The specific degree-of-polymerization of A-type proanthocyanidin oligomers impacts Streptococcus mutans glucan-mediated adhesion and transcriptome responses within biofilms

Guoping Feng,Marlise I Klein,Stacy Gregoire,Ajay P Singh,Nicholi Vorsa,Hyun Koo

doi:10.1080/08927014.2013.794456

Guoping Feng, Marlise I Klein + Show 4 more

Open Access

https://doi.org/10.1080/08927014.2013.794456

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Abstract

Cranberry A-type proanthocyanidins (PACs) have been recognized for their inhibitory activity against bacterial adhesion and biofilm-derived infections. However, the precise identification of the specific classes of degree-of-polymerization (DP) conferring PACs bioactivity remains a major challenge owing to the complex chemistry of these flavonoids. In this study, chemically characterized cranberries were used in a multistep separation and structure-determination technique to isolate A-type PAC oligomers of defined DP. The influences of PACs on the 3D architecture of biofilms and Streptococcus mutans-transcriptome responses within biofilms were investigated. Treatment regimens that simulated topical exposures experienced clinically (twice-daily, 60 s each) were used over a saliva-coated hydroxyapatite biofilm model. Biofilm accumulation was impaired, while specific genes involved in the adhesion of bacteria, acid stress tolerance, and glycolysis were affected by the topical treatments (vs the vehicle-control). Genes (rmpC, mepA, sdcBB, and gbpC) associated with sucrose-dependent binding of bacteria were repressed by PACs. PACs of DP 4 and particularly DP 8 to 13 were the most effective in disrupting bacterial adhesion to glucan-coated apatitic surface (>85% inhibition vs vehicle control), and gene expression (eg rmpC). This study identified putative molecular targets of A-type cranberry PACs in S. mutans while demonstrating that PAC oligomers with a specific DP may be effective in disrupting the assembly of cariogenic biofilms.

Highlights

Biofilms are highly organized and structured microbial communities enmeshed in an extracellular matrix comprised of mainly polysaccharides and proteins (Flemming and Wingender 2010)
All compounds were dissolved in 15% ethanol in 2.5 mM potassium phosphate buffer, which was used as a vehicle control; treatments with 15% ethanol did not affect the viability of S. mutans biofilm cells when compared to untreated S. mutans biofilms
The biomass and thickness of both EPS and adherent bacteria in PACs-treated biofilms were significantly less than in vehicle-treated biofilms (Table 2), which resulted in defective biofilm accumulation and altered 3D architecture (Figure 2)

Summary

Introduction

Biofilms are highly organized and structured microbial communities enmeshed in an extracellular matrix comprised of mainly polysaccharides and proteins (Flemming and Wingender 2010). Previous studies have shown that PACs-containing extract is highly effective in inhibiting the EPS synthesis by surface-adsorbed Gtfs, and impaired the accumulation of S. mutans biofilms on apatitic surfaces (Duarte et al 2006). We detected 119 genes whose expression was differentially regulated in response to PACs. To evaluate the data generated from microarray and RTqPCR analysis, genes were organized into categories relevant to S. mutans biofilm formation, fitness and virulence expression (see Materials and Methods).

Results

Conclusion