Ultrastructural organization and regulation of a biomaterial adhesin of Staphylococcus epidermidis

Abstract

Coagulase-negative staphylococci have emerged as important pathogens in infections associated with intravascular devices. Microbial adherence to biomaterial surfaces is a crucial step in the pathogenesis of these infections. Staphylococcal surface proteins (herein referred to as SSP-1 and SSP-2) are involved in the attachment of Staphylococcus epidermidis 354 to polystyrene. In the present study we show that the adhesin protrudes from the cell surface as a fimbria-like polymer. Furthermore, in vitro proteolytic cleavage of SSP-1 produces an SSP-2-like protein which coincides with a loss of adhesive function. SSP-1 expression is downregulated in a phenotypical variant of S. epidermidis 354 whereas SSP-2 expression is not. These results could suggest that proteolytic cleavage is a key to the regulation of the adhesive state of S. epidermidis in vivo.Over the last 2 decades coagulase-negative staphylococci (CoNS), particularly strains of Staphylococcus epidermidis, have emerged as important pathogens in association with foreign bodies, e.g., intravascular devices. Especially in immunocompromised patients, such as cancer patients and premature neonates, catheter-related sepsis due to CoNS may be a lifethreatening complication (1, 2, 5, 12, 13). For many microorganisms, adhesion to host surfaces is a crucial step in the pathogenic process and a prerequisite for colonization of these surfaces (3). It has been demonstrated that CoNS adhere avidly to a variety of biomaterials such as Teflon and polystyrene (6,8,16,19). The initial phase of attachment was found to be correlated with surface hydrophobicity. Both hydrophobicity and adherence were reduced by proteases, such as pepsin, suggesting that hydrophobic cell surface proteins may play an important role in the initial attachment to biomaterials (8,16). In a previous study (19), we identified a proteinaceous antigen of S. epidermidis 354 that apparently is involved in adherence to polystyrene. Evidence was obtained that this antigen, herein referred to as staphylococcal surface proteins (SSP-1 and SSP-2), is present on fimbria-like appendages protruding from the bacterial cell surface. A monoclonal antibody specific for SSP-1 and SSP-2 was shown to be specific and as effective as proteases in preventing this staphylococcal strain from adhering to polystyrene (19). This strain thus provides a model system to study the adherence of CoNS to intravascular devices. In the present study we present data concerning the ultrastructural organization of the staphylococcal fimbria-like appendages, the structural and functional relationship between the antigenically related SSP-1 and SSP-2 proteins, and aspects of adhesion regulation in vivo. For cryo-ultramicrotomy and immunogold-labeling purposes, staphylococci, grown on blood agar plates, were inoculated in nutrient broth (Difco) and cultured overnight at 37ЊC. After being washed with phosphate-buffered saline (PBS), the bacteria were resuspended and fixed for 1 h in PBS containing 2% paraformaldehyde and 0.25% glutaraldehyde. ...

Staphylococcal Biofilms

“…Aap may be identical to the SSP-1 and SSP-2 proteins, which have been implicated in biofilm formation but whose identity was not investigated further (Veenstra et al 1996). Interestingly, it was shown that SSP forms protein strands on the S. epidermidis surface, thus possibly contributing to cell-cell adhesion over greater distances.…”

Biofilm characteristics of Staphylococcus epidermidis isolates associated with device-related meningitis

“…Isolates were deemed to be strongly biofilm-positive when the biofilm A 492 was .0.24 (indicated by the dotted line). surface proteins SSP-1 and SSP-2 have been implicated as being important factors for efficient primary attachment at the initial stages of the process (Veenstra et al, 1996). Further investigations into the role of S. epidermidis cellsurface adhesins, as well as examining the global regulatory systems that control their expression, are likely to lend more insight into the contribution that protein factors have to the biofilm-forming process.…”

Genetic and phenotypic analysis of biofilm phenotypic variation in multiple Staphylococcus epidermidis isolates

“…Adherence of S. epidermidis to prosthetic devices is thought to occur in two distinct steps: (i) initial attachment to the biomaterial surface, and (ii) subsequent accumulation of bacterial cells involving intercellular adhesion. Factors involved in the initial attachment to the polymer surface include non-specific interactions as well as specific adhesins including SSP-1 (Veenstra et al, 1996), SSP-2 (Veenstra et al, 1996) and AtlE (Heilmann et al, 1997). In addition, the biomaterial rapidly becomes coated with cellular matrix proteins such as fibronectin, fibrinogen and vitronectin.…”