PB1377 - Studying the Activation of Blood Coagulation Induced by Staphylococcal Biofilms: Unraveling the Link Between Infections and Thrombosis

Background: Infective endocarditis (IE) is an infection of the cardiac endothelium. It has an annual incidence of 3–10/100,000 of the population with a mortality of up to 30%[10.1086/592576]. Staphylococcus aureus is the most prevalent cause of IE, accounting for approximately 27% of all cases[10.1093/cid/cis199]. After endothelial injury, bacterial colonisation is facilitated, thus triggering additional endothelial injury and thrombus formation. Production of a biofilm (multicellular community of microorganisms, enclosed in a self-produced extracellular matrix) assists bacterial persistence and contributes to antibiotic tolerance[10.1016/S0140-6736(15)00067].

Aims: Considered that thrombotic complications are often associated with IE, here we explore the possibility that biofilms produced by Staphylococcus aureus (coagulase +) and Staphylococcus epidermidis (coagulase -), could induce fibrin generation in human plasma and investigate their ability to convert directly fibrinogen into insoluble fibrin in vitro.

Methods: S. aureus and S. epidermidis were cultured each at 37°C in LB broth, added to a 96-well microtiter plate and incubated at 37°C for 36h, leading to the formation of bacterial biofilms. To test fibrin generation in plasma, diluted(1:2) human plasma was added to each biofilm and to empty wells as a blank experiment. To test fibrin generation from purified fibrinogen, a solution of fibrinogen(0.15 mg/mL) was added to each biofilm and to empty wells as a control. In both assays, fibrin generation was monitored by turbidimetry.

Results: The data obtained indicate that: both biofilms of S. aureus and S. epidermidis efficiently and similarly induce fibrin clotting in human plasma; both biofilms of S. aureus and S. epidermidis do not convert isolated fibrinogen solutions into fibrin.

Conclusion(s): The results of this study point out that bacterial biofilms can trigger blood coagulation, thus providing the molecular basis for explaining the positive relationship between IE, biofilm formation and an increased thrombotic risk. Further studies are needed to elucidate the biochemical mechanisms underlying biofilm-induced activation of blood coagulation.