Antimicrobial Activity of Cinnamaldehyde on Streptococcus mutans Biofilms.

Zhiyan He,Zhengwei Huang,Wei Zhou,Wei Jiang

doi:10.3389/fmicb.2019.02241

Zhiyan He, Zhengwei Huang + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2019.02241

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Abstract

Streptococcus mutans is considered the most relevant bacteria in the transition of non-pathogenic commensal oral microbiota to biofilms which contribute to the dental caries process. The present study aimed to evaluate the antimicrobial activity of a natural plant product, cinnamaldehyde against S. mutans biofilms. Minimum inhibitory concentrations (MIC), minimal bactericidal concentration (MBC), and growth curves were determined to assess its antimicrobial effect against planktonic S. mutans. The biofilm biomass and metabolism with different concentrations of cinnamaldehyde and different incubation time points were assessed using the crystal violet and MTT assays. The biofilms were visualized using confocal laser scanning microscopy (CLSM). Bacterial cell surface hydrophobicity, aggregation, acid production, and acid tolerance were evaluated after cinnamaldehyde treatment. The gene expression of virulence-related factors (gtfB, gtfC, gtfD, gbpB, comDE, vicR, ciaH, ldh and relA) was investigated by real-time PCR. The MIC and MBC of cinnamaldehyde against planktonic S. mutans were 1000 and 2000 μg/mL, respectively. The results showed that cinnamaldehyde can decrease biofilm biomass and metabolism at sub-MIC concentrations. CLSM images revealed that the biofilm-covered surface areas decreased with increasing concentrations of cinnamaldehyde. Cinnamaldehyde increased cell surface hydrophobicity, reduced S. mutans aggregation, inhibited acid production, and acid tolerance. Genes expressions in the biofilms were down-regulated in the presence of cinnamaldehyde. Therefore, our data demonstrated that cinnamaldehyde at sub-MIC level suppressed the microbial activity on S. mutans biofilm by modulating hydrophobicity, aggregation, acid production, acid tolerance, and virulence gene expression.

Highlights

Dental caries is a disease of chronic progressive destruction that occurs as a result of dysbiosis among commensal and pathogenic bacteria
The overall biomass of biofilms was quantified by the crystal violet (CV) assay at the concentration ranging up to 500 μg/mL of
Cinnamaldehyde inhibited the metabolic activity of dualspecies biofilm in a manner similar to its inhibition of the S. mutans single-species biofilm (Figure 2D). These results demonstrated that cinnamaldehyde at the concentrations ranging from 125 to 500 μg/mL can effectively reduce biofilm biomass and metabolic activity of S. mutans single and dual-species biofilms at different incubation time points during biofilm formation

Summary

Introduction

Dental caries is a disease of chronic progressive destruction that occurs as a result of dysbiosis among commensal and pathogenic bacteria. Streptococcus mutans, a Gram-positive bacterium in oral cavity, causes dysbiosis in this symbiotic ecosystem, it is not solely responsible for the disease progression It is considered as the most relevant bacteria in the transition of non-pathogenic commensal oral microbiota to biofilms which contribute to the dental caries process (Martins et al, 2018). S. mutans has developed multiple mechanisms to colonize the tooth surface and form bacterial plaque biofilm (Ren et al, 2016; Hu et al, 2018b) The ability of this bacterium to produce organic acids through various carbohydrate metabolism processes (acidogenicity) and survive in low pH environment (aciduricity) are major virulence factors in biofilm and lead to the development to dental caries (Cai et al, 2017; Chakraborty and Burne, 2017). Since reckless and continuous use of antibiotics has led to a rapid increase in antibiotic resistance to conventional therapies, there is an urgent need to develop novel antimicrobial agents in order to inhibit biofilm formation

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