Viscoelasticity of Staphylococcus aureus Biofilms in Response to Fluid Shear Allows Resistance to Detachment and Facilitates Rolling Migration

Abstract

Staphylococcus aureus is a leading cause of catheter-related bloodstream infections and endocarditis. Both involve (i) biofilm formation, (ii) exposure to fluid shear, and (iii) high rates of dissemination. We found that viscoelasticity allowed S. aureus biofilms to resist detachment due to increased fluid shear by deformation, while remaining attached to a surface. Further, we report that S. aureus microcolonies moved downstream by rolling along the lumen walls of a glass flow cell, driven by the flow of the overlying fluid. The rolling appeared to be controlled by viscoelastic tethers. This tethered rolling may be important for the surface colonization of medical devices by nonmotile bacteria.Biofilm infections are increasingly associated with a variety of medical prostheses (e.g., vascular and orthopedic implants) and delivery devices (e.g., percutaneous catheters), as well as with diseases such as native-valve endocarditis and infectious kidney stones (1,2,3,13). Staphylococcus aureus is a key pathogen, feared for its high mortality rate and antibiotic resistance (10). Endovascular biofilm infections caused by S. aureus also carry a high risk of metastasis (4, 10). These biofilms are exposed to a broad range of fluid shears, ranging from the continuous, laminar flow in infected infusion lines to the highly variable, turbulent flow in the case of bacterial vegetations on a heart valve. Therefore, the continuous adaptation to mechanical stresses is an important feature of biofilm physiology (7). The responses of biofilms to shear stresses may determine biofilm dissemination in general and the rate of formation and size of biofilm emboli in particular. In previous work, we showed that S. aureus biofilm emboli ranged in size from single cells to microcolonies containing thousands of cells in an in vitro catheter infection model (6). Large emboli expressed antibiotic (oxacillin) tolerance similar to that observed in attached biofilms. In the present study, we used a glass capillary system previously used to mimic physiological shear in both catheter (6) and vascular (9) infection models to quantify the viscoelastic response and motion of S. aureus biofilm microcolonies in response to varying or steady fluid shear over short (seconds) and sustained (minutes) periods. Biofilms were grown from an S. aureus strain (ATTC 25923) on 1/10-strength brain heart infusion broth at 37°C. One milliliter of a 24-h broth culture was inoculated into a 1-mm 2 , 140-mm-long glass capillary flow cell (model FC91; BioSurface Technologies, Bozeman, Mont.) integrated into a once-through flow system. Biofilms were monitored with a Cohu (San Diego, Calif.) model 4910 camera mounted on an Olympus BH2 microscope using Scion Image software (Scion Inc., Frederick, Md.). After an attachment period of 30 min, a continuous laminar flow rate (Q) of 60 ml h Ϫ1 was established to approximate the hydrodynamic conditions typically used in a central venous catheter (6). The average velocity was 1.67 cm s Ϫ1 , the Reynolds number was 17, and the wall ...

Kinneyia: A Flow-Induced Anisotropic Fossil Pattern from Ancient Microbial Mats

“…In fact, modern biofilms and microbial mats are found to behave like viscoelastic films (Shaw et al, 2004;Vinogradov et al, 2004;Rupp et al, 2005;Lieleg et al, 2011). Lieleg et al (2011) have shown that biofilms display elastic-like responses for high frequency stimuli, and viscous-fluid responses when low frequency mechanical stimuli are applied.…”

Living bacteria rheology: Population growth, aggregation patterns, and collective behavior under different shear flows

“…Particular focus has been given to the viscoelasticity of cell attachment and detachment, under the influence of antibiotics and flows with different shear rates [14][15][16]. In these studies, the analysis of cells detachment was performed only in small time slots, at specific biofilm growth stages.…”

Biomechanical Analysis of Infectious Biofilms

“…1, the relationship between the deformation and growth of immersed biofilms and the shear stresses generated by the surrounding fluid flow is complex and bidirectional. Biofilm morphology influences local flow patterns and hence the fluxes of dispersed phases such as nutrients, metabolites, and quorum sensing molecules [86,87,101], and flow can drive biofilm morphogenesis to rippled beds [42,89], streamers [80,89,90,101], and rolling clusters [79]. The relevance of such process to the formation, growth, and dispersal of both infectious and non-infectious biofilms demands quantitative modelling with a predictive capability, but this situation is far from being realised.…”