Role of sortase in Streptococcus mutans under the effect of nicotine

Preventive effects of taxifolin on dental caries in vitro and in vivo

OBJECTIVES

The present study aimed to explore the inhibitory effect of taxifolin (TAX) on Streptococcus mutans (S. mutans) in vitro and evaluated the anti-caries efficacy of TAX in vivo.

DESIGN

The anti-microbial and anti-biofilm properties of TAX were examined on the S. mutans, and the results were preliminarily verified by quantitative real-time PCR. Polarized light microscopy and transverse microradiography were used to detect the effect of TAX on inhibiting enamel demineralization. The effect of TAX on the remineralization of demineralized enamel was analyzed by a microhardness tester, atomic force microscope, and transverse microradiography. The rat dental caries model was constructed to explore the anti-caries effect of TAX in vivo.

RESULTS

The minimum inhibitory concentration of TAX against S. mutans was 1 mg/mL. The 1 mg/mL TAX impeded the biofilm formation, destroyed the biofilm structure, and effectively prevented enamel demineralization caused by S. mutans. Both the 0.5 mg/mL and 1 mg/mL TAX-treated groups exhibited a higher percentage of surface microhardness recovery, along with lower surface roughness, mineral loss, and lesion depth. Additionally, 1 mg/mL TAX demonstrated the ability to inhibit the initiation and progression of caries in rats, while also proving to be biologically safe.

CONCLUSIONS

TAX had a significant inhibitory effect on S. mutans, could inhibit enamel demineralization and promote remineralization of demineralized enamel, and showed a promising anti-caries effect in vivo.

Sodium houttuyfonate inhibits the cariogenic virulence of Streptococcus mutans through the downregulation of VicRK two components pathway

Background

Caries is one of the most common diseases worldwide, and Streptococcus mutans is considered to be the primary cariogenic pathogen of dental caries. Sodium houttuyfonate (SH) has showed potential antibacterial effects, however, its actions and mechanisms on S. mutans and cariogenicity remain unclear and need further study.

Materials and Methods

we investigated the effects of SH on the cariogenic ability of S. mutans, including growth, biofilm formation, exopolysaccharides (EPS) and acid productions. RNA-Seq and mutants' validation were also performed to explore the mechanisms of SH on S. mutans. The dental caries rat model was finally employed to evaluate the anti-caries capabilities of SH.

Results

The MIC of SH against S. mutans was 64 μg/mL. SH inhibited biofilm formation and cariogenic virulence of S. mutans, including EPS and acid productions, in a dose-dependent manner. RNA-seq analysis indicated that SH significantly downregulated the VicRK pathway, a key pathway regulating biofilm formation and EPS generation. The ΔvicK, ASvicR, ΔgtfB and ΔgtfBC mutants were more sensitive to SH, while VicK and VicR overexpression strains OEvicK and OEvicR were more resistant to SH than WT strains, indicating that SH downregulated the VicRK pathway to inhibit the cariogenicity of S. mutans. SH also significantly inhibited the development of dental caries in rats without systematic toxicities. The expressions of S. mutans VicK, VicR, GtfC and GtfD genes from rat plaques were downregulated by SH.

Conclusion

This study suggested SH inhibited the cariogenic virulence of S. mutans through the downregulation of VicRK two components pathway, thereby offering novel insights for clinical caries prevention.

Tobacco-enhanced biofilm formation by Porphyromonas gingivalis and other oral microbes

Microbial biofilms promote pathogenesis by disguising antigens, facilitating immune evasion, providing protection against antibiotics and other antimicrobials and, generally, fostering survival and persistence. Environmental fluxes are known to influence biofilm formation and composition, with recent data suggesting that tobacco and tobacco-derived stimuli are particularly important mediators of biofilm initiation and development in vitro and determinants of polymicrobial communities in vivo. The evidence for tobacco-augmented biofilm formation by oral bacteria, tobacco-induced oral dysbiosis, tobacco-resistance strategies, and bacterial physiology is summarized herein. A general overview is provided alongside specific insights gained through studies of the model and archetypal, anaerobic, Gram-negative oral pathobiont, Porphyromonas gingivalis.

Antibacterial activities of Miang extracts against selected pathogens and the potential of the tannin-free extracts in the growth inhibition of Streptococcus mutans

Bacterial pathogens have remained a major public health concern for several decades. This study investigated the antibacterial activities of Miang extracts (at non-neutral and neutral pH) against Bacillus cereus TISTR 747, Escherichia coli ATCC 22595, Salmonella enterica serovar Typhimurium TISTR 292 and Streptococcus mutans DMST 18777. The potential of Polyvinylpolypyrrolidone (PVPP)-precipitated tannin-free Miang extracts in growth-inhibition of the cariogenic Streptococcus mutans DMST 18777 and its biofilms was also evaluated. The tannin-rich fermented extracts had the best bacterial growth inhibition against S. mutans DMST 18777 with an MIC of 0.29 and 0.72 mg/mL for nonfilamentous fungi (NFP) Miang and filamentous-fungi-processed (FFP) Miang respectively. This observed anti-streptococcal activity still remained after PVPP-mediated precipitation of bioactive tannins especially, in NFP and FFP Miang. Characterization of the PVPP-treated extracts using High performance liquid chromatography quadrupole-time of flight-mass spectrometry (HPLC-QToF-MS) analysis, also offered an insight into probable compound classes responsible for the activities. In addition, Crystal violet-staining also showed better IC50 values for NFP Miang (4.30 ± 0.66 mg/mL) and FFP Miang (12.73 ± 0.11 mg/mL) against S. mutans DMST 18777 biofilms in vitro. Homology modeling and molecular docking analysis using HPLC-MS identified ligands in tannin-free Miang supernatants, was performed against modelled S. mutans DMST 18777 sortase A enzyme. The in silico analysis suggested that the inhibition by NFP and FFP Miang might be attributed to the presence of ellagic acid, flavonoid aglycones, and glycosides. Thus, these Miang extracts could be optimized and explored as natural active pharmaceutical ingredients (NAPIs) for applications in oral hygienic products.

Selenium Nanoparticle Activity against S. mutans Biofilms as a Potential Treatment Alternative for Periodontitis

The disruption of periodontal biofilms and prevailing antimicrobial resistance issues continue to pose a great challenge to the treatment of periodontitis. Here, we report on selenium nanoparticles (SeNPs) as a treatment alternative for periodontitis by determining their antibiofilm activity against S. mutans biofilms and the potential role of particle size in disrupting biofilms. SeNPs were synthesised via a reduction reaction. Various physicochemical characterisations were conducted on the NPs, including size and shape. The microbroth dilution method was used to conduct the biofilm and antibiofilm assay against S. mutans, which was analysed by absorbance. SeNPs displayed hydrodynamic sizes as low as 46 ± 4 nm at a volume ratio of 1:5 (sodium selenite/ascorbic acid) with good monodispersity and stability. Hydrodynamic sizes of SeNPs after resuspension in tryptic soy broth supplemented with 2.5% sucrose (TSB + 2.5% suc.) and incubated at 37 °C for 24 h, ranged from 112 to 263 nm, while the zeta potential values increased to greater than -11 mV. The biofilm assay indicated that S. mutans are weakly adherent, bordering on moderately adherent biofilm producers. The minimum biofilm inhibitory concentration (MBIC) was identified at 500 µg/mL. At a 1000 µg/mL concentration, SeNPs were able to inhibit S. mutan biofilms up to 99.87 ± 2.41% at a volume ratio of 1:1. No correlation was found between antibiofilm activity and particle size; however, antibiofilm activity was proven to be concentration-dependant. SeNPs demonstrate antibiofilm activity and may be useful for further development in treating periodontitis.

A Transcriptional Analysis Showing the Effects of GH12 Combined with Fluoride for Suppressing the Acidogenicity of Streptococcus mutans Biofilms

The acidogenicity of Streptococcus mutans is important for caries development. The antimicrobial peptide GH12 can affect the integrity of cellular membranes and the virulence factors of S. mutans. Combining GH12 and NaF (GF) efficiently controlled the development of caries, but its mechanisms remained unrevealed. This research intended to verify the effects of GF on the acidogenicity of S. mutans biofilms and to reveal the mechanisms. Lactic acid production assays and pH monitoring assays were conducted to investigate the regulatory effects of the GF treatment on the acidogenicity of S. mutans biofilms. RNA sequencing and bioinformatics analyses were conducted to screen the transcriptional profile affected by the GF treatment. The results demonstrated the GF group had significantly less lactic acid and maintained the broth's pH values above 5.0 for longer times. Thereafter, GO/KEGG enrichment analyses and RT-qPCR validation revealed that the GF treatment mainly restrained the expression of genes related to the carbohydrates' internalization and metabolism. Compared with NaF, the GF treatment further downregulated the carbohydrates transportation genes. Moreover, compared with GH12, the GF treatment affected the membrane's integrity more significantly. Generally, GF treatment could arrest the acidogenicity of S. mutans biofilms, mainly through suppressing carbohydrates transportation and inhibiting overall metabolism.

Small molecule targeting amyloid fibrils inhibits Streptococcus mutans biofilm formation

Amyloid fibrils are important scaffold in bacterial biofilms. Streptococcus mutans is an established cariogenic bacteria dwelling within biofilms, and C123 segment of P1 protein is known to form amyloid fibrils in S. mutans biofilms, among which C3 segment could serve as a promising anti-amyloid target due to its critical role in C123-P1 interactions. Recently, small molecules have been found to successfully inhibit biofilms by targeting amyloid fibrils. Thus, our study aimed to screen small molecules targeting C3 segment with the capacity to influence amyloid fibrils and S. mutans biofilms. In silico screening was utilized to discover promising small molecules, which were evaluated for their effects on bacterial cells and amyloid fibrils. We selected 99 small molecules and enrolled 55 small molecules named D1-D55 for crystal violet staining. Notably, D25 selectively inhibit S. mutans biofilms but had no significant influence on biofilms formed by Streptococcus gordonii and Streptococcus sanguinis, and D25 showed no bactericidal effects and low cytotoxicity. In addition, amyloid fibrils in free-floating bacteria, biofilms and purified C123 were quantified with ThT assays, and the differences were not statistically significant in the presence or absence of D25. Morphological changes of amyloid fibrils were visualized with TEM images, where amorphous aggregates were obvious coupled with long and atypical amyloid fibrils. Moreover, amyloid-related genes were upregulated in response to D25. In conclusion, D25 is a promising antimicrobial agent with the capacity to influence amyloid fibrils and inhibit S. mutans biofilms.

Analyses of the Effects of Arginine, Nicotine, Serotype and Collagen-Binding Proteins on Biofilm Development by 33 Strains of Streptococcus mutans

Streptococcus mutans serotype k strains comprise <3% of oral isolates of S. mutans but are prominent in diseased cardiovascular (CV) tissue. Collagen binding protein (CBP) genes, cbm and cnm, are prevalent in serotype k strains and are associated with endothelial cell invasion. Nicotine increases biofilm formation by serotype c strains of S. mutans, but its effects on serotype k strains and strains with CBP are unknown. Saliva contains arginine which alters certain properties of the extracellular polysaccharides (EPS) in S. mutans biofilm. We examined whether nicotine and arginine affect sucrose-induced biofilm of S. mutans serotypes k (n = 23) and c (n = 10) strains with and without CBP genes. Biofilm mass, metabolism, bacterial proliferation, and EPS production were assessed. Nicotine increased biomass and metabolic activity (p < 0.0001); arginine alone had no effect. The presence of a CBP gene (either cbm or cnm) had a significant effect on biofilm production, but serotype did not. Nicotine increased bacterial proliferation and the effect was greater in CBP + strains compared to strains lacking CBP genes. Addition of arginine with nicotine decreased both bacterial mass and EPS compared to biofilm grown in nicotine alone. EPS production was greater in cnm + than cbm + strains (p < 0.0001). Given the findings of S. mutans in diseased CV tissue, a nicotine induced increase in biofilm production by CBP + strains may be a key link between tobacco use and CV diseases.

Microorganisms: crucial players of smokeless tobacco for several health attributes

Global consumption of smokeless tobacco (SLT) reached 300 million users worldwide majorly from middle-income countries. More than 4000 chemical compounds represent it as one of the noxious consumable products by humans. Besides toxicants/carcinogens, the heavy microbial load on smokeless tobacco further keeps human health at higher risk. Several of these inhabitant microbes participate in biofilm formation and secrete endotoxin/mycotoxins and proinflammatory-like molecules, leading to several oral diseases. Tobacco-associated bacteria exhibit their role in tobacco-specific nitrosamines (TSNAs) formation and acetaldehyde production; both are well-documented carcinogens. Moreover, tobacco exhibits the potential to alter the oral microbiome and induce dysbiotic conditions that lead to the onset of several oral and systemic diseases. Traditional cultivation approaches of microbiology provide partial information of microbial communities of a habitat; therefore, microbiomics has now been employed to study the metagenomes of entire microbial communities. In the past 5 years, few NGS-based investigations have revealed that SLT harbors four dominant phyla (Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes) dominating Bacillus spp. and/or Pseudomonas spp. However, functional characterization of their genetic elements will be a more informative attribute to understand the correlation between inhabitant microbial diversity and their relatedness concerning abundance and diseases. This review provides an update on the microbial diversity of SLT and its associated attributes in human health. KEY POINTS: • Heavy microbial load on smokeless tobacco alarms for poor oral hygiene. • Inhabitant microorganisms of SLT participate in TSNA and biofilm formation. • SLTs alter the oral microbiome and causes oral dysbiosis.

d-Alanine metabolic pathway, a potential target for antibacterial drug designing in Enterococcus faecalis

Enterococcus faecalis (E. faecalis) is associated with persistent root canal infection because of its biofilm and various virulence factors. However, E. faecalis exhibits extensive drug resistance. d-Alanine (D-Ala) metabolism is essential for bacterial peptidoglycan biosynthesis. d-cycloserine (DCS), a second line drug used in the treatment of Mycobacterium tuberculosis infection, can inhibit two key enzymes in D-Ala metabolism: alanine racemase and d-alanine-d-alanine ligase. The aim of this study was to evaluate the effect of D-Ala metabolism on E. faecalis growth, cell wall integrity, biofilm formation and virulence gene expression by additional DCS with or without D-Ala. The results showed that DCS inhibited the planktonic growth and biofilm formation of E. faecalis in a dose-dependent manner. Both the minimum inhibitory concentration (MIC) and minimum biofilm inhibition concentration (MBIC) of DCS against E. faecalis were 200 μg/ml, whereas 50 μg/ml of DCS could inhibit planktonic growth and biofilm formation effectively. The addition of DCS also resulted in bacterial cell wall damage, biofilm surface roughness increase and biofilm adhesion force reduction. Moreover, the treatment of DCS downregulated the expression of asa1, esp, efaA, gelE, sprE, fsrB and ace genes. However, all of these inhibitory effects of DCS could be rescued by the addition of exogenous D-Ala. Meanwhile, DCS exhibited no toxicity to HGEs and HOKs. Therefore, D-Ala metabolic pathway in E. faecalis is a potential target for drug designing.

[Effects of antimicrobial peptide GH12 on the morphology and composition of cariogenic three-species biofilm]

OBJECTIVES

To evaluate the effects of antimicrobial peptide GH12 designed de novo on the structure, morphology, and composition of a cariogenic three-species biofilm.

METHODS

The cariogenic three-species biofilm consis-ted of the cariogenic Streptococcus mutans (S. mutans) and commensal bacteria Streptococcus sanguinis (S. sanguinis) and Streptococcus gordonii (S. gordonii). The biofilm was treated using GH12 (2, 4, and 8 mg·L^-1), and untreated biofilm was used as the control. Changes in the morphology and structure of the three-species biofilm were evaluated through crystal violet staining, scanning electron microscopy (SEM), and fluorescent in situ hybridization (FISH). Moreover, S. mutans in the biofilm was selectively cultured, and its colony-forming units were counted.

RESULTS

The biomass and density of the cariogenic three-species biofilm treated with GH12 decreased compared with those of the control. The number of S. mutans decreased gradually and eventually became undetectable, whereas the number of S. gordonii and S. sanguinis increased and became predominant in the biofilm.

CONCLUSIONS

GH12 can reduce the number of S. mutans within the cariogenic three-species biofilm, destroys its integrity, and consequently makes the biofilm easy to remove.

Effect of LongZhang Gargle on Dual-Species Biofilm of Candida albicans and Streptococcus mutans

Bioactive natural products have become a hot spot for oral disease treatments. At the present study, LongZhang Gargle was investigated for its effects on single-species biofilms of Candida albicans and dual-species biofilms of Candida albicans and Streptococcus mutans. Two different models of single and dual-species biofilms were grown in YNBB medium under appropriate conditions. Biofilm biomass, biofilm architecture, and cell activity in biofilms were assessed using Crystal Violet Staining, MTT, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Significant reductions of biofilm biomass and fungus activity were obtained when treated with LongZhang Gargle at 2% (P < 0.05), 4% (P < 0.05), and 8% (P < 0.05) in single-species biofilms of C. albicans, and at 4% (P < 0.05) and 8% (P < 0.05) in double-species biofilms. Suppression of density, thickness, and the proportion of hyphae and fungal spores were obtained under SEM and CLSM. In conclusion, LongZhang Gargle affects single and dual-species biofilms by inhibiting biofilm biomass, cell activity, and formation of hyphae, but it does not affect the production of Extracellular polysaccharides (EPS). We speculate that LongZhang Gargle would be a promising natural drug, which can be used in treatment against C. albicans and S. mutans in oral diseases.

Activity of Ligustrum robustum (Roxb.) Blume extract against the biofilm formation and exopolysaccharide synthesis of Streptococcus mutans

Ligustrum robustum (Roxb.) Blume is utilized as a traditional Chinese herbal tea with various health benefits and protective effects. Streptococcus mutans is an important cariogenic oral bacteria species. The present study aimed to assess the influence of Ligustrum robustum extract (LRE) on the biofilm formation of S. mutans and the mechanism of its action, as well as to identify its chemical components. For chemical identification, HPLC-MS and nuclear magnetic resonance were applied and four identified phytochemicals were reported (Ligurobustoside B, Ligurobustoside N, Ligurobustoside J, and Ligurobustoside C). The dose-dependent (0.5 to 2.0 μg/μL) antimicrobial toxicity of LRE against S. mutans biofilm formation and exopolysaccharide (EPS) synthesis was evaluated by confocal laser scanning microscopy (CLSM), Crystal violet stain, and CFU counting. The microstructure of S. mutans biofilm treated with LRE was investigated both on glass coverslips and ex vivo bovine dental enamel by scanning electron microscopy (SEM). Moreover, LRE downregulated the expression of S. mutans glucosyltransferase-encoding genes gtfB, gtfC, and gtfD, and the quorum sensing (QS) factors comD and comE, suggesting its toxic mechanism. In addition, the result of CCK-8 test on human oral cells revealed an acceptable biocompatibility of LRE. These findings indicated the possible application of this daily consumed herbal tea for caries prevention.

Deletion of csn2 gene affects acid tolerance and exopolysaccharide synthesis in Streptococcus mutans

Csn2 is an important protein of the CRISPR-Cas system. The physiological function of this protein and its regulatory role in Streptococcus mutans, as the primary causative agent of human dental caries, is still unclear. In this study, we investigated whether csn2 deletion would affect S. mutans physiology and virulence gene expression. We used microscopic imaging, acid killing assays, pH drop, biofilm formation, and exopolysaccharide (EPS) production tests to determine whether csn2 deletion influenced S. mutans colony morphology, acid tolerance/production, and glucan formation abilities. Comparisons were made between quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) data from the UA159 and csn2 deletion strain to determine the impact of csn2 knockout on S. mutans gene expression. The results showed that deletion of S. mutans csn2 changed its colony morphotype and made it more sensitive to acid. The expression levels of aciduricity genes, including leuA, leuB, leuC, and leuD, were significantly down-regulated. Acid adaptation restored the aciduricity of csn2 mutant and enhanced the ability to synthesize EPS. The expression levels of EPS synthesis-related genes, including gtfC and gtfD, were significantly up-regulated after acid adaptation. In summary, deletion of S. mutans csn2 exerted multiple effects on the virulence traits of this pathogen, including acid tolerance and EPS formation, and that these alterations could partially be attributed to changes in gene expression upon loss of csn2. Understanding the function of csn2 in S. mutans might lead to novel strategies to prevent or treat imbalances in oral microbiota that may favor diseases.

Antimicrobial and Antibiofilm Effect of Cranberry Extract on Streptococcus mutans and Lactobacillus acidophilus: An In Vitro Study

Background

Nature has been a source of medicinal treatments since millennia and plant-based systems continue to play an essential role.

Aim

To study the antimicrobial and antibiofilm effect of cranberry on Streptococcus mutans and Lactobacillus acidophilus.

Materials and methods

The ethanolic extract of cranberry was tested against standard MTCC strains of S. mutans (MTCC 25175) and L. acidophilus (MTCC 8129) for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The time kill assay was performed to check the time-dependent bactericidal effect of the cranberry extract on microorganisms. Percentage of cell adhesion and biofilm inhibition of the dental microorganism at various doses of cranberry extract was measured by a spectrophotometer and biofilm morphology characteristics were observed under scanning electron microscopy. All the tests were carried out in triplicates. Data were computed in the SPSS software and mean/SD was determined. The results are presented in a descriptive manner; Kruskal–Wallis analysis of variance (ANOVA) and the Friedman's test were applied for comparative evaluation of the groups. p value <0.05 was considered statistically significant.

Results

The results showed that MICs of cranberry extract against S. mutans and L. acidophilus are 12.5 mg/dL and 6.125 mg/dL, respectively, and MBCs are 25 mg/dL and 12.5 mg/dL, respectively. A significant decrease in the biofilm formation and cell adhesion of microorganisms at MIC (50%) and MBC (70%) was observed as compared to control as observed under a spectrophotometer and a scanning electron microscope.

Conclusion

This study has identified bactericidal, bacteriostatic, and antibiofilm effects of cranberry extract against S. mutans and L. acidophilus in a time-dependent and dose-dependent manner.

How to cite this article

Singhal R, Patil P, Siddibhavi M, et al. Antimicrobial and Antibiofilm Effect of Cranberry Extract on Streptococcus mutans and Lactobacillus acidophilus: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(1):11–15.

Antimicrobial Effect of a Peptide Containing Novel Oral Spray on Streptococcus mutans

Objective

To investigate the antibacterial effect of a novel antimicrobial peptide containing oral spray GERM CLEAN on Streptococcus mutans (S. mutans) in vitro and further explore the related mechanisms at phenotypic and transcriptional levels.

Methods

The disk diffusion method was used to preliminarily appraise the antimicrobial effect of GERM CLEAN. The minimal inhibitory concentration (MIC) of GREM CLEAN towards S. mutans was determined by the broth dilution method. S. mutans was determined by the broth dilution method.

Results

The diameter (10.18 ± 1.744 mm) of inhibition zones formed by GERM CLEAN preliminarily indicated its inhibitory effect on the major cariogenic bacteria S. mutans was determined by the broth dilution method. S. mutans was determined by the broth dilution method. S. mutans was determined by the broth dilution method. S. mutans was determined by the broth dilution method. gtfB, gtfC, gtfD, and ldh were significantly repressed by treating with GERM CLEAN, and this was consistent with our phenotypic results.

Conclusion

The novel antimicrobial peptide containing oral spray GERM CLEAN has an anti-Streptococcus mutans effect and the inhibitory property may be due to suppression of the virulence factors of S. mutans including adhesive, acidogenicity, EPS, and biofilm formation.Streptococcus mutans effect and the inhibitory property may be due to suppression of the virulence factors of S. mutans including adhesive, acidogenicity, EPS, and biofilm formation.S. mutans was determined by the broth dilution method.

Effects of the natural compound, oxyresveratrol, on the growth of Streptococcus mutans, and on biofilm formation, acid production, and virulence gene expression

Streptococcus mutans is one of the major pathogens of dental caries. Oxyresveratrol, a natural compound found in plants, exerts inhibitory effects on many bacterial species but its effect on S. mutans is unknown. The objective of this study was to clarify the antibacterial effect of oxyresveratrol on S. mutans, including effects on basic viability, acidogenicity, acidurity, and extracellular polysaccharide synthesis. The expression of nine genes that encode virulence and protective factors in S. mutans was measured by qRT-PCR. Oxyresveratrol showed a dose-dependent inhibitory effect on survival of S. mutans. At 250 μg ml^-1 , oxyresveratrol reduced the S. mutans survival rate, inhibited synthesis of water-insoluble glucans, compromised biofilm formation, and significantly down-regulated the expression of glucosyltransferase-I (gtfB) and glucosyltransferase-SI (gtfC). However, the enzymatic activity of lactate dehydrogenase protein was increased and the expression of lactate dehydrogenase (ldh) and ATP synthase subunit beta (atpD) genes were also up-regulated. Besides, glucosyltransferase S (gtfD) up-regulation indicated that water-soluble glucan synthesis was promoted. The vicR, liaR, and comDE genes, which exert a self-protective function in response to external stress, were also up-regulated. In conclusion, oxyresveratrol inhibited the growth of S. mutans and also reduced biofilm formation, acid production, and synthesis of water-insoluble glucans by this organism. In addition, oxyresveratrol also activated a series of S. mutans self-protection mechanisms.

The effect of smoking on caries-related microorganisms

INTRODUCTION

Epidemiological studies have shown a close relationship between smoking and dental caries. Bacteria are one of the essential factors of caries formation. The imbalance of cariogenic bacteria and commensal bacteria in dental plaque results in higher production of acid that can corrode dental hard tissue. The aim of our review is to summarize the effect of smoking on caries-related bacteria.

METHODS

English articles available in Pubmed and ScienceDirect databases and published before December 2018 were searched. A variety of evidence was collected including not only the influence of cigarette products on bacteria strains in vitro but also their effect on bacterial composition in saliva and dental plaque in vivo. We particularly emphasize the mechanisms by which nicotine acts on oral bacteria.

RESULTS

The components of cigarettes promote the growth of cariogenic microorganisms. The mechanisms of how nicotine enhances Streptococcus mutans, Lactobacilli, Streptococcus gordonii, Actinomyces and Candida albicans are described separately in detail. The commensal bacteria, Streptococcus sanguinis, show less competitive capability in the presence of nicotine. Smoking influences saliva by lowering the buffer capability, altering its chemical agent and bacterial components, and therefore promotes the formation of a caries-susceptible environment.

CONCLUSIONS

Cigarette smoking and nicotine exposure promote the cariogenic activity of oral microorganisms and the formation of a caries-susceptible environment. This suggests that smokers should quit smoking, amongst other health reasons, also for their oral health.

Deletion of cas3 gene in Streptococcus mutans affects biofilm formation and increases fluoride sensitivity

OBJECTIVE

The goal of this study was to analyze the impact of cas3 gene on the biofilm formation and virulence gene expression in S. mutans, since our previous studies have found a connection between CRISPR/Cas systems and biofilm formation in S. mutans.

METHODS

The cas3 gene in-frame deletion strains of S. mutans UA159 was constructed by a two-step transformation procedure and the cas3 mutant strain was complemented in trans. The biofilm biomass was measured by crystal violet staining, and the synthesis of exopolysaccharides (EPS) was measured by the anthrone-sulfuric method. Biofilm analysis and structural imaging was using confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) assays. The fluorescence in situ hybridization (FISH) was used to analyze the spatiotemporal interactions between S. mutans and Streptococcus sanguinis. Fluoride sensitivity was determined using fluoride tolerance assays. The expression of biofilm formation related genes was evaluated by qRT-PCR.

RESULTS

Our results showed that S. mutans cas3 deletion strain formed less biofilm and became less competitive when it was co-cultured with S. sanguinis under fluoride treatment. The expression levels of virulence genes including vicR, gtfC, smu0630 and comDE were significantly downregulated.

CONCLUSIONS

The cas3 gene in S. mutans could regulate biofilm formation and fluoride resistance, consequently affecting S. mutans competitiveness in a dual-species biofilm model under fluoride treatment. These results also provide a potential strategy for enhancing fluoride specificity, with cas3 gene as a potential genetic target in the modulation of oral microecology and the treatment of dental caries.

A GntR Family Transcription Factor in Streptococcus mutans Regulates Biofilm Formation and Expression of Multiple Sugar Transporter Genes

GntR family transcription factors have been implicated in the regulation of carbohydrate transport and metabolism in many bacteria. However, the function of this transcription factor family is poorly studied in Streptococcus mutans, which is a commensal bacterium in the human oral cavity and a well-known cariogenic pathogen. One of the most important virulence traits of S. mutans is its ability to transport and metabolize carbohydrates. In this study, we identified a GntR transcription factor in S. mutans named StsR (Sugar Transporter Systems Regulator). The deletion of the stsR gene in S. mutans caused a decrease in both the formation of biofilm and the production of extracellular polysaccharides (EPS) at early stage. Global gene expression profiling revealed that the expression levels of 188 genes were changed in the stsR mutant, which could be clustered with the sugar PTS and ABC transporters. Furthermore, StsR protein was purified and its conserved DNA binding motif was determined using electrophoretic mobility shift assays (EMSA) and DNase I footprinting assays. Collectively, the results of this research indicate that StsR is an important transcription factor in S. mutans that regulates the expression of sugar transporter genes, production of EPS and formation of biofilm.

Effects of Antimicrobial Peptide GH12 on the Cariogenic Properties and Composition of a Cariogenic Multispecies Biofilm

Dental caries is a biofilm-mediated disease that occurs when acidogenic/aciduric bacteria obtain an ecological advantage over commensal species. In previous studies, the effects of the antimicrobial peptide GH12 on planktonic bacteria and monospecies biofilms were confirmed. The objectives of this study were to investigate the effects of GH12 on a cariogenic multispecies biofilm and to preliminarily explain the mechanism. In this biofilm model, Streptococcus mutans ATCC 70061 was the representative of cariogenic bacteria, while Streptococcus gordonii ATCC 35105 and Streptococcus sanguinis JCM 5708 were selected as healthy microbiota. The results showed that GH12 was more effective in suppressing S. mutans than the other two species, with lower MIC and minimal bactericidal concentration (MBC) values among diverse type strains and clinical isolated strains. Therefore, GH12, at no more than 8 mg/liter, was used to selectively suppress S. mutans in the multispecies biofilm. GH12 at 4 mg/liter and 8 mg/liter reduced the cariogenic properties of the multispecies biofilm in biofilm formation, glucan synthesis, and lactic acid production. In addition, GH12 suppressed S. mutans within the multispecies biofilm and changed the bacterial composition. Furthermore, 8 mg/liter GH12 showed a selective bactericidal impact on S. mutans, and GH12 promoted hydrogen peroxide production in S. sanguinis and S. gordonii, which improved their ecological advantages. In conclusion, GH12 inhibited the cariogenic properties and changed the composition of the multispecies biofilm through a two-part mechanism by which GH12 directly suppressed the growth of S. mutans as well as enhanced the ecological competitiveness of S. sanguinis and S. gordonii IMPORTANCE Dental caries is one of the most prevalent chronic infectious diseases worldwide, with substantial economic and quality-of-life impacts. Streptococcus mutans has been considered the principal pathogen of dental caries. To combat dental caries, an antimicrobial peptide, GH12, was designed, and its antibacterial effects on planktonic S. mutans and the monospecies biofilm were confirmed. As etiological concepts of dental caries evolved to include microecosystems, the homeostasis between pathogenic and commensal bacteria and a selective action on cariogenic virulence have increasingly become the focus. The novelty of this research was to study the effects of the antimicrobial peptides on a controlled cariogenic multispecies biofilm model. Notably, the role of an antimicrobial agent in regulating interspecific competition and composition shifts within this multispecies biofilm was investigated. With promising antibacterial and antibiofilm properties, the use of GH12 might be of importance in preventing and controlling caries and other dental infections.

Function of alanine racemase in the physiological activity and cariogenicity of Streptococcus mutans

The enzyme alanine racemase (Alr) has been a new target for the development of antibacterial drugs based on the involvement of D-Ala in bacterial cell wall biosynthesis. Our previous study noted that Alr is essential for the growth and interspecies competitiveness of S. mutans, the major causative organism of dental caries. However, physiological activity and cariogenicity of S. mutans affected by Alr remains unknown. The current study examined the biofilm biomass, biofilm structure, extracellular polysaccharide (EPS) synthesis, glucosyltransferase (gtf) gene expression, acid production and acid tolerance in the alr-mutant strain. We found that biofilm formation, biofilm structure, and EPS synthesis was in a D-Ala dose-dependent manner. Biofilm structure was loose in alr-mutant group and the ratio of EPS/bacteria was also elevated. Additionally, the expression levels of multiple gtfs were up-regulated, and acid tolerance was decreased. We also established in vivo models of dental caries and found that the incidence and severity of the caries were decreased in the alr-mutant group in comparison to the parental S. mutans group. Our in vivo and in vitro experiments demonstrate that Alr is essential for the cariogenicity of S. mutans and that Alr might be a potential target for the prevention and treatment of caries.

In silico identification of potential inhibitors targeting Streptococcus mutans sortase A

Dental caries is one of the most common chronic diseases and is caused by acid fermentation of bacteria adhered to the teeth. Streptococcus mutans (S. mutans) utilizes sortase A (SrtA) to anchor surface proteins to the cell wall and forms a biofilm to facilitate its adhesion to the tooth surface. Some plant natural products, especially several flavonoids, are effective inhibitors of SrtA. However, given the limited number of inhibitors and the development of drug resistance, the discovery of new inhibitors is urgent. Here, the high-throughput virtual screening approach was performed to identify new potential inhibitors of S. mutans SrtA. Two libraries were used for screening, and nine compounds that had the lowest scores were chosen for further molecular dynamics simulation, binding free energy analysis and absorption, distribution, metabolism, excretion and toxicity (ADMET) properties analysis. The results revealed that several similar compounds composed of benzofuran, thiadiazole and pyrrole, which exhibited good affinities and appropriate pharmacokinetic parameters, were potential inhibitors to impede the catalysis of SrtA. In addition, the carbonyl of these compounds can have a key role in the inhibition mechanism. These findings can provide a new strategy for microbial infection disease therapy.

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

Cariogenic virulence factors of Streptococcus mutans include acidogenicity, aciduricity, and extracellular polysaccharides (EPS) synthesis. The de novo designed antimicrobial peptide GH12 has shown bactericidal effects on S. mutans, but its interaction with virulence and regulatory systems of S. mutans remains to be elucidated. The objectives were to investigate the effects of GH12 on virulence factors of S. mutans, and further explore the function mechanisms at enzymatic and transcriptional levels. To avoid decrease in bacterial viability, we limited GH12 to subinhibitory levels. We evaluated effects of GH12 on acidogenicity of S. mutans by pH drop, lactic acid measurement and lactate dehydrogenase (LDH) assay, on aciduricity through survival rate at pH 5.0 and F₁F₀-ATPase assay, and on EPS synthesis using quantitative measurement, morphology observation, vertical distribution analyses and biomass calculation. Afterwards, we conducted quantitative real-time PCR to acquire the expression profile of related genes. GH12 at 1/2 MIC (4 mg/L) inhibited acid production, survival rate, EPS synthesis, and biofilm formation. The enzymatic activity of LDH and F₁F₀-ATPase was inhibited, and ldh, gtfBCD, vicR, liaR, and comDE genes were significantly downregulated. In conclusion, GH12 inhibited virulence factors of S. mutans, through reducing the activity of related enzymes, downregulating virulence genes, and inactivating specific regulatory systems.

Association between secondhand smoke exposure and early eruption of deciduous teeth: a cross-sectional study

INTRODUCTION

Secondhand smoke (SHS) exposure is a risk factor for early childhood caries. Here we examined the association between SHS exposure and early tooth eruption (ETE) to clarify the additional etiology of an increased chance of contact between the tooth’s surface and acid produced by fermenting oral bacteria.

METHODS

Data of 388 child–mother pairs who attended health checkups at public health centers were assessed for children aged ≥18 months. SHS exposure was reported as maternal smoking during pregnancy and household smoking after birth. Associations between SHS exposure and ETE (≥3 canines in the oral cavity) were tested using multivariable analyses of the dose-response relationship. Subgroup and sensitivity analyses were performed for birth-weight subgroups and SHS exposure variables, respectively.

RESULTS

ETE prevalence was 65.5%, 68.1%, and 76.9% in the no, medium-dose (ceased partway and sometimes), and highest-dose (every day) exposure groups, respectively, during pregnancy, and 61.5%, 75.0%, and 75.5%, respectively, after birth. The association between the highest dose exposure during pregnancy and ETE was not significant (OR=1.42, 95% CI: 0.34–5.96, p=0.631), whereas that between highest dose exposure after birth and ETE was significant (OR=2.13, 95% CI: 1.06–4.31, p=0.034); this association was distinct in the subgroup of children with smaller birth weights (<3000 g) (OR=3.19, 95% CI: 1.08–9.44, p=0.036). The dose-response relationship was consistently significant for exposure after birth (p<0.05). The sensitivity analysis that employed no SHS exposure, as a reference, revealed that exposure after birth but no exposure during pregnancy was significantly associated with ETE (OR=2.29, 95% CI: 1.19–4.40, p=0.013). However, the association between exposure during pregnancy and ETE was consistently non-significant (p>0.05).

CONCLUSIONS

When controlling for variables of birth weight and exposure type, SHS exposure after birth was independently associated with the early eruption of deciduous canines. Further studies are warranted to examine the trajectory of SHS exposure after birth, ETE, and early childhood caries incidence.

ABBREVIATIONS

ETE: Early tooth eruption, SHS: Secondhand smoke

Nicotine is a risk factor for dental caries: An in vivo study

Background/purpose

Streptococcus mutans is an important pathogen in the development of dental caries. Many studies have focused on the relationship between nicotine and S. mutans in vitro. The aim of this study was to investigate the effect of nicotine on the growth of S. mutans and its cariogenic potential in vivo.

Materials and methods

Sixteen male Specific-pathogen-free Wistar rats were divided into 2 groups (nicotine-treated and nicotine-untreated group) and infected with S. mutans. The S. mutans suspension was treated with 1 mg/mL nicotine in the nicotine-treated group. The Keyes method was used to evaluate sulcal caries of rats, and dental plaque on molar teeth was observed by scanning electron microscopy (SEM).

Results

Incidence of sulcal caries was higher in nicotine-treated group compared to nicotine-untreated group (42.7 ± 1.7 vs 37.3 ± 4.9, P = 0.009). Severity of caries increased with nicotine treatment. The slightly dentinal caries scores and moderate dentinal caries scores were higher in the presence of nicotine (P < 0.001). Increased number of S. mutans cells attached to dental surface was observed under SEM in the nicotine-treated group.

Conclusion

Nicotine would promote the attachment of S. mutans to dental surface, and further increase the incidence and severity of dental caries. Therefore, nicotine might be a risk factor for smoking-induced caries.

[Construction of srtA-deletion mutant of Streptococcus mutans by an in-frame deletion system]

OBJECTIVE

To construct srtA-gene deletion mutant of Streptococcus mutans (S. mutans) UA159 with IFDC2 cassette through overlapping polymerase chain reaction (PCR) and allelic homologous recombination.

METHODS

First, the upstream and downstream fragments surrounding the srtA and IFDC2 cassette were PCR amplified and ligated through overlapping PCR. The resulting amplicon was transformed into UA159, and positive transformants were selected on BHI plates containing erythromycin. Second, upstream and downstream fragments of srtA with overlap regions were generated by PCR and were overlapped to create upΔ-down amplicon. Then, the upΔ-down amplicon was transformed into the aforementioned positive transformants and selected on BHI plates containing p-Cl-Phe.

RESULTS

The PCR analysis and DNA sequencing results indicated that the coding region of the srtA was completely deleted, and the upstream and downstream regions flanking the srtA were ligated seamlessly.

CONCLUSIONS

The markerless srtA-deletion mutant of S. mutans was constructed successfully, which laid a foundation for further study of its biological function and influence on the biofilm formation of S. mutans.

Characterization of the clustered regularly interspaced short palindromic repeats sites in Streptococcus mutans isolated from early childhood caries patients

OBJECTIVE

The aim of this study was to analyze the characteristics of the clustered regularly interspaced short palindromic repeats (CRISPR) sites in 45 clinical Streptococcus mutans strains and their relationship to the clinical manifestations of early childhood caries (ECC).

METHODS

Forty-five S. mutans strains were isolated from the plaque samples taken from sixty-three children. CRISPR sites were sequenced and BLAST was used to compare these sites to those in the CRISPRTarget database. The association between the distribution of CRISPR sites and the manifestation of caries was analyzed by Chi-Square test. Further, biofilm formation (by crystal violet staining) and the synthesis of polysaccharide (by anthrone-sulfuric method) of all clinical isolated S. mutans strains with both CRISPR sites and no CRISPR site were comapared. Finally, acidogenicity and acidurity of two typical strains were determined using pH drop and acid tolerance assays. Biofilm formation and EPS synthesis by two typical strains were compared by 3D CLSM (Confocal Laser Scanning Microscope) assays and the expression of gtf genes were evaluated using qPCR.

RESULTS

We found that most of the spacers in the clinical S. mutans strains were derived from Streptococcus phages APCM01 and M102. The number of CRISPR sites in these strains was associated with the clinical manifestations of ECC. Moreover, we found that the biofilm formation and EPS synthesis ability of the S. mutans strains with both CRISPR sites was significant improved.

CONCLUSIONS

An association was found between the distribution of CRISPR sites and the clinical manifestations of caries. The CRISPR sites might contribute to the cariogenic potential of S. mutans.

Effects of diadenylate cyclase deficiency on synthesis of extracellular polysaccharide matrix of Streptococcus mutans revisit

An emerging secondary messenger c-di-AMP plays an important role in bacterial physiology. It was reported by Cheng et al. that inactivation of a gene coding for diadenylate cyclase (DAC), a c-di-AMP producing enzyme, resulted in enhanced synthesis of extracellular polysaccharides (EPS) by a cariogenic bacterium, Streptococcus mutans (Cheng et al., 2016). We constructed a similar mutant and observed a completely different effect, the DAC deficiency resulted in a decrease in the production of EPS. Our studies provided the following compelling evidence, (1) the DAC mutant we constructed can be readily complemented for the production of EPS, while the mutant from the Cheng group cannot; (2) Our mutant exhibits the regular pattern of key enzymes that produce EPS, glucosyltransferases (Gtfs), while Cheng et al. reported an irregular pattern, which was inconsistent with their earlier studies. (3) We demonstrated that the response of the DAC mutant to oxidative stress is independent of GtfB, the key enzyme producing EPS, while the Cheng report suggests that overproduction of EPS is a responsive mechanism for the DAC mutant to adapt to the oxidative stress. Therefore, the validity of the relationship between DAC and EPS reported by Cheng et al. warrants further investigation and clarification.

Quantitative analysis of S. mutans, Lactobacillus and Bifidobacterium found in initial and mature plaques in Thai children with early childhood caries

AIMS

To quantify Streptococcus mutans, lactobacillus and bifidobacterium in initial and mature plaque collected from children with severe early childhood caries (S-ECC) and caries-free (CF) groups and to analyse the association between these bacteria and caries-related factors in each group.

STUDY DESIGN

A collection of 120 initial and overnight supra-gingival plaques were collected from Thai children aged 2-5 years-old (S-ECC = 60, CF = 60). Plaque, gingival indices and decayed, missing, filled tooth (dmft) scores were recorded. A questionnaire was used to assess the parents' attitudes and behaviour regarding the child's oral hygiene care and diet.

METHODS

After DNA extraction, quantitative real-time polymerase chain reaction (PCR) using fluorescent dye (SYBR green) was performed.

RESULTS

Levels of Streptococcus mutans, lactobacillus and bifidobacterium in both initial and mature plaques of S-ECC were significantly higher than those from the caries-free group (p < 0.05). The ratio of S. mutans, lactobacillus, and bifidobacterium to the total bacteria in S-ECC was significantly higher than in the caries-free group (p < 0.05). Levels of lactobacillus and bifidobacterium in both plaques significantly correlated with dmft scores and the plaque index, while S. mutans levels only correlated with dmft scores (p < 0.05). Factors that were significantly associated with caries were parents's education, duration of bottle feeding, especially during sleeping and the frequency of consuming cariogenic food between meals (p < 0.05).

CONCLUSION

Levels of S. mutans, lactobacillus, bifidobacterium and the ratio of these bacteria to total bacteria in both initial and mature plaques were significantly higher in children with S-ECC and related to dmft scores, oral hygiene and dietary habits.

Nicotine Enhances Interspecies Relationship between Streptococcus mutans and Candida albicans

Streptococcus mutans and Candida albicans are common microorganisms in the human oral cavity. The synergistic relationship between these two species has been deeply explored in many studies. In the present study, the effect of alkaloid nicotine on the interspecies between S. mutans and C. albicans is explored. We developed a dual-species biofilm model and studied biofilm biomass, biofilm structure, synthesis of extracellular polysaccharides (EPS), and expression of glucosyltransferases (Gtfs). Biofilm formation and bacterial and fungal cell numbers in dual-species biofilms increased in the presence of nicotine. More C. albicans cells were present in the dual-species biofilms in the nicotine-treated groups as determined by scanning electron microscopy. The synthesis of EPS was increased by 1 mg/ml of nicotine as detected by confocal laser scanning microscopy. The result of qRT-PCR showed gtfs expression was upregulated when 1 mg/ml of nicotine was used. We speculate that nicotine promoted the growth of S. mutans, and more S. mutans cells attracted more C. albicans cells due to the interaction between two species. Since S. mutans and C. albicans are putative pathogens for dental caries, the enhancement of the synergistic relationship by nicotine may contribute to caries development in smokers.

Clotrimazole and econazole inhibit Streptococcus mutans biofilm and virulence in vitro

OBJECTIVE

The aim of this study was to determine the inhibitory effect of eight antifungal drugs on S. mutans growth, biofilm formation and virulence factors.

METHODS

The actions of antifungal drugs on S. mutans were determined by recovery plates and survival kinetic curves. Biofilms were observed by scanning electron microscopy and the viable cells were recovered on BHI plates, meanwhile biofilms were stained by BacLight live/dead kit to investigate the biofilm viability. Bacteria/extracellular polysaccharides staining assays were performed to determine the EPS production of S. mutans biofilms. Acidogenicity and acidurity of S. mutans were determined using pH drop and acid tolerance assays, and the expression of ldh gene was evaluated using qPCR.

RESULTS

We found that clotrimazole (CTR) and econazole (ECO) showed antibacterial activities on S. mutans UA159 and S. mutans clinical isolates at 12.5 and 25mg/L, respectively. CTR and ECO could also inhibit S. mutans biofilm formation and reduce the viability of preformed biofilm. CTR and ECO affected the live/dead ratio and the EPS/bacteria ratio of S. mutans biofilms. CTR and ECO also inhibited the pH drop, lactate acid production, and acid tolerance. The abilities of CTR and ECO to inhibit S. mutans ldh expression were also confirmed.

CONCLUSIONS

We found that two antifungal azoles, CTR and ECO, had the abilities to inhibit the growth and biofilm formation of S. mutans and more importantly, they could also inhibit the virulence factors of S. mutans.

Effect of nicotine on cariogenic virulence of Streptococcus mutans

Nicotine has well-documented effects on the growth and colonization of Streptococcus mutans. This study attempts to investigate the effects of nicotine on pathogenic factors of S. mutans, such as the effect on biofilm formation and viability, expression of pathogenic genes, and metabolites of S. mutans. The results demonstrated that addition of nicotine did not significantly influence the viability of S. mutans cells. The biofilms became increasingly compact as the concentrations of nicotine increased. The expression of virulence genes, such as ldh and phosphotransferase system (PTS)-associated genes, was upregulated, and nlmC was upregulated significantly, while ftf was downregulated. The lactate concentration of S. mutans grown in 1 mg/mL of nicotine was increased up to twofold over either biofilm or planktonic cells grown without nicotine. Changes in the metabolites involved in central carbon metabolism from sucrose indicated that most selected metabolites were detectable and influenced by increased concentrations of nicotine. This study demonstrated that nicotine can influence the pathogenicity of S. mutans and may lead to increased dental caries through the production of more lactate and the upregulation of virulence genes.

The spherical nanoparticle-encapsulated chlorhexidine enhances anti-biofilm efficiency through an effective releasing mode and close microbial interactions

We reported two forms (sphere and wire) of newly fabricated chlorhexidine (CHX)-loaded mesoporous silica nanoparticles (MSNs), and investigated their releasing capacities and anti-biofilm efficiencies. The interactions of the blank MSNs with planktonic oral microorganisms were assessed by field emission scanning electron microscopy. The anti-biofilm effects of the two forms of nanoparticle-encapsulated CHX were examined by 2,3-bis (2-methoxy- 4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide. The profiles of biofilm penetration were analyzed by fluorescent-labeled MSNs using confocal microscopy and ImageJ. The spherical MSNs with an average diameter of 265 nm exhibited a larger surface area and faster CHX-releasing rate than the MSN wires. The field emission scanning electron microscopy images showed that both shaped MSNs enabled to attach and further fuse with the surfaces of testing microbes. Meanwhile, the nanoparticle-encapsulated CHX could enhance the anti-biofilm efficiency with reference to its free form. Notably, the spherical nanoparticle-encapsulated CHX presented with a greater anti-biofilm capacity than the wire nanoparticle-encapsulated CHX, partly due to their difference in physical property. Furthermore, the relatively even distribution and homogeneous dispersion of spherical MSNs observed in confocal images may account for the enhanced penetration of spherical nanoparticle-encapsulated CHX into the microbial biofilms and resultant anti-biofilm effects. These findings reveal that the spherical nanoparticle-encapsulated CHX could preferably enhance its anti-biofilm efficiency through an effective releasing mode and close interactions with microbes.

Effect of LongZhang Gargle on Biofilm Formation and Acidogenicity of Streptococcus mutans In Vitro

Streptococcus mutans, with the ability of high-rate acid production and strong biofilm formation, is considered the predominant bacterial species in the pathogenesis of human dental caries. Natural products which may be bioactive against S. mutans have become a hot spot to researches to control dental caries. LongZhang Gargle, completely made from Chinese herbs, was investigated for its effects on acid production and biofilm formation by S. mutans in this study. The results showed an antimicrobial activity of LongZhang Gargle against S. mutans planktonic growth at the minimum inhibitory concentration (MIC) of 16% and minimum bactericidal concentration (MBC) of 32%. Acid production was significantly inhibited at sub-MIC concentrations. Biofilm formation was also significantly disrupted, and 8% was the minimum concentration that resulted in at least 50% inhibition of biofilm formation (MBIC50). A scanning electron microscopy (SEM) showed an effective disruption of LongZhang Gargle on S. mutans biofilm integrity. In addition, a confocal laser scanning microscopy (CLSM) suggested that the extracellular polysaccharides (EPS) synthesis could be inhibited by LongZhang Gargle at a relatively low concentration. These findings suggest that LongZhang Gargle may be a promising natural anticariogenic agent in that it suppresses planktonic growth, acid production, and biofilm formation against S. mutans.

Chinese herb medicine against Sortase A catalyzed transformations, a key role in gram-positive bacterial infection progress

Many Gram-positive bacteria can anchor their surface proteins to the cell wall peptidoglycan covalently by a common mechanism with Sortase A (SrtA), thus escaping from the host's identification of immune cells. SrtA can complete this anchoring process by cleaving LPXTG motif conserved among these surface proteins and thus these proteins anchor on the cell wall. Moreover, those SrtA mutants lose this capability to anchor these relative proteins, with these bacteria no longer infectious. Therefore, SrtA inhibitors can be promising anti-infective agents to cure bacterial infections. Chinese herb medicines (CHMs) (chosen from Science Citation Index) have exhibited inhibition on SrtA of Gram-positive pathogens irreversibly or reversibly. In general, CHMs are likely to have important long-term impact as new antibacterial compounds and sought after by academia and the pharmaceutical industry. This review mainly focuses on SrtA inhibitors from CHMs and the potential inhibiting mechanism related to chemical structures of compounds in CHMs.

Cyclic di-AMP mediates biofilm formation

Cyclic di-AMP (c-di-AMP) is an emerging second messenger in bacteria. It has been shown to play important roles in bacterial fitness and virulence. However, transduction of c-di-AMP signaling in bacteria and the role of c-di-AMP in biofilm formation are not well understood. The level of c-di-AMP is modulated by activity of di-adenylyl cyclase that produces c-di-AMP and phosphodiesterase (PDE) that degrades c-di-AMP. In this study, we determined that increased c-di-AMP levels by deletion of the pdeA gene coding for a PDE promoted biofilm formation in Streptococcus mutans. Deletion of pdeA upregulated expression of gtfB, the gene coding for a major glucan producing enzyme. Inactivation of gtfB blocked the increased biofilm by the pdeA mutant. Two c-di-AMP binding proteins including CabPA (SMU_1562) and CabPB (SMU_1708) were identified. Interestingly, only CabPA deficiency inhibited both the increased biofilm formation and the upregulated expression of GtfB observed in the pdeA mutant. In addition, CabPA but not CabPB interacted with VicR, a known transcriptional factor that regulates expression of gtfB, suggesting that a signaling link between CabPA and GtfB through VicR. Increased biofilm by the pdeA deficiency also enhanced bacterial colonization of Drosophila in vivo. Taken together, our studies reveal a new role of c-di-AMP in mediating biofilm formation through a CabPA/VicR/GtfB signaling network in S. mutans.

Regulation of oxidative response and extracellular polysaccharide synthesis by a diadenylate cyclase in Streptococcus mutans

Cyclic diadenosine monophosphate (c-di-AMP) has been implicated in the control of many important bacterial activities. However, the function of this molecule in Streptococcus mutans, the primary aetiological agent of human dental caries, is unknown. In this study, we identified and characterized a diadenylate cyclase, named CdaA, in S. mutans. Furthermore, we showed that in-frame deletion of the cdaA gene in S. mutans causes decreased c-di-AMP levels, increased sensitivity to hydrogen peroxide and increased production of extracellular polysaccharides. Global gene expression profiling revealed that more than 200 genes were significantly upregulated or downregulated (> 2.0-fold) in the cdaA mutant. Interestingly, genes with increased or decreased expression were clustered in cellular polysaccharide biosynthetic processes and oxidoreductase activity respectively. Notably, the expression of several genomic islands, such as GTF-B/C, TnSmu, CRISPR1-Cas and CRISPR2-Cas, was found to be altered in the cdaA mutant, indicating a possible link between these genomic islands and c-di-AMP signalling. Collectively, the results reported here show that CdaA is an important global modulator in S. mutans and is required for optimal growth and environmental adaption. This report also paves the way to unveil further the roles of c-di-AMP signalling networks in the biology and pathogenicity of S. mutans.

d-Alanine metabolism is essential for growth and biofilm formation of Streptococcus mutans

Part of the d-alanine (d-Ala) metabolic pathway in bacteria involves the conversion of l-alanine to d-Ala by alanine racemase and the formation of d-alanyl-d-alanine by d-alanine-d-alanine ligase, the product of which is involved in cell wall peptidoglycan synthesis. At present, drugs that target the metabolic pathway of d-Ala are already in clinical use - e.g. d-cycloserine (DCS) is used as an antibiotic against Mycobacterium tuberculosis. Streptococcus mutans is the main cariogenic bacterium in the oral cavity. Its d-Ala metabolism-associated enzymes alanine racemase and d-alanine-d-alanine ligase are encoded by the genes smu.1834 and smu.599, respectively, which may be potential targets for inhibitors. In this study, the addition of DCS blocked the d-Ala metabolic pathway in S. mutans, leading to bacterial cell wall defects, significant inhibition of bacterial growth and biofilm formation, and reductions in extracellular polysaccharide production and bacterial adhesion. However, the exogenous addition of d-Ala could reverse the inhibitory effect of DCS. Through the means of drug regulation, our study demonstrated, for the first time, the importance of d-Ala metabolism in the survival and biofilm formation of S. mutans. If the growth of S. mutans can be specifically inhibited by designing drugs that target d-Ala metabolism, then this may serve as a potential new treatment for dental caries.

Kaffir lime leaves extract inhibits biofilm formation by Streptococcus mutans

OBJECTIVES

Although kaffir lime has been reported to exhibit antioxidant and antileukemic activity, little is known about the antimicrobial effect of kaffir lime extract. Because Streptococcus mutans has been known to cause biofilm formation, it has been considered the most important causative pathogen of dental caries. Thus, the effective control of its effects on the oral biofilm is the key to the prevention of dental caries. The aims of the present study were to investigate the effect of kaffir lime leaves extract on biofilm formation and its antibacterial activity on S. mutans.

METHODS

We examined the effect of kaffir lime leaves extract on growth and biofilm formation of S. mutans. For the investigation we used a kaffir lime extract with high phenolic content. The minimum inhibitory concentration of the extract was determined by broth microdilution assay. The inhibitory effect of the test substances on biofilm formation was also investigated by biofilm formation assay and qRT-PCR of biofilm formation-associated genes.

RESULTS

Kaffir lime leaves extract inhibits the growth of S. mutans, corresponding to the activity of an antibiotic, ampicillin. Formation of biofilm by S. mutans was also inhibited by the extract. These results were confirmed by the down-regulation of genes associated with the biofilm formation.

CONCLUSIONS

The findings highlight the ability of kaffir lime leaves extract to inhibit S. mutans activity, which may be beneficial in the prevention of biofilm formation on dental surface, reducing dental plaque and decreasing the chance of dental carries.

Streptococcus mutans copes with heat stress by multiple transcriptional regulons modulating virulence and energy metabolism

Dental caries is closely associated with the virulence of Streptococcus mutans. The virulence expression of S. mutans is linked to its stress adaptation to the changes in the oral environment. In this work we used whole-genome microarrays to profile the dynamic transcriptomic responses of S. mutans during physiological heat stress. In addition, we evaluated the phenotypic changes, including, eDNA release, initial biofilm formation, extracellular polysaccharides generation, acid production/acid tolerance, and ATP turnover of S. mutans during heat stress. There were distinct patterns observed in the way that S. mutans responded to heat stress that included 66 transcription factors for the expression of functional genes being differentially expressed. Especially, response regulators of two component systems (TCSs), the repressors of heat shock proteins and regulators involved in sugar transporting and metabolism co-ordinated to enhance the cell’s survival and energy generation against heat stress in S. mutans.

Scratching the surface - tobacco-induced bacterial biofilms

Individual environmental factors, such as iron, temperature and oxygen, are known to have a profound effect on bacterial phenotype. Therefore, it is surprising so little known is about the influence of chemically complex cigarette smoke on bacterial physiology. Recent evidence has demonstrated that tobacco smoke and components alter the bacterial surface and promote biofilm formation in several important human pathogens, including Staphylococcus aureus, Streptococcus mutans, Klebsiella pneumonia, Porphyromonas gingivalis and Pseudomonas aeruginosa. The mechanisms underlying this phenomenon and the relevance to increased susceptibility to infectious disease in smokers and to treatment are reviewed.

Effects of Nicotine on Streptococcus gordonii Growth, Biofilm Formation, and Cell Aggregation

Streptococcus gordonii is a commensal species of human oral flora. It initiates dental biofilm formation and provides binding sites for later colonizers to attach to and generate mature biofilm. Smoking is the second highest risk factor for periodontal disease, and cigarette smoke extract has been reported to facilitate Porphyromonas gingivalis-S. gordonii dual-species biofilm formation. Our hypothesis is that nicotine, one of the most important and active components of tobacco, stimulates S. gordonii multiplication and aggregation. In the present study, S. gordonii planktonic cell growth (kinetic absorbance and CFU), biofilm formation (crystal violet stain and confocal laser scanning microscopy [CLSM]), aggregation with/without sucrose, and 11 genes that encode binding proteins or regulators of gene expression were investigated. Results demonstrated planktonic cell growth was stimulated by 1 to 4 mg/ml nicotine treatment. Biofilm formation was increased at 0.5 to 4 mg/ml nicotine. CLSM indicated bacterial cell mass was increased by 2 and 4 mg/ml nicotine, but biofilm extracellular polysaccharide was not significantly affected by nicotine. Cell aggregation was upregulated by 4, 8, and 16 mg/ml nicotine with sucrose and by 16 mg/ml nicotine without sucrose. Quantitative reverse transcriptase PCR indicated S. gordonii abpA, scaA, ccpA, and srtA were upregulated in planktonic cells by 2 mg/ml nicotine. In conclusion, nicotine stimulates S. gordonii planktonic cell growth, biofilm formation, aggregation, and gene expression of binding proteins. Those effects may promote later pathogen attachment to tooth surfaces, the accumulation of tooth calculus, and the development of periodontal disease in cigarette smokers.

Effects of simulated microgravity on Streptococcus mutans physiology and biofilm structure

Long-term spaceflights will eventually become an inevitable occurrence. Previous studies have indicated that oral infectious diseases, including dental caries, were more prevalent in astronauts due to the effect of microgravity. However, the impact of the space environment, especially the microgravity environment, on the virulence factors of Streptococcus mutans, a major caries-associated bacterium, is yet to be explored. In the present study, we investigated the impact of simulated microgravity on the physiology and biofilm structure of S. mutans. We also explored the dual-species interaction between S. mutans and Streptococcus sanguinis under a simulated microgravity condition. Results indicated that the simulated microgravity condition can enhance the acid tolerance ability, modify the biofilm architecture and extracellular polysaccharide distribution of S. mutans, and increase the proportion of S. mutans within a dual-species biofilm, probably through the regulation of various gene expressions. We hypothesize that the enhanced competitiveness of S. mutans under simulated microgravity may cause a multispecies micro-ecological imbalance, which would result in the initiation of dental caries. Our current findings are consistent with previous studies, which revealed a higher astronaut-associated incidence of caries. Further research is required to explore the detailed mechanisms.

Sortagging: a robust and efficient chemoenzymatic ligation strategy

Bioorthogonal, chemoselective ligation methods are an essential part of the tools utilized to investigate biochemical pathways. Specifically enzymatic approaches are valuable methods in this context due to the inherent specificity of the deployed enzymes and the mild conditions of the modification reactions. One of the most common strategies is based on the transpeptidation catalyzed by sortase A derived from Staphylococcus aureus. The procedure is well established and a wide variety of applications have been published to date. Here, implementations of sortase A, which range from protein labeling using fluorescence dyes and the preparation of cyclic proteins to the modification of entire cells, are summarized. Furthermore, there is a focus on the optimization approaches established to solve the drawbacks of sortase-mediated transpeptidation.

Effect of nicotine on dual-species biofilms of Streptococcus mutans and Streptococcus sanguinis

Both Streptococcus mutans and Streptococcus sanguinis are normal bacterial inhabitants of dental plaque. Streptococcus mutans is the major agent causing dental caries. It has been well documented that nicotine affects the growth of S. mutans. This study investigated the effect of nicotine on mono- and dual-species growth of S. mutans and S. sanguinis. The results indicate that nicotine has no significant effect on S. sanguinis grown in either mono- or dual-species biofilms. However, nicotine significantly increased (P < 0.05) the growth of S. mutans in dual-species biofilm formation. In addition, the CFU level of S. sanguinis was higher than S. mutans without nicotine in the culture. With the addition of nicotine, the level of S. mutans biofilm was significantly enhanced as the nicotine concentration increased over the level of S. sanguinis in dual-species biofilm, and we also got the same result from the fluorescence in situ hybridization detecting the two bacteria grown in biofilm formation. The exopolysaccharide (EPS) of S. mutans has also been increased by the increasing nicotine concentration, while the EPS of S. sanguinis was decreased or inhibited by the affected nicotine. The data further confirm that nicotine is able to enhance the growth of S. mutans.