Effects of Ag/ZnO nanocomposite at sub-minimum inhibitory concentrations on virulence factors of Streptococcus mutans

Dual-species biofilm of Streptococcus mutans and Candida albicans produces subsurface caries lesions on bovine enamel

OBJECTIVES

To develop a protocol for forming subsurface caries lesions on bovine enamel by dual-species biofilms of Streptococcus mutans and Candida albicans in vitro.

DESIGN

Biofilms were grown on bovine enamel specimens in artificial saliva (AS) for seven days. After 24 h of formation, the AS was supplemented or not with fluoride (F) using sodium fluoride (0.005 or 0.008 ppm F), and the biofilms were exposed or not to a 20 % sucrose solution (reproducing a cariogenic challenge) once/day. On the seventh day, the biofilms were harvested and had their extracellular polysaccharides (EPS) and inorganic components analyzed. The specimens were subjected to computed X-ray microtomography analysis to determine their mineral concentration. Data were compared using two-way analyses of variance, followed by Fisher's LSD or Student-Newman-Keuls tests (p < 0.05).

RESULTS

Biofilms exposed to the cariogenic challenge had significantly higher EPS concentrations than those not exposed, regardless of the presence of F. For biofilms grown with 0.008 ppm F, those exposed to the cariogenic challenge had lower F levels than those not exposed. For biofilms exposed to the cariogenic challenge, those grown with 0.008 ppm F had lower lesion depths and integrated mineral loss, and higher outer layers than those grown without F.

CONCLUSIONS

The dual biofilm model assessed was able to create subsurface caries lesions in bovine enamel in vitro, which was influenced by the presence of F in the culture medium and exposure to sucrose.

Targeting bacterial biofilm-related genes with nanoparticle-based strategies

Persistent infection caused by biofilm is an urgent in medicine that should be tackled by new alternative strategies. Low efficiency of classical treatments and antibiotic resistance are the main concerns of the persistent infection due to biofilm formation which increases the risk of morbidity and mortality. The gene expression patterns in biofilm cells differed from those in planktonic cells. One of the promising approaches against biofilms is nanoparticle (NP)-based therapy in which NPs with multiple mechanisms hinder the resistance of bacterial cells in planktonic or biofilm forms. For instance, NPs such as silver (Ag), zinc oxide (ZnO), titanium dioxide (TiO2), copper oxide (Cu), and iron oxide (Fe3O4) through the different strategies interfere with gene expression of bacteria associated with biofilm. The NPs can penetrate into the biofilm structure and affect the expression of efflux pump, quorum-sensing, and adhesion-related genes, which lead to inhibit the biofilm formation or development. Therefore, understanding and targeting of the genes and molecular basis of bacterial biofilm by NPs point to therapeutic targets that make possible control of biofilm infections. In parallel, the possible impact of NPs on the environment and their cytotoxicity should be avoided through controlled exposure and safety assessments. This study focuses on the biofilm-related genes that are potential targets for the inhibition of bacterial biofilms with highly effective NPs, especially metal or metal oxide NPs.

Systematic Review of Zinc's Benefits and Biological Effects on Oral Health

BACKGROUND

This review was based on the following question: "What is the state-of-the-art regarding the effect of zinc exposure in the oral cavity on a population of adults and children, compared to dental products containing materials other than zinc, considering in vivo (clinical trials and observational studies) and in vitro studies?" according to a PICOS strategy format. This study aims to analyze zinc application in dental materials, with different compositions and chemical formulations, considering how mechanical and biological properties may influence its clinical applicability.

METHODS

In vivo (clinical trials: controlled clinical trials (CCTs) and randomized controlled trials (RCTs); and observational studies: case control and cohort studies) trials or in vitro studies published in English or Italian during the last 10 years on children and adult patients with zinc exposure were included by three different reviewers using the MEDLINE (via PubMed), Scopus, and Web of Science electronic databases.

RESULTS

Titles and abstracts were evaluated following the eligibility criteria. The full texts of eligible studies were then reviewed against the inclusion/exclusion criteria. Scientific and technical information of the 33 included studies were collected into evidence tables, reporting data on in vivo and in vitro studies. A narrative approach was adopted.

CONCLUSIONS

Antibacterial activity was found to be the most studied property of zinc, but further investigations are needed to establish adjuvant zinc therapies in patients with oral disease.

The inhibitory effect of ovomucoid from egg white on biofilm formation by Streptococcus mutans

BACKGROUND

Streptococcus mutans, the main pathogen associated with tooth decay, forms cariogenic biofilms on tooth surfaces. Therefore, controlling oral biofilm helps prevent dental caries. Hen's egg is a nutrient-dense food, and egg white is a good source of protein. Ovomucoid is one of the major proteins in egg white, with a 28 kDa molecular weight. The present study aimed to investigate the inhibitory effects of ovomucoid on the biofilm formation of S. mutans by suppressing virulence factors, including bacterial adherence, cellular aggregation and exopolysaccharide (EPS) production.

RESULTS

Crystal violet staining showed that biofilm formation by S. mutans was inhibited by ovomucoid at 0.25-1 mg mL-1 levels. Field emission scanning electron microscopy also confirmed this inhibition. In addition, ovomucoid reduced mature biofilm, water-insoluble EPS synthesis and the metabolic activity of bacterial cells in the biofilm. The bacterial adhesion and aggregation abilities of S. mutans were also decreased in the presence of ovomucoid. Ovomucoid downregulated the expression of comDE and vicR genes involved in the two-component signal transduction system and gtfA and ftf genes involved in EPS production.

CONCLUSION

Ovomucoid has the potential for use as an anti-biofilm agent for dental caries treatment because of its inhibitory effects on the virulence factors of S. mutans. © 2023 Society of Chemical Industry.

Proteomics of Streptococcus mutans to Reveal the Antibiofilm Formation Mechanism of Ag/ZnO Nanocomposites with Light-Emitting Diode Radiation

Introduction

As a biofilm-associated disease, dental caries benefits from nanoparticle (NP)-based therapies. Streptococcus mutans (S. mutans) is a primary aetiologic agent for dental caries development. We successfully applied a synergistic therapy of Ag/ZnO nanocomposites combined with light-emitting diode (LED) radiation to inhibit S. mutans biofilms. However, the antibiofilm mechanism has not been fully elucidated, and little is known about the biofilm formation ability of bacteria that survive NP-based therapies.

Methods

This study explored the antibiofilm formation mechanism of this synergistic therapy by an integrated approach based upon proteomics.

Results

Synergistic therapy killed 99.8% of bacteria, while the biofilm formation ability of 0.2% surviving bacteria was inhibited. The proteomic responses of S. mutans to synergistic therapy were comprehensively characterized to unveil the mechanism of bacterial death and biofilm formation inhibition of the surviving bacteria. In total, 55 differentially expressed proteins (12 upregulated and 43 downregulated) were recorded. The bioinformatic analysis demonstrated that cellular integrity damage and regulated expression of structure-associated proteins were the main reasons for bacterial death. In addition, the proteomic study indicated the potential inhibition of metabolism in surviving bacteria and provided a biofilm-related network consisting of 17 differentially expressed proteins, explaining the multiantibiofilm formation actions. Finally, we reported and verified the inhibitory effects of synergistic therapy on sucrose metabolism and D-alanine metabolism, which disturbed the biofilm formation of surviving bacteria.

Conclusion

Our findings demonstrated that synergistic therapy killed most bacteria and inhibited the surviving bacteria from forming biofilms. Furthermore, the antibiofilm formation mechanism was revealed by proteomics analysis of S. mutans after synergistic therapy and subsequent metabolic studies. Our success may provide a showcase to explore the antibiofilm formation mechanism of NP-based therapies using proteomic studies.

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.

Inhibition of Streptococcus mutans, antioxidant property and cytotoxicity of novel nano-zinc oxide varnish

OBJECTIVE

Zinc is a potent antimicrobial against cariogenic bacteria and effective anti-plaque agent. The present study investigated the efficacy of zinc oxide nanoparticles (ZnO-NP) varnish to inhibit S. mutans growth, biofilm, acid production, and its antioxidant potential and cytotoxicity.

DESIGN

Green synthesized ZnO-NP were characterized using ultraviolet-visible spectroscopy, x-ray diffraction spectroscopy, and transmission electron microscopy. Secondary metabolites were assessed using fourier transform infrared spectroscopy. Anti-oxidant potential was ascertained using 2,2-diphenyl-2-picrylhydrazyl hydrate (DDPH) assay and cytotoxicity of synthesized nanoparticles was evaluated on human liver cancer (Hep G2) and human embryonic kidney 293 (HEK-293T) cell lines.

RESULTS

Synthesized ZnO-NP showed excellent antimicrobial properties against S. mutans, as the minimum inhibitory and bactericidal concentrations were 0.53 μg/mL, and 1.3 μg/mL respectively. ZnO-NP at 0.1 mg/μl concentration had the greatest zone of inhibition (24 mm), followed by 0.05 mg/μl ZnO-NP (23 mm) and 0.05 mg/μl ampicillin (21 mm). Further, 0.1 mg/μl ZnO-NP varnish inhibited 90 % of S. mutans biofilms and reduced 24 h acid production closest to that of baseline and it also exhibited antioxidant capacity in a dose dependent manner (94 % inhibition-100 μg/mL). Biocompatibility of ZnO-NP varnish was evaluated on Hep G2 and HEK-293T cell lines; and the highest concentration of 0.1 mg/μl ZnO-NP used caused very low cytotoxicity to Hep G2 cells and was non-cytotoxic to HEK-293T cells.

CONCLUSIONS

Within the limits of this study, ZnO-NP varnish was effective in inhibiting S. mutans and holds great potential as an effective anticaries agent.