Streptococcus mutans biofilm transient viscoelastic fluid behaviour during high-velocity microsprays

Abstract

Using high-speed imaging we assessed Streptococcus mutans biofilm-fluid interactions during exposure to a 60-ms microspray burst with a maximum exit velocity of 51m/s. S. mutans UA159 biofilms were grown for 72h on 10mm-length glass slides pre-conditioned with porcine gastric mucin. Biofilm stiffness was measured by performing uniaxial-compression tests. We developed an in-vitro interproximal model which allowed the parallel insertion of two biofilm-colonized slides separated by a distance of 1mm and enabled high-speed imaging of the removal process at the surface. S. mutans biofilms were exposed to either a water microspray or an air-only microburst. High-speed videos provided further insight into the mechanical behaviour of biofilms as complex liquids and into high-shear fluid-biofilm interaction. We documented biofilms extremely transient fluid behaviour when exposed to the high-velocity microsprays. The presence of time-dependent recoil and residual deformation confirmed the pivotal role of viscoelasticity in biofilm removal. The air-only microburst was effective enough to remove some of the biofilm but created a smaller clearance zone underlying the importance of water and the air-water interface of drops moving over the solid surface in the removal process. Confocal and COMSTAT analysis showed the high-velocity water microspray caused up to a 99.9% reduction in biofilm thickness, biomass and area coverage, within the impact area.

Fluid‐driven interfacial instabilities and turbulence in bacterial biofilms

“…Recently, we had developed a microfluidic flow channel system for investigating rapid high velocity water and air microspray interactions with S. mutans biofilms for dental cleaning applications (Fabbri et al, 2015). HSC videography suggested the formation of migratory ripple-like structures at the biofilm/fluid interface.…”

“…S. mutans biofilms have been widely used in research to investigate biofilm mechanical properties and detachment (Vinogradov et al, 2004;Cense et al, 2006). We previously performed high-speed camera (HSC) videography during the exposure of in vitro S. mutans interproximal dental biofilms to high-velocity (60 m/s) impacts from micro water jets and sprays using an interdental cleaning device [Air-Floss (AF), Philips] (Rmaile et al, 2013;2015;Fabbri et al, 2015). We demonstrated that biofilms exhibited fluid-like behaviour on the order of milliseconds in response (Fabbri et al, 2015).…”

“…We previously performed high-speed camera (HSC) videography during the exposure of in vitro S. mutans interproximal dental biofilms to high-velocity (60 m/s) impacts from micro water jets and sprays using an interdental cleaning device [Air-Floss (AF), Philips] (Rmaile et al, 2013;2015;Fabbri et al, 2015). We demonstrated that biofilms exhibited fluid-like behaviour on the order of milliseconds in response (Fabbri et al, 2015). The videos not only recorded a quasi-instant biofilm fluidisation, but also suggested the formation of migratory ripple-like structures.…”

Targeting microbial biofilms: current and prospective therapeutic strategies

“…High-speed imaging has provided important information on fluid-biofilm-surface interactions and show that although a statistically significant amount of biofilm is removed from the area, the biofilm becomes fluidized and spreads across the surface 17 . The ability of biofilms to become fluidized probably explains the tenacity of bacteria on surfaces after pulsed lavage 18 and may contribute to the low success rate of irrigation and debridement alone in treating periprosthetic infections.…”

High-Velocity Microsprays Enhance Antimicrobial Activity in Streptococcus mutans Biofilms

“…and a wider killing zone around the zone of clearance (Appendix Figure 2). The microspray used in our experiments was a turbulent complex twophase burst of water and air which lasted 60 ms (Fabbri et al 2016). Once the spray impacts the surface, the flow can be divided in two regions: an impingement region in the centre of the impact followed by a two-phase wall-jet region where the flow spreads radially outward.…”