Bacterial factors required for biofilm formation in Staphylococcus epidermidis are linked to contact activation

Staphylococcus epidermidis is a leading cause of device-associated bloodstream infections, where biofilm formation contributes to persistence in direct contact with host plasma. While extracellular matrix components are central to biofilm development, their functional consequences at the host-pathogen interface remain incompletely understood. Here, we investigated whether bacterial factors required for biofilm formation are associated with activation of the intrinsic coagulation pathway in human plasma. Clinical isolates of S. epidermidis that accelerated clotting time in plasma also showed stronger biofilm formation. S. epidermidis mutants, deficient in polysaccharide intercellular adhesin (PIA) or the autolysin AtlE were impaired in biofilm formation and had prolonged clotting times compared to their wild type. The wild-type strain induced activation of factor XII and plasma kallikrein, accelerated intrinsic coagulation, and degraded high-molecular-weight kininogen, effects absent in the AtlE and PIA mutants. Notably, DNase I treatment of the wild-type strain prolonged intrinsic coagulation time and prevented high-molecular-weight kininogen degradation, identifying bacterial extracellular DNA as a possible central driver of contact activation. The D5-derived peptide HKH20, previously shown to inhibit contact activation, also reduced S. epidermidis-induced activation of contact factors. In plasma, HKH20 decreased the formation and size of bacterial aggregates and altered biofilm architecture by modulating fibrin network formation. Together, these findings identify extracellular DNA and PIA as biofilm-relevant bacterial factors that are linked to contact system activation and intrinsic coagulation in plasma, highlighting an unexpected functional interface between biofilm matrix components and host plasma defense mechanisms.