Inhibition of the activity of glucosyltransferase from Streptococcus mutans by glycyrrhizin

We have previously shown that the natural sweetener glycyrrhizin (glyc) inhibits in vitro adherence of Streptococcus mutans in the presence of sucrose. In order to further examine the mechanism of adherence inhibition, extracellular glucosyltransferase of S. mutans was obtained, and its ability to produce glucans from sucrose in the presence of glyc was tested. These results indicate that glyc inhibits bacterial adherence by affecting the activity of glucosyltransferase.     

Resazurin metabolism assay for root canal disinfectant evaluation on dual-species biofilms

Introduction

Endodontic infections are caused by polymicrobial biofilms. Therefore, novel root canal disinfectants should be evaluated not only on single-species biofilms but also on dual- or mixed-species biofilms. A simple, high-throughput assay is urgently needed for this. In this study, the application of the resazurin metabolism assay was investigated for the evaluation of a root canal disinfectant on dual-species biofilms.

Methods

Enterococcus faecalis with or without Streptococcus mutans in biofilms were formed in an active attachment biofilm model for 24 hours. Subsequently, the biofilms were treated with various concentrations of NaOCl for 1 minute. After resazurin metabolism by both organisms was confirmed, treatment efficacies using 0.0016% resazurin were evaluated.

Results

During NaOCl treatments, resazurin metabolism displays a clear dose response, not only in single-species E. faecalis (or S. mutans) biofilms but also in dual-species biofilms. Notably, the assay revealed that the resistance of dual-species biofilms to NaOCl was 30-fold higher than in single-species E. faecalis biofilms. Viability counts on a selected NaOCl treatment (0.004%) confirmed this result and showed the increased resistance of E. faecalis in dual-species biofilms.

Conclusions

Clearly, the high-throughput and low cost resazurin metabolism assay has a great potential for testing novel root canal antimicrobial agents in mixed-species biofilms.     

Antimicrobial susceptibility of 1042 strains of Streptococcus mutans and Streptococcus sobrinus: comparison from 1985 to 1989

A total of 1042 strains of Streptococcus mutans and Streptococcus sobrinus isolated between 1985 and 1989 were tested to study the evolution of their sensitivity to penicillin, amoxycillin, amoxycillin/clavulanic acid, cefuroxime, tetracycline, erythromycin, spiramycin, acetyl spiramycin, lincomycin and clindamycin. The strains were taken from stock cultures and isolated from human saliva and dental plaque. The minimal inhibitory concentration (MIC) was determined by an agar dilution method. Except for spiramycin and acetyl spiramycin, all the antibiotics inhibited 100% of the strains with concentrations less than or equal to 2 micrograms/ml. Microorganisms from both species underwent a slow progressive loss of sensitivity to all the antibiotics over a 5-year period of study, showing statistically significant results in most cases.     

Effect of antibodies on chemiluminescence and on killing of Streptococcus sobrinus by polymorphonuclear leukocytes

The effect of a polyclonal antiserum and OMVU10, a monoclonal antibody reactive with Antigen B of Streptococcus sobrinus , on the interaction of polymorphonuclear leukocytes with S. sobrinus was studied, using chemiluminescence and bacterial killing assays. Increased stimulation of neutrophils as measured in the chemiluminescence assays was established when S. sobrinus was preincubated with polyclonal antiserum or when polyclonal antiserum was added to the reaction mixture. Higher counts were measured in comparison to preimmune serum. After 90 min, 52% of S. sobrinus preincubated with polyclonal antiserum was killed. Killing was also increased when polyclonal antiserum was added to the reaction mixture in comparison to the controls. No killing was found when bacteria were preincubated with OMVU10 or when OMVU10 was added to the reaction mixture in comparison to Clone 24, a control antibody.     

五倍子对致龋菌抑制作用的实验研究

目的：观察五倍子对致龋菌抑制作用并测定最小抑菌浓度、最小杀菌浓度。方法：对五倍子分别采用水、乙醇两种方法提取有效成分，通过纸片扩散法研究对致龋菌的抑制作用，用液体稀释方法检测最小抑菌浓度、最小杀菌浓度。结果：五倍子水提取物对变形链球菌Ingbritt株、茸毛链球菌6715株、粘性放线菌ATCC 19246株的抑菌圈分别为20．41mm、10．46mm、6．74mm；对变形链球菌Ingbritt株最小抑菌浓度为15．6g／L；最小杀菌浓度为15．6g／L；五倍子醇提取物对变形链球菌Ingbritt株、茸毛链球菌6715株、粘性放线菌ATCC 1 9246株的抑菌圈分别为20．71mm、14．87mm、6．57mm；对变形链球菌Ingbritt株、茸毛链球菌6715株最小抑菌浓度为1．95g／L、3．9s／L；最小杀菌浓度为3．9g／L、3．9g／L。结论：五倍子水、醇提取物对变形链球菌Ingbritt株、茸毛链球菌6715株有较强的抑菌或杀菌作用．对粘性放线菌ATCC 19246株没有抑菌作用     

远缘链球菌g型对铸钛、钴铬合金、镍铬合金修复体腐蚀失泽的研究

目的:研究远缘链球菌g 型对铸钛、Co-Cr 合金、Ni-Cr 合金修复体失泽腐蚀的影响。方法:将Co-Cr 合金、Ni-Cr合金、纯钛分别铸造制备成10 mm×10 mm×1 mm板片,每组30 片。将上述3 组每组随机分空白对照组,培养基对照组、实验组各10 片。需氧环境中,将g 型远缘链球菌接种到蔗糖琼脂培养基后,将试件贴附其表面,每周转换传递一次,共10 周。0105 %戊二醛消灭细菌,清洗,2 周后用MINOLTA CR-100 型色度计观察。结果:经统计学分析可知铸钛、Co-Cr 合金、Ni-Cr 合金修复体的空白对照组与培养基对照组的L*、a*、b*值无显著差异( P > 0105) 。铸钛、Co-Cr 合金、Ni-Cr 合金修复体实验组与空白对照组、培养基对照组的L*、a*、b*值有明显差异( P < 0105) 。结论:按CIE1976 标准检测得出远缘链球菌g 型对Co-Cr 合金、Ni-Cr 合金、铸钛修复体色泽有影响,但未超出黄绿区域。     

Genomic variation in Streptococcus mutans: deletions affecting the multiple pathways of β‐glucoside metabolism

The genome of Streptococcus mutans UA159 contains two phospho‐β‐glucosidase genes, bglA and celA, which occur in operon‐like arrangements along with genes for components of phosphotransferase transport systems and a third phospho‐β‐glucosidase encoded by the arb gene, which does not have its own associated transport system but relies on uptake by the bgl or cel systems. Targeted inactivation of each of the phospho‐β‐glucosidase genes revealed that bglA is involved in aesculin hydrolysis, celA is essential for utilisation of cellobiose, amygdalin, gentobiose and salicin, and arb is required for utilisation of arbutin. Inactivation of genes for the phosphotransferase systems revealed an overlap of specificity for transport of β‐glucosides and also indicated that further, unidentified transport systems exist. The cel and arb genes are subject to catabolite repression by glucose, but the regM gene is not essential for catabolite repression. Screening a collection of isolates of S. mutans revealed strains with deletions affecting the msm, bgl and/or cel operons. The phenotypes of these strains could largely be explained on the basis of the results obtained from the knockout mutants of S. mutans UA159 but also indicated the existence of other pathways apparently absent from UA159. The extensive genetic and phenotypic variation found in β‐glucoside metabolism indicates that there may be extensive heterogeneity in the species.     

Antibacterial effect of ozone on cariogenic bacterial species

Objective

The aim was to evaluate the antibacterial effect of ozone on cariogenic bacterial species with and without the presence of saliva and a possible effect on the salivary proteins.

Methods

Suspensions of Actinomyces naeslundii (ACTCC 12104^T), Lactobacilli casei (N CTC 151) and Streptococcus mutans (NCTC 10449), in salt buffer or in saliva, were exposed to ozone gas delivered by the ozone generator Healozone™ 2130C. Aliquots of the suspensions were taken after 10, 30 and 60 s ozone exposures and cultivated on agar plates. Initial number of bacteria per ml was 8.0 × 10⁷ (SD 2.2 × 10⁷) (A. naeslundii), 1.0 × 10⁸ (SD 3.1 × 10⁶) (L. casei) and 1.0 × 10⁸ (SD 7.0 × 10⁵) (S. mutans), respectively. The proteins were separated by SDS electrophoresis and visualized by silver staining.

Results

In salt buffer 92%, 73% and 64% of the initial numbers of A. naeslundii, S. mutans and L. casei, respectively, were killed already after 10 s ozone exposure, while approximately 99.9% of the bacteria were dead after a 60 s exposure. After 10 and 30 s, but not after 60 s exposure to ozone, S. mutans and L. casei were less efficiently killed in saliva compared to the salt buffer. Various saliva proteins were degraded by ozone after a 60 s exposure.

Conclusions

The cariogenic species S. mutans, L. casei and A. naeslundii were almost eliminated following 60 s of ozone treatment. This killing was reduced in the presence of saliva although increasing the ozone application time to 60 s overcame these reductants in saliva. Detection of altered salivary proteins indicates that saliva components constitute additional targets for ozone.     

The influence of 30-day-old Streptococcus mutans biofilm on the surface of esthetic restorative materials--an in vitro study

OBJECTIVE: To evaluate the effects of Streptococcus mutans biofilm/restorative materials interaction on surface roughness, hardness and morphology of materials tested. METHODS: Empress 2 (E2), Filtek Supreme (FS), Vitremer (V) and Ketac Molar Easymix (KM) were tested. Twenty-five disks of each material were made and divided into three storage groups: (1) 100% relative humidity (n=5); (2) growth medium (BHI and 1% sucrose) (n=5); (3) S. mutans biofilm-growth medium (n=15). Before storage, hardness measurements were immediately obtained from group 1 specimens. After 30 days of storage, the specimens were cleaned in order to obtain the surface roughness and hardness values, besides morphology analysis by scanning electron microscopy. RESULTS: The surface roughness and hardness values obtained from E2 and FS specimens did not present statistically significant differences among the groups 1, 2 and 3 and between immediate and 30-day-old specimens of each material. However, group 3 specimens of V and KM showed statistically significant higher surface roughness means than other groups. Group 1 specimens of V and KM also showed higher hardness values than the immediate values. Group 3 specimens of V presented decreased hardness values compared with other groups. The scanning electron micrographs showed an increase in surface degradation from group 1 to group 3 for FS, V and KM. CONCLUSIONS: Thirty-day-old biofilm promotes a negative effect on the surface morphology of FS, V and KM, on the surface roughness of V and KM and on the hardness of V.     

Effects of apigenin and tt‐farnesol on glucosyltransferase activity,biofilm viability and caries development in rats

Propolis, a resinous hive product secreted by Apis mellifera bees, has been shown to reduce the incidence of dental caries in rats. Several compounds, mainly polyphenolics, have been identified in propolis. Apigenin and tt‐farnesol demonstrated biological activity against mutans streptococci. We determined here their effects, alone or in combination, on glucosyltransferase activity, biofilm viability, and development of caries in rats. Sprague‐Dawley rats were infected with Streptococcus sobrinus 6715 and treated topically twice daily as follows: (1) tt‐farnesol, (2) apigenin, (3) vehicle control, (4) fluoride, (5) apigenin +tt‐farnesol, and (6) chlorhexidine. Apigenin (1.33 mM) inhibited the activity of glucosyltransferases in solution (90–95%) and on the surface of saliva‐coated hydroxyapatite beads (35–58%); it was devoid of antibacterial activity. tt‐Farnesol (1.33 mM) showed modest antibacterial activity against biofilms and its effects on glucosyltransferases were minimal. The incidence of smooth‐surface caries was significantly reduced by apigenin +tt‐farnesol (60%), fluoride (70%), and chlorhexidine (72%) treatments compared to control (P < 0.05).