High-Velocity Microsprays Enhance Antimicrobial Activity in Streptococcus mutans Biofilms

Abstract

Streptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm's complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. We assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-days old S. mutans biofilms.Biofilms were exposed to a 90° or 30° impact, firstly using a 1-µm tracer beads solution (10 9 beads/mL) and secondly, a 0.2% Chlorhexidine (CHX) or 0.085% Cetylpyridinium chloride (CPC) solution. For comparison, a 30-sec diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth (RD) into the biofilm. Assessment of antimicrobial penetration was determined by calculating the killing depth (KD) detected by live/dead viability staining. We firstly demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared to diffusion and mouthwashing exposures. Next our experiments revealed that the microspray yielded better antimicrobial penetration evidenced by deeper killing inside the biofilm and a wider killing zone around the zone of clearance than a diffusion transport with the same antimicrobials. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 20% more bacteria killing (for both CHX and CPC) than the 90 o impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver microparticles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm/burst interface might have enhanced beads and antimicrobials delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents' delivery inside biofilm in those protected areas where some biofilm might remain.3

Fluid‐driven interfacial instabilities and turbulence in bacterial biofilms

“…Fluid/structure interactions in biofilms are known to modulate the dynamics of biofilm growth, tolerance to antibiotics and virulence. This phenomenon might also explain our recent finding that high‐velocity water sprays more effectively delivered microbeads and antimicrobials into in vitro dental biofilms (Fabbri et al ., ). Interfacial instabilities in biofilms may enhance mass and heat transport (Chen et al ., ; Vazquez‐Una et al ., ).…”

Computational Investigation of Ripple Dynamics in Biofilms in Flowing Systems

“…Previously, we had developed a channel system (28) to study the removal of dental biofilms by high velocity air jets and water sprays. Briefly, a flow channel was created by inserting two biofilm-colonized glass microscope slides in parallel, separated by a distance of 1 mm, into a specially fabricated holder.…”

“…In the linear stability analysis performed previously, we treated the problem as a two-fluid problem in which the external/forcing was treated as a Euler (infinite Reynolds number) flow and the biofilm was treated as a two-phase mixture (28). Here, rather than treating the problem as a sharp interface problem, we consider the diffuse interface problem in which the entire domain consists of the multiphase mixture of network and fluid.…”

“…where Re f is the Reynolds number for the fluid. Based on the relative length, velocity and viscosities, we estimated that the biofilm has a Reynolds number several orders of magnitude less than that of the fluid (e.g., Re n ¼ 0.1 and Re f ¼ 200) (28).…”

Use of an Oxygen Planar Optode to Assess the Effect of High Velocity Microsprays on Oxygen Penetration in a Human Dental Biofilms In-Vitro

“…In a recent in vitro study we reported that a commercial HVM device designed for interproximal cleaning removed signi cant amounts of a S. mutans bio lm, but intriguingly caused the small amount of remaining bio lm to ow, forming interfacial instabilities between the air/water spray and the bio lm [21]. This effect allowed much deeper penetration of particles and antimicrobial agents into the bio lm than could be achieved by shaking at 200 rpm for 30 s alone [22]. We hypothesized that a combination of removal and mixing might disrupt the pathogenic anoxic environment at the base of the bio lm, thus potentially directing the bio lm community from pathogenic to commensal by modifying the environment, rather than purely trying to kill the bio lm bacteria with antimicrobial agents.…”