not involved in 20-kDaPS synthesis, while the chemical and chromatographic properties of PIA and 20-kDaPS are distinct. 20-kDaPS exhibits anti-phagocytic properties, whereas, 20-kDaPS antiserum may have a beneficial effect on combating infection by 20-kDaPS-producing S. epidermidis.
authors.affiliation: Department of Microbiology, School of Medicine, University of Patras, Patras, Greece.
authors.forename: Anastasia I
authors.initials: AI
authors.lastname: Spiliopoulou
authors.forename: Maria I
authors.initials: MI
authors.lastname: Krevvata
authors.forename: Fevronia
authors.initials: F
authors.lastname: Kolonitsiou
authors.forename: Llinos G
authors.initials: LG
authors.lastname: Harris
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Wilkinson
authors.forename: Angharad P
authors.initials: AP
authors.lastname: Davies
authors.forename: Georgios O
authors.initials: GO
authors.lastname: Dimitracopoulos
authors.forename: Nikos K
authors.initials: NK
authors.lastname: Karamanos
authors.forename: Dietrich
authors.initials: D
authors.lastname: Mack
authors.forename: Evangelos D
authors.initials: ED
authors.lastname: Anastassiou
mesh_terms: D002478:Cells, Cultured; D004251:DNA Transposable Elements; D020869:Gene Expression Profiling; D006801:Humans; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology*; D008970:Molecular Weight; D016254:Mutagenesis, Insertional; D010587:Phagocytosis; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D013212:Staphylococcus epidermidis / Q000276:immunology* / Q000378:metabolism*
chemical_list: D004251:DNA Transposable Elements; D011135:Polysaccharides, Bacterial; C113579:polysaccharide intercellular adhesin