A novel in vitro model for haematogenous spreading ofS. aureusdevice biofilms demonstrating clumping dispersal as an advantageous dissemination mechanism

Abstract

Staphylococcus aureus is able to disseminate from vascular device biofilms to the blood and organs, resulting in life-threatening infections such as endocarditis. The mechanisms behind spreading are largely unknown, especially how the bacterium escapes immune effectors and antibiotics in the process. Using an in vitro catheter infection model, we studied S. aureus biofilm growth, late-stage dispersal, and reattachment to downstream endothelial cell layers. The ability of the released biofilm material to resist host response and disseminate in vivo was furthermore studied in whole blood and phagocyte survival assays and in a short-term murine infection model. We found that S. aureus biofilms formed in flow of human plasma release biofilm thromboemboli with embedded bacteria and bacteria-secreted polysaccharides. The emboli disseminate as antibiotic and immune resistant vehicles that hold the ability to adhere to and initiate colonisation of endothelial cell layers under flow. In vivo experiments showed that the released biofilm material reached the heart similarly as ordinary broth-grown bacteria but also that clumps to some extend were trapped in the lungs. The clumping dispersal of S. aureus from in vivo-like vascular biofilms and their specific properties demonstrated here help explain the pathophysiology associated with S. aureus bloodstream infections.

Distinct phenotypic traits of Staphylococcus aureus are associated with persistent, contagious bovine intramammary infections

“…These results support previous studies, showing a high prevalence of genes of the icaA and icaD loci among S. aureus mastitis isolates 32 , 33 . As reported for the clumping dispersal in S. aureus bloodstream infections 34 , high levels of PNAG in biofilm could be an advantageous dissemination mechanism by facilitating staphylococcal bacteria-to-bacteria interaction, which mediates the dispersal ability of the pathogen in the bovine mammary gland.…”

The staphylococcal exopolysaccharide PIA – Biosynthesis and role in biofilm formation, colonization, and infection

“…Before the discovery of PIA, some studies reported an impact of slime production on the pathogenesis of S. epidermidis device-related infection [147] and an association with origin from infection, for example from nosocomial bacteremia [148] , while others did not [148] , [149] . In addition to the assumption that clumping/slime production increases the success of infections on indwelling medical devices, recent research also has suggested that this phenotype increases the chances of staphylococcal dissemination through the bloodstream [150] .…”

A Method for Quantification of Epithelium Colonization Capacity by Pathogenic Bacteria

“…Of note, we have obtained preliminary results showing that the method can be conducted with live endothelial cells using diluted human plasma as only source of nutrients. This provides an even more physiological correct medium that both supports S. aureus growth and endothelial viability and further contains fibrinogen and coagulation components which are used by S. aureus to form thrombotic biofilms (Grønnemose et al, 2017 ).…”

“…However, this requires termination of a rather laborious experiment, leaving only a single data point measured per chamber. Furthermore, CFU enumeration of bacteria exposed to in vivo -like stress conditions can be tricky, since bacteria may change morphology, i.e., become filamentous (Klein et al, 2015 ; Khandige et al, 2016 ), or aggregate (Loof et al, 2015 ; Grønnemose et al, 2017 ; Sønderholm et al, 2017 ), or slow down growth speed (Proctor et al, 2006 ), which may affect the accuracy of bacterial quantification by traditional plating techniques.…”