Investigating the Role of Mechanical Forces in the Catheter-Related Pathogenesis of Staphylococci, From Adhesion to Biofilm Formation

Intravenous catheter related blood stream infections (CRBSI) are the major cause of healthcare-associated infections to date, and result in both increased morbidity and mortality in patients with undeveloped and compromised immunity, as well as a significant cost burden on health systems. Staphylococcus epidermidis and S. aureus are both normal inhabitants of human skin and mucous membranes and also are the organisms most significantly cultured from these infections. CRBSIs from Staphylococci can be extremely harmful if left untreated even for a mater of a few days. These infections can result in serious conditions such as native valve endocarditis, and even bacteremia sepsis.The pathogenesis is complex, involving multicellular choreography and host immune evasion, however it is well accepted that two key steps are (i) adhesion to the catheter lumen by planktonic cells and (ii) subsequent biofilm formation to establish a stable source of bacterial cells for infection. Adhesion is largely mediated by surface exposed adhesins, targeting a number of soluble host plasma proteins and extracellular matrix components. Biofilm formation has been shown to occur through a number of pathways, however a commonly occurring theme is through secretion of polysaccharide intracellular adhesin (PIA) matrix, driven by expression of the chromosomal icaADBC operon.We have developed a novel toolset using microfluidics to recapitulate the pathogenic environment incorporating clinically relevant fluid shear stress. Using this microfluidic assay, we show that shear stress from fluid flow modulated the pathogenic potential of S. epidermidis, both in terms of increased adhesive capability as well as the induction of biofilm formation is normally quiescent strains. Further, we have developed a high-throughput, multidimensional microfluidic assay incorporating functional adhesive protein microarrays and large scale microfluidic networks. This assay will be used to generate quantitative `pathogenicity landscapes' in Staphylococci, towards the identification of novel therapeutic targets to mitigate and treat device related infections