Biofilm formation induces C3a release and protects Staphylococcus epidermidis from IgG and complement deposition and from neutrophil-dependent killing.
BACKGROUND
Biofilm formation is considered to be an important virulence factor of the opportunistic pathogen Staphylococcus epidermidis. We hypothesized that biofilm formation could interfere with the deposition of immunoglobulins and complement on the bacterial surface, leading to diminished activation of the complement system and protection from killing by human phagocytes.


METHODS
The killing of biofilm-encased and planktonically grown wild-type (wt) S. epidermidis and the killing of an isogenic biofilm-negative ica mutant (ica(-)) by human polymorphonuclear neutrophils (PMNs) were compared. C3a induction and deposition of C3b and immunoglobulin G (IgG) on the bacteria after opsonization with human serum were assessed by enzyme-linked immunosorbent assay, flow cytometry, and electron microscopy. The virulence of the bacterial strains was compared in a mouse model of catheter-associated infection.


RESULTS
Biofilm-embedded wt S. epidermidis was killed less well by human PMNs and induced more C3a than planktonically grown wt and ica(-) S. epidermidis. However, the deposition of C3b and IgG on the bacterial surface was diminished in biofilm-encased staphylococci. wt S. epidermidis was more virulent in implant-associated infections and was killed more slowly than ica(-) in ex vivo assays of killing by PMNs.


CONCLUSIONS
The results indicate that prevention of C3b and IgG deposition on the bacterial surface contributes to the biofilm-mediated protection of S. epidermidis from killing by PMNs.
Kristian
Sascha A
SA
Division of Infectious Diseases, Department of Research, University Hospitals Basel, Basel, Switzerland.
Birkenstock
Timo A
TA
Sauder
Ursula
U
Mack
Dietrich
D
Götz
Friedrich
F
Landmann
Regine
R
D000818:Animals; D018441:Biofilms / Q000254:growth & development*; D002408:Catheters, Indwelling / Q000382:microbiology; D015169:Colony Count, Microbial; D003176:Complement C3 / Q000276:immunology* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D050296:Microbial Viability; D008854:Microscopy, Electron; D009504:Neutrophils / Q000276:immunology*; D009895:Opsonin Proteins / Q000378:metabolism; D013203:Staphylococcal Infections / Q000382:microbiology; D013212:Staphylococcus epidermidis / Q000276:immunology* / Q000472:pathogenicity*
D003176:Complement C3; D007074:Immunoglobulin G; D009895:Opsonin Proteins