A tripartite toxin-antitoxin module induced by quorum sensing is associated with the persistence phenotype in Streptococcus mutans.

The oral pathogen Streptococcus mutans communicates using a canonical Gram-positive quorum sensing system, CSP-ComDE. The CSP pheromone already known to be involved in the development of genetic competence positively influences the formation of persisters, dormant variants of regular cells that are highly tolerant to antimicrobial therapy. It is now believed that the persistence phenotype is the end result of a stochastic switch in the expression of toxin-antitoxin (TA) modules. TAs consist of a pair of genes that encode two components, a stable toxin and its cognate labile antitoxin. Transcription analyses revealed that three core genes encoding a putative TA system, called SmuATR, were members of the S. mutans CSP regulon. We hypothesized that S. mutans is using its CSP-ComDE system as a deterministic mechanism for persister formation through the activation of smuATR locus. We showed here that the SmuATR system constitutes a novel tripartite type II TA system in which the smuA and smuT genes encode an antitoxin and a toxin, respectively, while SmuR is a transcriptional repressor involved in the autoregulation of the operon. Ectopic expression of SmuA - SmuT is associated with the CSP-inducible persistence phenotype. In contrast, overexpression of SmuT alone is bactericidal and causes membrane permeabilization. To our knowledge, SmuATR is the first functional chromosomal tripartite TA system shown to be induced by the bacterial quorum sensing system and involved in persister formation.

Anthocyanin incorporated dental copolymer: bacterial growth inhibition, mechanical properties, and compound release rates and stability by (1)h NMR.

Objective. To evaluate bacterial growth inhibition, mechanical properties, and compound release rate and stability of copolymers incorporated with anthocyanin (ACY; Vaccinium macrocarpon). Methods. Resin samples were prepared (Bis-GMA/TEGDMA at 70/30 mol%) and incorporated with 2 w/w% of either ACY or chlorhexidine (CHX), except for the control group. Samples were individually immersed in a bacterial culture (Streptococcus mutans) for 24 h. Cell viability (n = 3) was assessed by counting the number of colony forming units on replica agar plates. Flexural strength (FS) and elastic modulus (E) were tested on a universal testing machine (n = 8). Compound release and chemical stability were evaluated by UV spectrophotometry and (1)H NMR (n = 3). Data were analyzed by one-way ANOVA and Tukey's test ( α = 0.05). Results. Both compounds inhibited S. mutans growth, with CHX being most effective (P < 0.05). Control resin had the lowest FS and E values, followed by ACY and CHX, with statistical difference between control and CHX groups for both mechanical properties (P < 0.05). The 24 h compound release rates were ACY: 1.33 µg/mL and CHX: 1.92 µg/mL. (1)H NMR spectra suggests that both compounds remained stable after being released in water. Conclusion. The present findings indicate that anthocyanins might be used as a natural antibacterial agent in resin based materials.

Catechin-incorporated dental copolymers inhibit growth of Streptococcus mutans.

OBJECTIVE: To test the inhibitory growth activity of green tea catechin incorporated into dental resins compared to resins containing the broad-spectrum antimicrobial compound chlorhexidine against Streptococcus mutans in vitro. MATERIAL AND METHODS: The minimum inhibitory concentrations (MICs) of epigallocatechin-gallate (EGCg) and chlorhexidine (CHX) were determined according to the microdilution method. Resin discs (5 mm × 3 mm) were prepared from Bis-GMA/TEGDMA (R1) and Bis-GMA/CH3Bis-GMA (R2) comonomers (n=9) containing: a) no drug, b) EGCg, c) CHX. Two concentrations of each drug (0.5× MIC and 1× MIC) were incorporated into the resin discs. Samples were individually immersed in a bacterial culture and incubated for 24 h at 37°C under constant agitation. Cell viability was assessed by counting the number of colonies on replica agar plates. Statistical analysis was performed using one-way ANOVA, Tukey and Student t-tests (α=0.05). RESULTS: Both resins containing EGCg and CHX showed a significant inhibition of bacterial growth at both concentrations tested (p<0.05). A significantly higher inhibition was observed in response to resins containing CHX at 0.5× MIC and 1× MIC, and EGCg at 1× MIC when compared to EGCg at 0.5× MIC. Also, EGCg at 0.5× MIC in R1 had a significantly higher growth inhibition than in R2. CONCLUSIONS: Both EGCg and CHX retained their antibacterial activity when incorporated into the resin matrix. EGCg at 1× MIC in R1 and R2 resins significantly reduced S. mutans survival at a level similar to CHX. The data generated from this study will provide advances in the field of bioactive dental materials with the potential of improving the lifespan of resin-based restorations.

Catechin-incorporated dental copolymers inhibit growth of Streptococcus mutans

Objective: To test the inhibitory growth activity of green tea catechin incorporated into dental resins compared to resins containing the broad-spectrum antimicrobial compound chlorhexidine against Streptococcus mutans in vitro. Material and Methods: The minimum inhibitory concentrations (MICs) of epigallocatechin-gallate (EGCg) and chlorhexidine (CHX) were determined according to the microdilution method. Resin discs (5 mm × 3 mm) were prepared from Bis-GMA/TEGDMA (R1) and Bis-GMA/CH3Bis-GMA (R2) comonomers (n=9) containing: a) no drug, b) EGCg, c) CHX. Two concentrations of each drug (0.5× MIC and 1× MIC) were incorporated into the resin discs. Samples were individually immersed in a bacterial culture and incubated for 24 h at 37°C under constant agitation. Cell viability was assessed by counting the number of colonies on replica agar plates. Statistical analysis was performed using one-way ANOVA, Tukey and Student t-tests (α=0.05). Results: Both resins containing EGCg and CHX showed a significant inhibition of bacterial growth at both concentrations tested (p<0.05). A significantly higher inhibition was observed in response to resins containing CHX at 0.5× MIC and 1× MIC, and EGCg at 1× MIC when compared to EGCg at 0.5× MIC. Also, EGCg at 0.5× MIC in R1 had a significantly higher growth inhibition than in R2. Conclusions: Both EGCg and CHX retained their antibacterial activity when incorporated into the resin matrix. EGCg at 1× MIC in R1 and R2 resins significantly reduced S. mutans survival at a level similar to CHX. The data generated from this study will provide advances in the field of bioactive dental materials with the potential of improving the lifespan of resin-based restorations.