Evaluating hop extract concentrations found in commercial beer to inhibit Streptococcus mutans biofilm formation.

AIMS: The purpose of this study was to compare the effect of hop extracts with diverse ß-acid concentrations on Streptococcus mutans biofilm formation. METHODS AND RESULTS: Ten different hop extracts, with α-acid concentrations similar to those found in commercial beer products and ß-acid concentrations ranging from 2.6 to 8.1%, were added to distilled water to make standardized concentrations. S. mutans isolates were treated with hop extract dilutions varying from 1:2 to 1:256. The minimum inhibitory, minimum bactericidal and minimum biofilm inhibitory concentrations were determined and the optical density was evaluated. Live/dead staining confirmed the bactericidal effects. Biofilm formation of several strains of S. mutans was significantly inhibited by hop extract dilutions of 1:2, 1:4, 1:8, 1:16 and 1:32. Strong negative correlations were observed between α- and ß-acid concentrations of the hop extracts and S. mutans total growth and biofilm formation. CONCLUSIONS: The use of hop extracts prepared similarly to commercial beer decreased S. mutans biofilm formation. SIGNIFICANCE AND IMPACT OF THE STUDY: The inclusion of hops in the commercial beer products may provide beneficial health effects. Further studies are warranted to determine an effect in vivo on the development of dental caries.

Effect of phototherapy on the metabolism of Streptococcus mutans biofilm based on a colorimetric tetrazolium assay.

The aim of this in vitro study was to determine the effect of violet-blue light on the metabolic activity of early Streptococcus mutans biofilm, reincubated at 0, 2, and 6 h after 5 min of violet-blue light treatment. S. mutans UA159 biofilm cells were cultured for 12 to 16 h in microtiter plates with Tryptic Soy broth (TSB) or TSB with 1% sucrose (TSBS) and irradiated with violet-blue light for 5 min. After irradiation, the plates were reincubated at 37°C for 0, 2, or 6 h in 5% CO2. Colorimetric tetrazolium salt reduction assay was used to investigate bacterial metabolic activity. Mixed model ANOVA was used to find the difference between the violet-blue light treated and nontreated groups. Bacterial metabolic activity was significantly lower in the violet-blue light group for TSB than in the nontreated group (P < 0.0001) regardless of recovery time. However, the differences between metabolic activity in the treated groups without sucrose decreased over time. For TSBS, metabolic activity was significantly lower with violet-blue light at 0 and 2 h. Violet-blue light inhibited the metabolic activity of S. mutans biofilm cells in the light-treated group. This finding may present a unique treatment method for patients with active caries.

Photo Inactivation of Streptococcus mutans Biofilm by Violet-Blue light.

Among various preventive approaches, non-invasive phototherapy/photodynamic therapy is one of the methods used to control oral biofilm. Studies indicate that light at specific wavelengths has a potent antibacterial effect. The objective of this study was to determine the effectiveness of violet-blue light at 380-440 nm to inhibit biofilm formation of Streptococcus mutans or kill S. mutans. S. mutans UA159 biofilm cells were grown for 12-16 h in 96-well flat-bottom microtiter plates using tryptic soy broth (TSB) or TSB with 1 % sucrose (TSBS). Biofilm was irradiated with violet-blue light for 5 min. After exposure, plates were re-incubated at 37 °C for either 2 or 6 h to allow the bacteria to recover. A crystal violet biofilm assay was used to determine relative densities of the biofilm cells grown in TSB, but not in TSBS, exposed to violet-blue light. The results indicated a statistically significant (P < 0.05) decrease compared to the non-treated groups after the 2 or 6 h recovery period. Growth rates of planktonic and biofilm cells indicated a significant reduction in the growth rate of the violet-blue light-treated groups grown in TSB and TSBS. Biofilm viability assays confirmed a statistically significant difference between violet-blue light-treated and non-treated groups in TSB and TSBS. Visible violet-blue light of the electromagnetic spectrum has the ability to inhibit S. mutans growth and reduce the formation of S. mutans biofilm. This in vitro study demonstrated that violet-blue light has the capacity to inhibit S. mutans biofilm formation. Potential clinical applications of light therapy in the future remain bright in preventing the development and progression of dental caries.