Inhibition of acid production in Streptococcus mutans R9: inhibition constants and reversibility

Exploration of the Main Antibiofilm Substance of Lactobacillus plantarum ATCC 14917 and Its Effect against Streptococcus mutans

Dental plaque, a complex biofilm system established by cariogenic bacteria such as Streptococcus mutans (S. mutans), is the initiator of dental caries. Studies have found that the cell-free supernatant (CFS) of Lactobacilli could inhibit S. mutans biofilm formation. However, the main antibiofilm substance of the Lactobacilli CFS that acts against S. mutans is unclear. The present study found that the CFS of Lactobacillus plantarum (L. plantarum) ATCC 14917 had the strongest antibiofilm effect among the five tested oral Lactobacilli. Further bioassay-guided isolation was performed to identify the main antibiofilm substance. The antibiofilm effect of the end product, named 1-1-4-3, was observed and the structure of it was elucidated by using Q-TOF MS, 2D NMR and HPLC. The results showed that several components in the CFS had an antibiofilm effect; however, the effect of 1-1-4-3 was the strongest, as it could reduce the generation of exopolysaccharides and make the biofilm looser and thinner. After structure elucidation and validation, 1-1-4-3 was identified as a mixture of lactic acid (LA) and valine. Additionally, LA was shown to be the main antibiofilm substance in 1-1-4-3. In summary, this study found that the antibiofilm effect of the L. plantarum CFS against S. mutans was attributable to the comprehensive effect of multiple components, among which LA played a dominant role.

Sustainable multifunctional phenolic lipids as potential therapeutics in Dentistry

Phenolic lipids components of the cashew nutshell liquid (CNSL) have molecular structures capable of chemical signalling that regulate gene expression, metabolism and inflammation. This study sets out to assess how CNSL derivatives impact oral bacteria, from an antibacterial and anti-collagenolytic perspective, as well as its biocompatibility with dental pulp stem cells. Two hemi-synthetic saturated CNSL derivative compounds were selected (LDT11-Anacardic Acids-derivative and LDT409-cardanol-derivative). Bacteriostatic activity was tested against Streptococcus mutans and Veillonella parvula. Antimicrobial capacity against preformed S. mutans biofilms was investigated using a collagen-coated Calgary Biofilm Device and confocal microscopy. Clostridium histolyticum, P. gingivalis and S. mutans biofilms were used to assess anti-collagenolytic activity. Biocompatibility with human dental pulp stromal cells (HDPSCs) was investigated (MTT for viability proportion, LDH assays for cell death rate). LDTs inhibited the bacterial growth, as well as partially inhibited bacterial collagenases in concentrations higher than 5 μg/mL. Dose–response rates of biofilm cell death was observed (LDT11 at 20, 50, 100 μg/mL = 1.0 ± 0.4, 0.7 ± 0.3, 0.6 ± 0.03, respectively). Maximum cytotoxicity was 30%. After 1 week, LDT409 had no HDPSCs death. HDPSCs viability was decreased after 24 h of treatment with LDT11 and LDT409, but recovered at 72 h and showed a massive increase in viability and proliferation after 1 week. LDTs treatment was associated with odontoblast-like morphology. In conclusion, LDT11 multifunctionality and biocompatibility, stimulating dental pulp stem cells proliferation and differentiation, indicates a potential as a bio-based dental material for regenerative Dentistry. Its potential as a bacterial collagenases inhibitor to reduce collagen degradation in root/dentinal caries can be further explored.

Acetate and ethanol production from H2 and CO2by Moorella sp. using a repeated batch culture

The growth inhibition of Moorella sp. HUC22-1 by undissociated acetic acid was analyzed using a non-competitive inhibition model coupled with a pH inhibition model. In the cells grown on H2 and CO2, the inhibition constant, K(p) of the undissociated acetic acid was 6.2 mM (164 mM as the total acetate at pH 6.2, pKa = 4.795, 55 degrees C), which was 1.5-fold higher than that obtained in cells grown on fructose. When a pH-controlled batch culture was performed using a fermentor at pH 6.2 with H2 and CO2, a maximum of 0.92 g/l of dry cell weight and 339 mM of acetate were produced after 220 h, which were 4.4- and 6.8-fold higher than those produced in the pH-uncontrolled batch culture, respectively. In order to reduce acetate inhibition in the culture medium, a repeated batch culture with cell recycling was performed at a constant pH with H2 and CO2. At a pH of 6.2, the total acetate production reached 840 mmol/l-reactor with 4.7 mmol/l-reactor of total ethanol production after 420 h. When the culture pH was maintained at 5.8, which was the optimum for ethanol production, the total ethanol production reached 15.4 mmol/l-reactor after 430 h, although the total acetate production was decreased to 675 mmol/l-reactor.

Inhibition of acid production in Streptococcus mutans R9 by formic acid

Both lactic and acetic acids cause mixed inhibition of acid production in mutans streptococci. This inhibition is partly irreversible due to cell death, an important factor when considering acidogenicity and aciduricity of these organisms, and their role in the caries process. Other monocarboxylic end-products may be present and may also be important inhibitors of acid production in dental plaque. This study considered the effects of varying concentrations of the end-product formic acid on acid production rates in Streptococcus mutans R9, measured using the pH-stat. Undissociated formic acid caused mixed inhibition with constants of Kiu (uncompetitive) of 6.07 +/- 1.27 mmol-1 and Kic (competitive) of 0.2 +/- 0.11 mmol l-1. Inhibition was found to be fully reversible, with no loss of cell viability. It is concluded that at those concentrations found in vivo, formate is not a significant inhibitor of acid production by S. mutans in dental plaque at any time, and is not important in determining the acidogenicity or aciduricity of this organism.