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

S Fabbri,D.A Johnston,A Rmaile,B Gottenbos,M De Jager,M Aspiras,E.M Starke,M.T Ward,P Stoodley

doi:10.1016/j.jmbbm.2015.12.012

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.

Highlights

Dental plaque biofilms are the heterogeneous bacterial communities attached to teeth and soft tissues and embedded in a matrix composed mainly of extracellular DNA, proteins, and polysaccharides (Marsh and Bradshaw, 1995)
Fluid shear stresses generated via either non-contact toothbrushing or fluid flow play a major role in biofilm detachment (Hope et al, 2003; Hope and Wilson, 2003; Paramonova et al, 2009) since dental plaque mainly accumulates in particular areas inside the mouth (such as pits, fissures, interproximal (IP) spaces and subgingival areas) inaccessible for toothbrush bristles and dentifrices (Fried, 2012)
Mucins have been shown to be important in the adhesion of S. mutans, in both promoting attachment (Kishimoto et al, 1989) or inhibiting attachment and biofilm formation (Frenkel and Ribbeck, 2015; Marsh et al, 2009) we found the presence of mucin as a slide preconditioned pellicle or in the growth medium had no significant effect on rigidity (p40.05), suggesting that it did not influence matrix production, or was not incorporated at all into the matrix

Summary

Introduction

Dental plaque biofilms are the heterogeneous bacterial communities attached to teeth and soft tissues and embedded in a matrix composed mainly of extracellular DNA, proteins, and polysaccharides (Marsh and Bradshaw, 1995). When biofilms are subjected to different flow conditions, they mechanically behave as viscoelastic fluids (Klapper et al, 2002; Peterson et al, 2015; Towler et al, 2003; Wilking et al, 2011). This means that at low-shear rates biofioms have a “solid-like” behaviour and are able to store energy, while at high-shear rates they become “fluid-like” and lose their ability to store elastic energy. Mechanical biofilm removal either using low volume, high-velocity water droplets (Cense et al, 2006) or by entrained air bubbles (Parini and Pitt, 2006; Sharma et al, 2005b) has shown positive results due to the droplets' impact pressure, hydrodynamic shear stresses and the surface tension effects of the passage of an air–water interface over a solid surface (Busscher et al, 2010b)

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Discussion

Conclusion