Objectives: Staphylococcus aureus (S. aureus) is a frequent cause of catheter-related infections (CRI). Coagulase activity, the hallmark of S. aureus, is the consequence of the activation of prothrombin to staphylothrombin by staphylocoagulase (coa) and von willebrand factor-binding protein (vWbp). Due to the direct activation of prothrombin, S. aureus staphylothrombin activity is insensitive to heparins or bivalent hirudin inhibitors, however, we have previously shown that the direct thrombin inhibitor dabigatran effectively blocks staphylothrombin. Our objective was to study the role of staphylothrombin and staphylothrombin-mediated fibrin in S. aureus CRI, as well as the potential of staphylothrombin inhibition by dabigatran as an adjunctive treatment.
Methods: We studied the effect of either pharmacological inhibition by dabigatran or genetic absence (coa-/vWbp-negative mutant) on fibrin adhesion and bacterial retention on catheter fragments in vitro as well as in a mouse model of jugular vein catheter infection.
Results: An early fibrin deposition was noted on fluorescence microscopy and SEM of catheter fragments inoculated with a Newman wild-type (Fig 1A), but not with the mutant strain (Fig 1B). Dabigatran, but not enoxaparin, prevented the formation of this fibrin sheat (Fig 1C). Staphylothrombin-mediated fibrin increased bacterial retention on catheter fragments in vitro a 1000-fold (6.04±0.55 log vs 3.00±0.23 log CFU/mL, p<0.001), and staphylothrombin inhibition significantly reduced the retention of S.aureus (4.20±0.42 log CFU/mL, p<0.001). Both genetic inactivation and chemical inhibition of staphylothrombin increased the susceptibility of catheter-grown S. aureus to vancomycin. In the mouse model, treatment with dabigatran reduced bacterial load on the catheter fragments (5.74 ±0.18 log vs 7.02±0.15CFU/mL, p<0.05; Fig 1D), as well as in the kidney (4.80±0.50 log vs 6.61±0.37 log CFU/mL, p<0.01; Fig 1E). The combination of staphylothrombin inhibition with vancomycin had an additional effect compared to either treatment alone (p<0.001 vs vancomycin alone and p<0.01 vs dabigatran alone) (Fig 1 D and E).
Conclusion: Staphylothrombin-mediated fibrin contributes to the retention of S. aureus on catheter fragments in vitro and in vivo, and to metastatic infectious complications. Furthermore, inhibition of staphylothrombin-driven fibrin deposition improved antibiotic susceptibility of S. aureus grown on catheter fragments in vitro and in vivo.