Mechanistic insights into the inhibitory effect of theaflavins on virulence factors production in Streptococcus mutans.

Streptococcus mutans is the primary etiological agent associated with cariogenic process. The present study aimed to investigate the antibacterial and anti-virulence activities of theaflavins (TFs) to Streptococcus mutans UA159 as well as the underlying mechanisms. The results showed that TFs were capable of suppressing the acid production, cell adherence, water-insoluble exopolysaccharides production, and biofilm formation by S. mutans UA159 with a dosage-dependent manner while without influencing the cell growth. By a genome-wide transcriptome analysis (RNA-seq), we found that TFs attenuated the biofilm formation of S. mutans UA159 by inhibiting glucosyltransferases activity and the production of glucan-binding proteins (GbpB and GbpC) instead of directly blocking the expression of genes coding for glucosyltransferases. Further, TFs inhibited the expression of genes implicated in peptidoglycan synthesis, glycolysis, lipid synthesis, two-component system, signaling peptide transport (comA), oxidative stress response, and DNA replication and repair, suggesting that TFs suppressed the virulence factors of S. mutans UA159 by affecting the signal transduction and cell envelope stability, and weakening the ability of cells on oxidative stress resistance. In addition, an upregulated expression of the genes involved in protein biosynthesis, amino acid metabolism, and transport system upon TFs treatment indicated that cells increase the protein synthesis and nutrients uptake as one self-protective mechanism to cope with stress caused by TFs. The results of this study increase our current understanding of the anti-virulence activity of TFs on S. mutans and provide clues for the use of TFs in the prevention of dental caries.

Tooth brushing using toothpaste containing theaflavins reduces the oral pathogenic bacteria in healthy adults.

Theaflavins (TFs) are the main bioactive component in black tea. At present, little effort has been done to evaluate the influence of TFs when included in the toothpaste on the diversity of oral microbiota. In this study, eighty samples collected from the saliva and supragingival plaque of 20 healthy adults using toothpaste with the absence or presence of TFs for a period of 4 weeks were used for the oral microbiome analysis by 16S rRNA gene sequencing. Alpha and beta diversity analysis showed that tooth brushing using the toothpaste with TFs significantly increased the microbial abundance in the saliva samples, and altered the oral microbiota obtained from the saliva and supragingival plaque. The linear discriminant analysis revealed that the use of toothpaste with TFs significantly reduced the abundance of oral pathogens (e.g., Prevotella, Selenomonas, and Atopobium) while increased the abundance of oral-health associated bacteria (e.g., Streptococcus and Rothia). In addition, using toothpaste with TFs reduced the functional pathways abundance relevance to the extracellular polymeric substance (EPS) synthesis while enriched the functions in transporters, ABC transporters, two-component system, and amino acid metabolism. Collectively, our results provide evidence for the application of toothpaste containing TFs as a promising oral care product. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02699-7.

New insights into the antibacterial and quorum sensing inhibition mechanism of Artemisia argyi leaf extracts towards Pseudomonas aeruginosa PAO1.

This study aimed to investigate the anti-quorum sensing (QS) activity of Artemisia argyi leaf extracts (AALE) towards Pseudomonas aeruginosa PAO1 as well as the underlying molecular mechanisms. Using a biosensor Chromobacterium violaceum CV026, AALE were found to have anti-QS activity as AALE treatment significantly inhibited the violacein production of C. violaceum CV026 while produced little effect on the cell growth. Beyond that a higher dosage of AALE inhibited cell growth, sub-MIC of AALE significantly reduced the production of QS-regulated virulence factors (pyocyanin, elastase, and rhamnolipid), biofilm formation, and the swarming and swimming motility in P. aeruginosa PAO1 with a dosage-dependent manner. Quantitative real-time PCR (qRT-PCR) analysis did not detect the direct inhibitory effect of AALE on the expression of QS genes (lasI, lasR, rhlI, and rhlR). By iTRAQ-based quantitative proteomic analysis, 129 proteins were found to be differentially expressed upon AALE treatment, with 85 upregulated and 44 downregulated proteins, respectively. Functional enrichment analysis of the differential proteins revealed that AALE exerted anti-QS activity towards P. aeruginosa PAO1 by upregulating the expression of the global regulator CsrA, inducing oxidative stress, and perturbing protein homeostasis. Moreover, the inhibitory effect of AALE on the virulence of P. aeruginosa PAO1 was likely to be achieved by attenuating the expression of QS-regulated genes instead of QS genes. Collectively, the results of this study provide a basis for the future use of AALE as a preservative in controlling food spoilage caused by P. aeruginosa. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02663-5.