Further studies on extracellular glucans synthesized by glucosyltransferases of oral streptococci

Important Roles and Potential Uses of Natural and Synthetic Antimicrobial Peptides (AMPs) in Oral Diseases: Cavity, Periodontal Disease, and Thrush

Numerous epithelial cells and sometimes leukocytes release AMPs as their first line of defense. AMPs encompass cationic histatins, defensins, and cathelicidin to encounter oral pathogens with minimal resistance. However, their concentrations are significantly below the effective levels and AMPs are unstable under physiological conditions due to proteolysis, acid hydrolysis, and salt effects. In parallel to a search for more effective AMPs from natural sources, considerable efforts have focused on synthetic stable and low-cytotoxicy AMPs with significant activities against microorganisms. Using natural AMP templates, various attempts have been used to synthesize sAMPs with different charges, hydrophobicity, chain length, amino acid sequence, and amphipathicity. Thus far, sAMPs have been designed to target Streptococcus mutans and other common oral pathogens. Apart from sAMPs with antifungal activities against Candida albicans, future endeavors should focus on sAMPs with capabilities to promote remineralization and antibacterial adhesion. Delivery systems using nanomaterials and biomolecules are promising to stabilize, reduce cytotoxicity, and improve the antimicrobial activities of AMPs against oral pathogens. Nanostructured AMPs will soon become a viable alternative to antibiotics due to their antimicrobial mechanisms, broad-spectrum antimicrobial activity, low drug residue, and ease of synthesis and modification.

Chemical composition and antibacterial activity of Berberis vulgaris (barberry) against bacteria associated with caries

Objectives

The aim of this in‐vitro study was to determine the antimicrobial capacity of a Berberis vulgaris plant extract on the bacteria being associated with caries including, Streptococcus mutans, S. sobrinus, S. sanguinis, S. salivaris and Lactobacillus rhamnosus.

Material and methods

Chlorhexidine 2% (CHX) mouthwash and ampicillin (10 μg/disk) were applied as positive control groups. Inhibition zone, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) related to stem, leaf and fruit of B. vulgaris plant were recorded for every five bacteria. Data were analyzed using SPSS ver. 22, one‐way ANOVA repeated measure and post hoc Tukey statistical test. The significance level was set at p < 0.05.

Results

There were no significant differences between the antimicrobial capacity of the positive controls and the extract from the stem and fruit of B. vulgaris (p > 0.05). The MIC values of the extract from the stem were significantly lower against S. sobrinus (64 μg/ml) and L. rhamnosus (128 μg/ml). The MIC value of the extract against S. mutans was significantly lower in the fruit group (64 μg/mL). The MBC value of the extract against S. sobrinus and L. rhamnosus was significantly lower in the stem group (128 μg/ml). The MBC value against S. mutans was significantly lower in the fruit group (128 μg/ml).

Conclusions

The results showed that CHX and B. vulgaris plant extract have similar antimicrobial activity against bacteria being associated with caries. Therefore, B. vulgaris, which shows antibacterial capacity, could be considered for further investigation as a safe, phytotherapeutic mouthwash to prevent dental caries.

Application of Antibiotics/Antimicrobial Agents on Dental Caries

Dental caries is the most common oral disease. The bacteriological aetiology of dental caries promotes the use of antibiotics or antimicrobial agents to prevent this type of oral infectious disease. Antibiotics have been developed for more than 80 years since Fleming discovered penicillin in 1928, and systemic antibiotics have been used to treat dental caries for a long time. However, new types of antimicrobial agents have been developed to fight against dental caries. The purpose of this review is to focus on the application of systemic antibiotics and other antimicrobial agents with respect to their clinical use to date, including the history of their development, and their side effects, uses, structure types, and molecular mechanisms to promote a better understanding of the importance of microbial interactions in dental plaque and combinational treatments.

Microbial dextran-hydrolyzing enzymes: fundamentals and applications

Dextran is a chemically and physically complex polymer, breakdown of which is carried out by a variety of endo- and exodextranases. Enzymes in many groups can be classified as dextranases according to function: such enzymes include dextranhydrolases, glucodextranases, exoisomaltohydrolases, exoisomaltotriohydrases, and branched-dextran exo-1,2-alpha-glucosidases. Cycloisomalto-oligosaccharide glucanotransferase does not formally belong to the dextranases even though its side reaction produces hydrolyzed dextrans. A new classification system for glycosylhydrolases and glycosyltransferases, which is based on amino acid sequence similarities, divides the dextranases into five families. However, this classification is still incomplete since sequence information is missing for many of the enzymes that have been biochemically characterized as dextranases. Dextran-degrading enzymes have been isolated from a wide range of microorganisms. The major characteristics of these enzymes, the methods for analyzing their activities and biological roles, analysis of primary sequence data, and three-dimensional structures of dextranases have been dealt with in this review. Dextranases are promising for future use in various scientific and biotechnological applications.

Dextran-induced aggregation in a mutant of Streptococcus sobrinus 6715-13

A mutant of wild-type Streptococcus sobrinus 6715-13 has been isolated which resists aggregation by exogenous dextran. This variant is able to form adherent plaque deposits in vitro when cultured in the presence of sucrose and has dextranase activity. In these respects it is the complement of previously described isolates which are plaque formation defective but aggregation normal. Measurements of the incorporation of glucose from glucosyl-labeled sucrose into glucan by cell-associated glucosyltransferase enzyme activity and the thermal labilities of catalytic and receptor functions, as well as the binding of labeled dextrans to the cells, provide evidence that neither dextranase nor glucosyltransferase is the receptor involved in dextran-induced aggregation. Blockage of such bacterial aggregation by anti-glucosyltransferase or anti-dextranase sera suggests cross-reactivity between the antigenic determinants of proteins which recognize alpha(1-6) glucan linkages. A model is proposed, consistent with these and previous findings, in which enzymatic function precedes dextran receptor activity in emergence from the cell. It is also proposed that dextran receptor components of the multireactive glucosyltransferase enzyme(s) and dextranase(s) are spatially separate from, although functionally and antigenically related to, the receptors on the bacterial surface involved in dextran-induced aggregation.

A comparative study of extracellular glucanhydrolase and glucosyltransferase enzyme activities of five different serotypes of oral Streptococcus mutans

The activities of glucanhydrolase (EC 3.2.1.11) and glucosyltransferase (EC 2.4.1.5) in crude enzyme preparations of 44 strains of Streptococcus mutans of five serotypes were investigated. The strains were grown in a laboratory fermentor for 16 h and the enzymes were isolated by adding solid ammonium sulphate to the culture supernatant, resulting in a 12-fold enrichment of the enzymes. For glucanhydrolase, strains of serotype a showed the lowest total activity (0.768 U, approx. 120 ml), whereas strains of serotype d had an activity 39 times higher (29.9 U). The total activities of strains of serotypes b, c and e were 5.56, 6.30 and 7.06 U, respectively. For glucosyltransferase, strains of type e showed the highest total activity (293 U), whereas differences between strains of the other four types were insignificant (type a: 158 U; type b: 175 U; type c: 191 U; type d: 225 U; approx. 120 ml). A strong correlation was found between the glucanhydrolase activity and the percentage of insoluble glucan synthesized in vitro by the respective strains. This correlation was not substantially changed if the enzyme activities were expressed as specific activities, or as total activities against bacterial weight.

Extracellular polysaccharide synthesized by the oral bacterium Streptococcus mutans of serotype a to e in vitro

Extracellular polysaccharide (EPS) synthesized in vitro by Streptococcus mutans belonging to serotypes a, b, c, d and e was shown to consist mainly of glucan. Only strains of type b and e regularly produced substantial amounts of fructan, too. Strains of type d synthesized significantly higher quantities of glucan than strains of the other types per gram of bacterial mass. The percentage of insoluble glucan was lowest in samples from strains of type a and c, and highest in samples from strains of type d. In contrast to the insoluble glucan, the linkage pattern of the soluble glucan of the five types showed only small differences. The percentage of alpha-1,3-linked glucose units was highest in the insoluble glucan from strains of type d and e, and lowest in glucan from type c. The differences were significant. Incubation of Strep. mutans under various culture conditions showed that the quantities and composition of EPS formed depend on the culture condition used. The effect of culture conditions, however, was similar for all strains. Therefore the differences found with respect to the quantities and composition of EPS synthesized in vitro by Strep. mutans of different types are apparently type-dependent.

Determination, by carbon-13 nuclear magnetic resonance spectroscopy, of the composition of glucans synthesized by enzymes of the cariogenic organism Streptococcus mutans

The 13C-n.m.r. spectra of water-soluble and -insoluble glucans synthesized by enzymes isolated from six strains of Streptococcus mutans are interpreted. The glucans are shown to be composed primarily of alpha-(1 linked to 3)- and alpha-(1 linked to 6)-linked glucosyl residues, and the relative abundance of each linkage is estimated from peak areas. Treatment of water-insoluble glucans with dextranase is found to result in water-soluble and -insoluble products, the former enriched in alpha-(1 linked to 6)-linkages and the latter in alpha-(1 linked to 3)-linkages. The structural conclusions arrived at by 13C-n.m.r. spectroscopy are consistent with data from methylation analysis and 1H-n.m.r. spectroscopy.

Metabolism of the polysaccharides of human dental plaque. Part II. Purification and properties of Cladosporium resinae (1 leads to 3)-alpha-D-glucanase, and the enzymic hydrolysis of glucans synthesised by extracellular D-glucosyltransferases of oral streptococci

Cladosporium resinae (1 leads to 3)-alpha-D-glucanase has been characterized as an endoglucanase capable of completely hydrolysing insoluble (1 leads to 3)-alpha-D-glucans isolated from fungal cell-walls. D-Glucose was the major product, but a small amount of nigerose was also produced. The enzyme was specific for the hydrolysis of (1 leads to 3) bonds that occur in sequence, and nigerotetraose was the smallest substrate that was rapidly attacked. Isolated (1 leads to 3)-alpha-D-glucosidic linkages that occur in mycodextran, isolichein, dextrans, and oligosaccharides derived from dextran were not hydrolysed. Insoluble glucan synthesised from sucrose by culture filtrates of Streptococcus spp. were all hydrolysed to various limits; the range was 11-61%. A soluble glucan, synthesised by an extracellular D-glucosyltransferase of S. mutans OMZ176, was not a substrate, whereas insoluble glucans synthesised by a different D-glucosyltransferase, isolated from S. mutans strains OMZ176 and K1-R, were extensively hydrolysed (84 and 92%, respectively). It is suggested that dextranase-CB, a bacterial endo(1 leads to 6)-alpha-D-glucanase that does not release D-glucose from any substrate, could be used together with C. resinae (1 leads to 3)-alpha-D-glucanase to determine the relative proportions of (1 leads to 6)-linked to (1 leads to 3)-linked sequences of D-glucose residues in the insoluble glucans produce by oral streptococci. The simultaneous action of the two D-glucanoses was highly effective in solubilizing the glucans.