The Inhibitory Effects of Ficin on Streptococcus mutans Biofilm Formation

Fluoride-resistant Streptococcus mutans within cross-kingdom biofilms support Candida albicans growth under fluoride and attenuate the in vitro anti-caries effect of fluorine

Fluoride-resistant Streptococcus mutans (S. mutans) might affect the ecological balance of biofilms in the presence of fluoride. We used a S. mutans and Candida albicans (C. albicans) cross-kingdom biofilm model to investigate whether fluoride-resistant S. mutans in biofilms would support C. albicans growth under fluoride stress and attenuate the in vitro anti-caries effect of fluorine. The impact of fluoride-resistant S. mutans on formation of cross-kingdom biofilms by S. mutans and C. albicans in the presence of fluoride was investigated in vitro using the crystal violet staining assay. Biofilm constitution was determined using colony-forming unit (CFU) counts and fluorescent in situ hybridization (FISH). Extracellular polysaccharide (EPS) generation in biofilms was determined by EPS/bacterial dying and water-insoluble polysaccharide detection. Acid production and demineralization were monitored using pH, lactic acid content, and transversal microradiography (TMR). The gene expression of microorganisms in the cross-kingdom biofilm was measured using qRT-PCR. Our results showed that both C. albicans and fluoride-resistant S. mutans grew vigorously, forming robust cross-kingdom biofilms, even in the presence of sodium fluoride (NaF). Moreover, fluoride-resistant S. mutans-containing cross-kingdom biofilms had considerable cariogenic potential for EPS synthesis, acid production, and demineralization ability in the presence of NaF than fluoride-sensitive S. mutans-containing biofilms. Furthermore, the gene expression of microorganisms in the two cross-kingdom biofilms changed dissimilarly in the presence of NaF. In summary, fluoride-resistant S. mutans in cross-kingdom biofilms supported C. albicans growth under fluoride and might attenuate the anti-caries potential of fluorine by maintaining robust cross-kingdom biofilm formation and cariogenic virulence expression in vitro in the presence of NaF.

ZnO nanoparticles induced biofilm formation in Klebsiella pneumoniae and Staphylococcus aureus at sub-inhibitory concentrations

Biofilm formation by the pathogenic bacteria generates a serious threat to the public health as it can increase the virulence potential, resistance to drugs, and escape from the host immune response mechanisms. Among the environmental factors that influence the biofilm formation, there are only limited reports available on the role of antimicrobial agents. During the antimicrobial drug administration or application for any purpose, the microbial population can expect to get exposed to the sub-minimum inhibitory concentration (sub-MIC) of the drug which will have an unprecedented impact on microbial responses. Hence, the study has been conducted to investigate the effects of sub-MIC levels of zinc oxide nanoparticles (ZnO NPs) on the biofilm formation of Klebsiella pneumoniae and Staphylococcus aureus. Here, the selected bacteria were primarily screened for the biofilm formation by using the Congo red agar method, and their susceptibility to ZnO NPs was also evaluated. Quantitative difference in biofilm formation by the selected organisms in the presence of ZnO NPs at the sub-MIC level was further carried out by using the microtiter plate-crystal violet assay. Further, the samples were subjected to atomic force microscopy (AFM) analysis to evaluate the properties and pattern of the biofilm modulated under the experimental conditions used. From these, the organisms treated with sub-MIC levels of ZnO NPs were found to have enhanced biofilm formation when compared with the untreated sample. Also, no microbial growth could be observed for the samples treated with the minimum inhibitory concentration (MIC) of ZnO NPs. The results observed in the study provide key insights into the impact of nanomaterials on clinically important microorganisms which demands critical thinking on the antimicrobial use of nanomaterials.

Nattokinase, a Subtilisin-like Alkaline-Serine Protease, Reduces Mutacin Activity by Inactivating the Competence-Stimulating Peptide in Streptococcus mutans

Streptococcus mutans is a major cariogenic organism because of its ability to form biofilms on tooth surfaces. Bacteriocins produced by S. mutans (known as mutacins) are indirect pathogenic factors that play a role in the persistence of this microbe in the oral environment. Nattokinase, a subtilisin-like alkaline serine protease, potently inhibits biofilm formation without affecting S. mutans growth. However, effective strategies utilizing nattokinase to control mutacin production by S. mutans are lacking. In this study, we evaluated the effect of nattokinase on mutacin activity in 46 strains of S. mutans with different mutacin genotypes isolated from the dental plaques of pediatric patients with caries. Nattokinase reduced the activity of mutacin against oral streptococci at a concentration of 1 mg/mL in all clinical isolates. Furthermore, nattokinase reduced the expression of non-lantibiotic mutacin structural genes (nlmABCD) and inactivated the extracellular competence-stimulating peptide involved in comDE activation, which regulates non-lantibiotic mutacin gene expression. These results suggest that nattokinase may reduce the virulence of S. mutans and could potentially be used as a new caries-preventive agent as an alternative to conventional drug treatments.

The Effect of Ficin Immobilized on Carboxymethyl Chitosan on Biofilms of Oral Pathogens

In the last decade, Ficin, a proteolytic enzyme extracted from the latex sap of the wild fig tree, has been widely investigated as a promising tool for the treatment of microbial biofilms, wound healing, and oral care. Here we report the antibiofilm properties of the enzyme immobilized on soluble carboxymethyl chitosan (CMCh) and CMCh itself. Ficin was immobilized on CMCh with molecular weights of either 200, 350 or 600 kDa. Among them, the carrier with a molecular weight of 200 kDa bound the maximum amount of enzyme, binding up to 49% of the total protein compared to 19-32% of the total protein bound to other CMChs. Treatment with pure CMCh led to the destruction of biofilms formed by Streptococcus salivarius, Streptococcus gordonii, Streptococcus mutans, and Candida albicans, while no apparent effect on Staphylococcus aureus was observed. A soluble Ficin was less efficient in the destruction of the biofilms formed by Streptococcus sobrinus and S. gordonii. By contrast, treatment with CMCh200-immobilized Ficin led to a significant reduction of the biofilms of the primary colonizers S. gordonii and S. mutans. In model biofilms obtained by the inoculation of swabs from teeth of healthy volunteers, the destruction of the biofilm by both soluble and immobilized Ficin was observed, although the degree of the destruction varied between artificial plaque samples. Nevertheless, combined treatment of oral Streptococci biofilm by enzyme and chlorhexidine for 3 h led to a significant decrease in the viability of biofilm-embedded cells, compared to solely chlorhexidine application. This suggests that the use of either soluble or immobilized Ficin would allow decreasing the amount and/or concentration of the antiseptics required for oral care or improving the efficiency of oral cavity sanitization.

The inhibitory effect of berberine chloride hydrate on Streptococcus mutans biofilm formation at different pH values

Streptococcus mutans (S. mutans) is one of the major cariogenic bacteria of dental caries owing to its ability to adhere to tooth surfaces and biofilm formation. Berberine chloride hydrate (BH), a quaternary ammonium salt alkaloid, has diverse pharmacological efforts against microorganisms. However, the effect of BH on S. mutans biofilm has not been reported. Considering that berberine is a quaternary ammonium salt alkaloid, which needs to adapt to a large variation in pH values and the acid resistance of S. mutans, we employed three groups including pH 5 (acidic), pH 8 (alkaline), and unprocessed group (neutral) to examine the antibiofilm activities of BH against S. mutans during different pH values. In this study, we found BH effectively suppresses S. mutans biofilm formation as well as its cariogenic virulence including acid production and EPS synthesis significantly, and the inhibitory effort was reduced under acidic condition whereas elevated under alkaline condition. In addition, we preliminarily explored the influence of pH values on the structural stability and biosafety of BHas well as the underlying mechanism of inhibition of S. mutans biofilm formation with BH. Our study showed BH could maintain a good structural stability and low toxicity to erythrocytes at different pH values. And BH could downregulate the expression of srtA, spaP, and gbpC, which play critical roles in the adhesion process, promoting bacterial colonization and biofilm formation. Furthermore, comX and ldh expression levels were downregulated in BH-treated group, which might explain its inhibitory effect on acid production.IMPORTANCEDental caries is a common chronic detrimental disease, which could cause a series of oral problem including oral pain, difficulties in eating, and so on. Recently, many natural products have been considered as fundamental sources of therapeutic drugs to prevent caries. Berberine as a plant extract showed good antibiofilm abilities against microorganism. Our study focuses on its antibiofilm abilities against S. mutans, which was defined as major cariogenic bacterium and explored the role of pH values and possible underlying mechanisms in the inhibitory effect of BH on S. mutans biofilm formation. This study demonstrated a promising prospect for BH as an adjuvant drug in the prevention and management of dental caries.

Effects of a Novel, Intelligent, pH-Responsive Resin Adhesive on Cariogenic Biofilms In Vitro

Background: Secondary caries often result in a high failure rate of resin composite restoration. Herein, we studied the dodecylmethylaminoethyl methacrylate−modified resin adhesive (DMAEM@RA) to investigate its pH-responsive antimicrobial effect on Streptococcus mutans and Candida albicans dual-species biofilms and on secondary caries. Methods: Firstly, the pH-responsive antimicrobial experiments including colony-forming units, scanning electron microscopy and exopoly-saccharide staining were measured. Secondly, lactic acid measurement and transverse microradiography analysis were performed to determine the preventive effect of DMAEM@RA on secondary caries. Lastly, quantitative real-time PCR was applied to investigate the antimicrobial effect of DMAEM@RA on cariogenic virulence genes. Results: DMAEM@RA significantly inhibited the growth, EPS, and acid production of Streptococcus mutans and Candida albicans dual-species biofilms under acidic environments (p < 0.05). Moreover, at pH 5 and 5.5, DMAEM@RA remarkably decreased the mineral loss and lesion depth of tooth hard tissue (p < 0.05) and down-regulated the expression of cariogenic genes, virulence-associated genes, and pH-regulated genes of dual-species biofilms (p < 0.05). Conclusions: DMAEM@RA played an antibiofilm role on Streptococcus mutans and Candida albicans dual-species biofilms, prevented the demineralization process, and attenuated cariogenic virulence in a pH-dependent manner.

Inhibitory effect of ficin on Candida albicans biofilm formation and pre-formed biofilms

BACKGROUND

To investigate the effect of ficin, a type of proteases, on Candida albicans (C. albicans) biofilm, including forming and pre-formed biofilms.

METHODS

Crystal violet tests together with colony forming unit (CFU) counts were used to detect fungal biofilm biomass. Live/dead staining of biofilms observed by confocal laser scanning microscopy was used to monitor fungal activity. Finally, gene expression of C. albicans within biofilms was assessed by qRT-PCR.

RESULTS

According to our results, biofilm biomass was dramatically reduced by ficin in both biofilm formation and pre-formed biofilms, as revealed by the crystal violet assay and CFU count (p < 0.05). Fungal activity in biofilm formation and pre-formed biofilms was not significantly influenced by ficin according to live/dead staining. Fungal polymorphism and biofilm associated gene expression were influenced by ficin, especially in groups with prominent antibiofilm effects.

CONCLUSIONS

In summary, ficin effectively inhibited C. albicans biofilm formation and detached its preformed biofilm, and it might be used to treat C. albicans biofilm associated problems.

Novel Immobilized Biocatalysts Based on Cysteine Proteases Bound to 2-(4-Acetamido-2-sulfanilamide) Chitosan and Research on Their Structural Features

Briefly, 2-(4-Acetamido-2-sulfanilamide) chitosan, which is a chitosan water-soluble derivative, with molecular weights of 200, 350, and 600 kDa, was successfully synthesized. The immobilization of ficin, papain, and bromelain was carried out by complexation with these polymers. The interaction mechanism of 2-(4-acetamido-2-sulfanilamide) chitosan with bromelain, ficin, and papain was studied using FTIR spectroscopy. It was found that the hydroxy, thionyl, and amino groups of 2-(4-acetamido-2-sulfanilamide) chitosan were involved in the complexation process. Molecular docking research showed that all amino acid residues of the active site of papain formed hydrogen bonds with the immobilization matrix, while only two catalytically valuable amino acid residues took part in the H-bond formation for bromelain and ficin. The spectral and in silico data were in good agreement with the catalytic activity evaluation data. Immobilized papain was more active compared to the other immobilized proteases. Moreover, the total and specific proteolytic activity of papain immobilized on the carrier with a molecular weight of 350 kDa were higher compared to the native one due to the hyperactivation. The optimal ratio of protein content (mg × g ⁻¹ of carrier), total activity (U × mL⁻¹ of solution), and specific activity (U × mg⁻¹ of protein) was determined for the enzymes immobilized on 2-(4-acetamido-2-sulfanilamide) chitosan with a molecular weight of 350 kDa.

Influence of Fluoride-Resistant Streptococcus mutans Within Antagonistic Dual-Species Biofilms Under Fluoride In Vitro

The widespread application of fluoride, an extremely effective caries prevention agent, induces the generation of fluoride-resistant strains of opportunistic cariogenic bacteria such as fluoride-resistant Streptococcus mutans (S. mutans). However, the influence of this fluoride-resistant strain on oral microecological homeostasis under fluoride remains unknown. In this study, an antagonistic dual-species biofilm model composed of S. mutans and Streptococcus sanguinis (S. sanguinis) was used to investigate the influence of fluoride-resistant S. mutans on dual-species biofilm formation and pre-formed biofilms under fluoride to further elucidate whether fluoride-resistant strains would influence the anti-caries effect of fluoride from the point of biofilm control. The ratio of bacteria within dual-species biofilms was investigated using quantitative real-time PCR and fluorescence in situ hybridization. Cristal violet staining, scanning electron microscopy imaging, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay were used to evaluate biofilm biomass, biofilm structure, and metabolic activity, respectively. Biofilm acidogenicity was determined using lactic acid and pH measurements. The anthrone method and exopolysaccharide (EPS) staining were used to study the EPS production of biofilms. We found that, in biofilm formation, fluoride-resistant S. mutans occupied an overwhelming advantage in dual-species biofilms under fluoride, thus showing more biofilm biomass, more robust biofilm structure, and stronger metabolic activity (except for 0.275 g/L sodium fluoride [NaF]), EPS production, and acidogenicity within dual-species biofilms. However, in pre-formed biofilms, the advantage of fluoride-resistant S. mutans could not be fully highlighted for biofilm formation. Therefore, fluoride-resistant S. mutans could influence the anti-caries effect of fluoride on antagonistic dual-species biofilm formation while being heavily discounted in pre-formed biofilms from the perspective of biofilm control.

Antibacterial and Antibiofilm Effect of Cell-Free Supernatant of Lactobacillus brevis KCCM 202399 Isolated from Korean Fermented Food against Streptococcus mutans KCTC 5458

This study aims to determine the antibiofilm effect of cell-free supernatant (CFS) of Lactobacillus brevis strains against Streptococcus mutans strains. To study the antibiofilm mechanism against S. mutans strains, antibacterial effects, cell surface properties (auto-aggregation and cell surface hydrophobicity), exopolysaccharide (EPS) production, and morphological changes were examined. The antibiofilm effect of L. brevis KCCM 202399 CFS as morphological changes were evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), compared with the control treatment. Among the L. brevis strains, L. brevis KCCM 202399 showed the highest antibiofilm effect on S. mutans KCTC 5458. The antibacterial effect of L. brevis KCCM 202399 against S. mutans KCTC 5458 was investigated using the deferred method (16.00 mm). The minimum inhibitory concentration of L. brevis KCCM 202399 against S. mutans KCTC 5458 was 25.00%. Compared with the control treatment, L. brevis KCCM 202399 CFS inhibited the bacterial adhesion of S. mutans KCTC 5458 by decreasing auto-aggregation, cell surface hydrophobicity, and EPS production (45.91%, 40.51%, and 67.44%, respectively). L. brevis KCCM 202399 CFS inhibited and eradicated the S. mutans KCTC 5458 biofilm. Therefore, these results suggest that L. brevis KCCM 202399 CFS may be used to develop oral health in the probiotic industry.

Small Molecule Compounds, A Novel Strategy against Streptococcus mutans

Dental caries, as a common oral infectious disease, is a worldwide public health issue. Oral biofilms are the main cause of dental caries. Streptococcus mutans (S. mutans) is well recognized as the major causative factor of dental caries within oral biofilms. In addition to mechanical removal such as tooth brushing and flossing, the topical application of antimicrobial agents is necessarily adjuvant to the control of caries particularly for high-risk populations. The mainstay antimicrobial agents for caries such as chlorhexidine have limitations including taste confusions, mucosal soreness, tooth discoloration, and disruption of an oral microbial equilibrium. Antimicrobial small molecules are promising in the control of S. mutans due to good antimicrobial activity, good selectivity, and low toxicity. In this paper, we discussed the application of antimicrobial small molecules to the control of S. mutans, with a particular focus on the identification and development of active compounds and their modes of action against the growth and virulence of S. mutans.