Speckle fluctuations reveal dynamics of microparticles in fibrin scaffolds in a model of bacterial infection

Fibrin plays an important role in both immune response and pathogen virulence during bacterial infection. Pathogens such as staphylococci interact with fibrin through dynamic processes, involving binding, entrapment, and release from fibrin scaffolds, through which they experience an evolving cascade of nano- to microscale dynamics that span broad timescales. Yet, the biophysical dynamics that unfold between invading bacteria and host fibrin are not well understood. Here, we present a non-invasive optical approach based on speckle fluctuation to characterize the multiscale dynamics of microparticles in fibrin scaffolds. Using microparticles of varying sizes and surface chemistry to emulate spherical, non-motile bacterial cells, we demonstrate real-time monitoring of bacteria-fibrin interactions during fibrin clot formation and fibrinolysis in purified fibrins scaffolds and clinical plasma clots. Our approach circumvents the need for sophisticated position tracking equipment, making it potentially applicable to a broad range of experimental systems for biophysical investigation of bacteria-extracellular network interactions.