Abstract
Bacterial infection and thrombosis are highly correlated, especially in patients with indwelling medical devices. Coagulase-negative staphylococci, typified by Staphylococcus epidermidis, are a common cause of medical device infections owing to their biofilm forming capacity which provides protection from antibiotics and host immune response. Attention has been drawn to the interaction between S. epidermidis and host proteins, specifically fibrinogen. However, little is known regarding the impact of the transition from planktonic to biofilm forming phenotype on this interaction. Here we investigate the growth phase dependence of bacteria-fibrinogen interaction and the resulting effect on fibrin clot formation, structure, and mechanics. Flow cytometry demonstrated growth phase dependent affinity for fibrinogen. To mimic intravascular device seeding, we quantified the adhesion of S. epidermidis to a fibrinogen coated surface under continuous flow conditions in vitro. The bacterial deposition rate onto fibrinogen was significantly greater for stationary (5,360 ± 1,776 cells/cm2s) versus exponential phase (2,212 ± 264, cells/cm2 s). Furthermore, the expression of sdrG–a cell surface adhesion protein with specificity for fibrinogen–was upregulated ∼twofold in the stationary versus the exponential phase. Rheometry and confocal microscopy demonstrated that stationary phase S. epidermidis slows clot formation and generates a more heterogeneous fibrin network structure with greater elasticity (G′ = 5.7 ± 1.0 Pa) compared to sterile fibrinogen (G′ = l.5 ± 0.2 Pa), while exponential phase cells had little effect. This work contributes to the current understanding of the growth phase dependent regulation of bacterial virulence factors and the correlation between bacterial infection and thrombosis.
Highlights
Pathologic clots, for example, venous thromboembolism and embolic cerebrovascular accidents, are highly correlated with bacterial infection (Raad et al, 1994; Grau et al, 1995; Samama, 2000; Dalager-Pedersen et al, 2014)
To determine if the increased affinity translated to actual adhesion to a fibrinogen coated surface, where shear induced binding enhancement may contribute, we evaluated deposition rate and residence time in a continuous flow, parallelplate system
Labeled S. epidermidis flowing past immobilized fibrinogen appear as streaks on image capture but are more clearly defined circular shapes as they slow and come to rest on the surface (Figures 2A–E)
Summary
Pathologic clots, for example, venous thromboembolism and embolic cerebrovascular accidents, are highly correlated with bacterial infection (Raad et al, 1994; Grau et al, 1995; Samama, 2000; Dalager-Pedersen et al, 2014). SdrG binding to fibrinogen is strengthened under conditions of shear stress (e.g., fluid flow like that seen around vascular catheters) (Weaver et al, 2011; Milles et al, 2018) and is extremely strong, approaching that of a covalent bond (Herman et al, 2014) It appears that SdrG binding is sensitive to forces generated under typical centrifugation conditions and highly strain dependent (Vanzieleghem et al, 2015). Despite this potential complexity in binding activity, antibodies against this CWA surface protein block S. epidermidis interactions with peripheral venous catheters (Pei and Flock, 2001) and diminished CVC associated infection and resulting bacteremia in mice (Guo et al, 2007). SdrG is considered a critical mediator of the interaction between S. epidermidis infection and thrombosis
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