Microrheology and Spatial Heterogeneity of Staphylococcus aureus Biofilms Modulated by Hydrodynamic Shear and Biofilm-Degrading Enzymes

Abstract

Particle tracking microrheology was used to investigate the viscoelasticity of Staphylococcus aureus biofilms grown in microfluidic cells at various flow rates and when subjected to biofilm-degrading enzymes. Biofilm viscoelasticity was found to harden as a function of shear rate but soften with increasing height away from the attachment surface in good agreement with previous bulk results. Ripley's K-function was used to quantify the spatial distribution of the bacteria within the biofilm. For all conditions, biofilms would cluster as a function of height during growth. The effects of proteinase K and DNase-1 on the viscoelasticity of biofilms were also investigated. Proteinase K caused an order of magnitude change in the compliances, softening the biofilms. However, DNase-1 was found to have no significant effects over the first 6 h of development, indicating that DNA is less important in biofilm maintenance during the initial stages of growth. Our results demonstrate that during the preliminary stages of Staphylococcus aureus biofilm development, column-like structures with a vertical gradient of viscoelasticity are established and modulated by the hydrodynamic shear caused by fluid flow in the surrounding environment. An understanding of these mechanical properties will provide more accurate insights for removal strategies of early-stage biofilms.

Shear stress affects the architecture and cohesion of Chlorella vulgaris biofilms

“…In all cases, the flow was laminar (Reynolds number in the range 0.3 to 3.0). Shear stress (τ; in mPa) was calculated with the formula presented in Hart et al 26 as follow: where Q is the flow rate in mL/min, µ is the dynamic viscosity of water at 25 °C (0.89 mPa · s), w and h are the width and height of the flow cell channel respectively.…”

“…In order to test such hypothesis, the biofilms of Chlorella vulgaris were cultivated in flow-cells at several shear stress and their architecture characterized by confocal laser scanning microscopy (CLSM) and image analysis. Advanced microscopy techniques such as fluorescence recovery after photobleaching (FRAP) and particle tracking have been particularly useful in characterizing diffusion and the rheological properties of bacterial biofilms 25 , 26 and were therefore here employed together with an erosion test to determine the physical and cohesion properties of microalgae biofilms as a function of the shear stress.…”

Spatial Correlations and Distribution of Competence Gene Expression in Biofilms of Streptococcus mutans

“…In order to remove the quadratic behavior of K ( r ) that is characteristic of CSR, the function H ( r ) is often used ( Haase, 1995 ; Hart et al, 2019 ):…”

Biofilm and swarming emergent behaviours controlled through the aid of biophysical understanding and tools

“…External shear flows can also alter the mechanical properties of the biofilm. A study in S. aureus identified that an external shear stress of 1–10 mPa makes the biofilm three times harder than the one grown in static conditions, probably as a response to less favourable attachment conditions [ 92 , 93 ].…”