A Multi-scale Biophysical Approach to Develop Structure-Property Relationships in Oral Biofilms

J Pattem,L Bozec,E Allan,S Aguayo,D Spratt,M Davrandi

doi:10.1038/s41598-018-23798-1

J Pattem, L Bozec + Show 4 more

Open Access

https://doi.org/10.1038/s41598-018-23798-1

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Abstract

Over the last 5–10 years, optical coherence tomography (OCT) and atomic force microscopy (AFM) have been individually applied to monitor the morphological and mechanical properties of various single-species biofilms respectively. This investigation looked to combine OCT and AFM as a multi-scale approach to understand the role sucrose concentration and age play in the morphological and mechanical properties of oral, microcosm biofilms, in-vitro. Biofilms with low (0.1% w/v) and high (5% w/v) sucrose concentrations were grown on hydroxyapatite (HAP) discs from pooled human saliva and incubated for 3 and 5 days. Distinct mesoscale features of biofilms such as regions of low and high extracellular polymeric substances (EPS) were identified through observations made by OCT. Mechanical analysis revealed increasing sucrose concentration decreased Young’s modulus and increased cantilever adhesion (p < 0.0001), relative to the biofilm. Increasing age was found to decrease adhesion only (p < 0.0001). This was due to mechanical interactions between the indenter and the biofilm increasing as a function of increased EPS content, due to increasing sucrose. An expected decrease in EPS cantilever contact decreased adhesion due to bacteria proliferation with biofilm age. The application OCT and AFM revealed new structure-property relationships in oral biofilms, unattainable if the techniques were used independently.

Highlights

Oral biofilms are complex microbial communities[1], embedded in a matrix of extracellular polymeric substances (EPS)[2,3]
optical coherence tomography (OCT) imaging and scattering intensity profiling were applied to biofilms cultivated on HAP discs with increasing sucrose concentration and age, under static phosphate buffered saline (PBS) conditions
We hypothesize that areas of low optical density have a high EPS to bacteria ratio, while areas of low density have a high bacteria to EPS ratio

Summary

Introduction

Oral biofilms are complex microbial communities[1], embedded in a matrix of extracellular polymeric substances (EPS)[2,3]. Applying techniques that span a range of length scales, are capable of in-vitro analysis and preserve biofilm structural and mechanical integrity are vital in the development of structure-property relationships. Binding assays such as fluorescence staining have enabled researchers to extensively investigate a biofilms microbiology with increasing detail since the 1980′s10,11. Common characterization methods include scanning electron microscopy (SEM)[13,14,15] and confocal laser scanning microscopy (CLSM)[15,16] These techniques only provide basic morphology and quantitative live – dead ratios respectively[16]. It has been used to determine the morpho-mechanical profiles of single bacterial species and cells with success[23,24]

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