ComCED signal loop precisely regulates nlmC expression in Streptococcus mutans

Combinatorial effects of trans-cinnamaldehyde with fluoride and chlorhexidine on Streptococcus mutans

AIMS

The aim of this study was to investigate the effects of trans-cinnamaldehyde (TC) and its synergistic activity with chlorhexidine (CHX) and fluoride against Streptococcus mutans.

METHODS AND RESULTS

Streptococcus mutans UA159 was treated with TC alone and in combination with CHX or sodium fluoride. The synergy profile was analysed using the Zero Interaction Potency model. TC showed strong synergism (synergy score of 21·697) with CHX, but additive effect (synergy score of 5·298) with fluoride. TC and the combinations were tested for acid production (glycolytic pH drop) and biofilm formation by S. mutans, and nitric oxide production in macrophages. TC significantly inhibited sucrose-dependent biofilm formation and acid production by S. mutans. Mechanistic studies were carried out by qRT-PCR-based transcriptomic studies which showed that TC acts by impairing genes related to metabolism, quorum sensing, bacteriocin expression, stress tolerance and biofilm formation.

CONCLUSIONS

trans-Cinnamaldehyde potentiates CHX and sodium fluoride in inhibiting S. mutans biofilms and virulence through multiple mechanisms. This study sheds significant new light on the potential to develop TC as an anti-caries treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Oral diseases were classified as a 'silent epidemic' in the US Surgeon General's Report on Oral Health. Two decades later, >4 billion people are still affected worldwide by caries, having significant effects on the quality of life. There is an urgent need to develop novel compounds and strategies to combat dental caries. Here, we prove that TC downregulates multiple pathways and potentiates the CHX and fluoride to prevent S. mutans biofilms and virulence. This study sheds significant new light on the potential to develop TC in combination with CHX or fluoride as novel treatments to arrest dental caries.

ABC Transporter CslAB, a Stabilizer of ComCDE Signal in Streptococcus mutans

Background:

In Streptococcus mutans, ComCDE, a peptide-induced two-component signal transduction system, forms a closed signal transduction, and even if difunctional ComE closes this signal at its headstream to avoid its infinite amplification, it is not enough for ComE to work in a concentration-dependent manner. CslAB has a chance to regulate ComCDE by controlling extracellular competence-stimulating peptide (CSP) concentration through its processing and secretion.

Objectives:

To first confirm the binding properties of cslAB promoter (PcslAB) with ComE, then to uncover in vivo need of cslAB expression, and finally to unveil the role of CslAB.

Materials and Methods:

Electrophoretic mobility shift assay was used to confirm the binding properties of PcslAB with ComE. In vivo cslAB transcription was detected by β-galactosidase activity because its gene has been fused to cslAB operon, and finally the role of CslAB was reviewed.

Results:

PcslAB is a weak promoter responding to ComE and its binding appears to be negative cooperative. Although PcslAB is partially controlled by ComCDE, it can respond to ComCDE regulation. Supported by the obtained molecular evidence, CslAB acts as a stabilizer of ComCDE signal on the patterns of its expression.

Conclusions:

PcslAB is partially controlled by ComCDE. CslAB is a stabilizer of ComCDE signal to ensure that ComE works in a concentration-dependent manner.