Biofilm formation of Staphylococcus aureus strains isolated from impetigo and furuncle: role of fibrinogen and fibrin.

The formation of membranous structure (thickness from the plastic tissue-culture coverslip (hematoxylin-eosin) > 1 mm; periodic acid-Schiff-positive) was more prominent with Staphylococcus aureus (S. aureus) strains isolated from impetigo (coagulase types I.V origin) than with S. aureus strains isolated from furuncle (coagulase type IV origin) (P < 0.05) in the plastic tissue-culture coverslip in human plasma after 72 h. Attachment of S. aureus cells to a plastic tissue-culture coverslip was more marked in 0-3% fibrinogen/tryptic soy broth (TSB) than in plasma (P < 0.05). The formation of the membranous structure was observed on the plastic tissue-culture coverslip with 0.3% fibrinogen/human serum but not with 0.3% fibrinogen + 5% glucose/TSB. Electron microscopy revealed abundant fibrin around S. aureus cells at 4 h and Ruthenium red-positive materials increased at 24 and 72 h in plasma. Staphylococcus aureus cell attachment to the plastic tissue-culture coverslip in plasma decreased by addition of levofloxacin (LVFX) at 1/2 minimum inhibitory concentration (MIC) and clarithromycin (CAM) at 1/4 MIC. Polysaccharide production of S. aureus cells on the plastic tissue-culture coverslip in plasma decreased with the addition of CAM at 1/4 MIC. Fibrinogen is closely related to initiation of infection but biofilm formation requires the conversion of fibrinogen to fibrin. Thus, attachment of S. aureus cells to the plastic tissue-culture coverslip, conversion of fibrinogen to fibrin by coagulase-prothrombin complex, and production of abundant glycocalyx by S. aureus cells are at least required for the production of biofilm in staphylococcal skin infection.