Identification of mutans streptococcal species by the PCR products of the dex genes

Antibacterial effect of copper-bearing titanium alloy (Ti-Cu) against Streptococcus mutans and Porphyromonas gingivalis

Formation of bacterial biofilms on dental implant material surfaces (titanium) may lead to the development of peri-implant diseases influencing the long term success of dental implants. In this study, a novel Cu-bearing titanium alloy (Ti-Cu) was designed and fabricated in order to efficiently kill bacteria and discourage formation of biofilms, and then inhibit bacterial infection and prevent implant failure, in comparison with pure Ti. Results from biofilm based gene expression studies, biofilm growth observation, bacterial viability measurements and morphological examination of bacteria, revealed antimicrobial/antibiofilm activities of Ti-Cu alloy against the oral specific bacterial species, Streptococcus mutans and Porphyromonas gingivalis. Proliferation and adhesion assays with mesenchymal stem cells, and measurement of the mean daily amount of Cu ion release demonstrated Ti-Cu alloy to be biocompatible. In conclusion, Ti-Cu alloy is a promising dental implant material with antimicrobial/antibiofilm activities and acceptable biocompatibility.

Molecular Characterization of Dextranase fromStreptococcus rattus

The complete nucleotide sequence of the dextranase gene of Streptococcus rattus ATCC19645 was determined. An open reading frame of the dextranase gene was 2,760 bp long and encoded a dextranase protein consisting of 920 amino acids with a molecular weight of 100,163 Da and an isoelectric point of 4.67. The S. rattus dextranase purified from recombinant Escherichia coli cells showed dextran-hydrolyzing activity with optimal pH (5.0) and temperature (40 C) similar to those of dextranases from Streptococcus mutans and Streptococcus sobrinus. The deduced amino acid sequence of the S. rattus dextranase revealed that the dextranase molecule consists of two variable regions and a conserved region. The variable regions contained an N-terminal signal peptide and a C-terminal cell wall sorting signal; the conserved region contained two functional domains, catalytic and dextran-binding sites. This structural feature of the S. rattus dextranase is quite similar to that of other cariogenic species such as S. mutans, S. sobrinus, and Streptococcus downei.

Establishment of Streptococcus mutans in infants induces decrease in the proportion of salivary α-haemolytic bacteria

OBJECTIVE

For paediatric dentists, an indicator to assess caries risk of infants is very important. Conventionally, the number and/or proportions of Streptococcus mutans have been employed as risk indicator; however, because such figures reflect the existing situation, they are not suitable for assessing caries risk of infants that have not yet been infected with S. mutans. Thus, we searched for an indicator for the establishment of S. mutans.

METHODS

To evaluate the changes caused by the establishment of S. mutans in the microbiota of the infant oral cavity, we monitored changes in the oral microbiota of two pre-dentate infants over a 3-year period and in a cross-sectional study of 40 nursery school-aged children by cultivation of saliva on nonselective blood agar, Mitis-Salivarius agar, and Mitis-Salivarius agar supplemented with bacitracin combined with identification of selected isolates.

RESULTS

Two longitudinal observations suggested that the establishment of S. mutans would induce a decrease in α-haemolytic bacteria in the microbial population of the oral cavity. This suggestion was compensated with the results of cross-sectional study, and it was revealed that the establishment of 10(3)  CFU/mL of mutans streptococci in saliva might be predicted by a microbiota comprising less than approximately 55% of α-haemolytic.

CONCLUSION

Decrease in the proportion of α-haemolytic bacteria in saliva of infant was found to be applicable as an indicator to predict the establishment of S. mutans and to assess dental caries risk as a background for planning of dental care and treatment in the infants before infection with S. mutans.

Exploring internal features of 16S rRNA gene for identification of clinically relevant species of the genus Streptococcus

BACKGROUND

Streptococcus is an economically important genus as a number of species belonging to this genus are human and animal pathogens. The genus has been divided into different groups based on 16S rRNA gene sequence similarity. The variability observed among the members of these groups is low and it is difficult to distinguish them. The present study was taken up to explore 16S rRNA gene sequence to develop methods that can be used for preliminary identification and can supplement the existing methods for identification of clinically-relevant isolates of the genus Streptococcus.

METHODS

16S rRNA gene sequences belonging to the isolates of S. dysgalactiae, S. equi, S. pyogenes, S. agalactiae, S. bovis, S. gallolyticus, S. mutans, S. sobrinus, S. mitis, S. pneumoniae, S. thermophilus and S. anginosus were analyzed with the purpose to define genetic variability within each species to generate a phylogenetic framework, to identify species-specific signatures and in-silico restriction enzyme analysis.

RESULTS

The framework based analysis was used to segregate Streptococcus spp. previously identified upto genus level. This segregation was validated using species-specific signatures and in-silico restriction enzyme analysis. 43 uncharacterized Streptococcus spp. could be identified using this approach.

CONCLUSIONS

The markers generated exploring 16S rRNA gene sequences provided useful tool that can be further used for identification of different species of the genus Streptococcus.

Partial recN gene sequencing: a new tool for identification and phylogeny within the genus Streptococcus

Partial sequences of the recN gene (1249 bp), which encodes a recombination and repair protein, were analysed to determine the phylogenetic relationship and identification of streptococci. The partial sequences presented interspecies nucleotide similarity of 56.4-98.2 % and intersubspecies similarity of 89.8-98 %. The mean DNA sequence similarity of recN gene sequences (66.6 %) was found to be lower than those of the 16S rRNA gene (94.1 %), rpoB (84.6 %), sodA (74.8 %), groEL (78.1 %) and gyrB (73.2 %). Phylogenetically derived trees revealed six statistically supported groups: Streptococcus salivarius, S. equinus, S. hyovaginalis/S. pluranimalium/S. thoraltensis, S. pyogenes, S. mutans and S. suis. The 'mitis' group was not supported by a significant bootstrap value, but three statistically supported subgroups were noted: Streptococcus sanguinis/S. cristatus/S. sinensis, S. anginosus/S. intermedius/S. constellatus (the 'anginosus' subgroup) and S. mitis/S. infantis/S. peroris/S. oralis/S. oligofermentans/S. pneumoniae/S. pseudopneumoniae. The partial recN gene sequence comparison highlighted a high percentage of divergence between Streptococcus dysgalactiae subsp. dysgalactiae and S. dysgalactiae subsp. equisimilis. This observation is confirmed by other gene sequence comparisons (groEL, gyrB, rpoB and sodA). A high percentage of similarity was found between S. intermedius and S. constellatus after sequence comparison of the recN gene. To study the genetic diversity among the 'anginosus' subgroup, recN, groEL, sodA, gyrB and rpoB sequences were determined for 36 clinical isolates. The results that were obtained confirmed the high genetic diversity within this group of streptococci.

Principles and applications of polymerase chain reaction in medical diagnostic fields: a review

Recent developments in molecular methods have revolutionized the detection and characterization of microorganisms in a broad range of medical diagnostic fields, including virology, mycology, parasitology, microbiology and dentistry. Among these methods, Polymerase Chain Reaction (PCR) has generated great benefits and allowed scientific advancements. PCR is an excellent technique for the rapid detection of pathogens, including those difficult to culture. Along with conventional PCR techniques, Real-Time PCR has emerged as a technological innovation and is playing an ever-increasing role in clinical diagnostics and research laboratories. Due to its capacity to generate both qualitative and quantitative results, Real-Time PCR is considered a fast and accurate platform. The aim of the present literature review is to explore the clinical usefulness and potential of both conventional PCR and Real-Time PCR assays in diverse medical fields, addressing its main uses and advances.

Quantitative real-time polymerase chain reaction for Streptococcus mutans and Streptococcus sobrinus in dental plaque samples and its association with early childhood caries

BACKGROUND

Streptococcus mutans and Streptococcus sobrinus are closely associated with the development of early childhood caries (ECC). Recently, quantitative real-time polymerase chain reaction (qRT-PCR) has been used for rapid and accurate quantification of these bacterial species.

AIM

This study aims to detect quantitatively the levels of S. mutans and S. sobrinus in plaque samples by qRT-PCR, and to assess their association with the prevalence of ECC in Korean preschool children.

DESIGN

One hundred and five children (71 months old or younger) were examined and classified into three groups (caries-free, ECC, severe ECC). Dental plaque samples were collected and qRT-PCR was conducted using oligonucleotide primers specific for glucosyltransferase gene (S. mutans-gtfB, S. sobrinus-gtfU) and universal primer. Pearson's correlation test was conducted to evaluate the relationship between the dmfs (decayed, missing, or filled surfaces primary teeth) scores and the microbiological findings.

RESULTS

There was a significant difference between the levels of S. mutans and S. sobrinus in the plaque samples of the three groups (P < 0.05). The proportion of S. sobrinus to S. mutans showed strong correlation to the dmfs scores (r = 0.748, P < 0.05).

CONCLUSIONS

The qRT-PCR results of this study showed that children with ECC had higher level of S. mutans and S. sobrinus in their dental plaque samples. The children with higher ratio of S. sobrinus to S. mutans in their dental plaque showed higher incidence of ECC.

Identification and characterization of a dextranase gene of Streptococcus criceti

The dextranase gene, dex, was identified in Streptococcus criceti strain E49 by degenerate PCR and sequenced completely by the gene-walking method. A sequence of 3,960 nucleotides was determined. The dex gene encodes a 1,200-amino acid protein, which has a calculated molecular mass of 128,129.91 and pI of 4.15 and is predicted to be a cell-surface protein. The deduced amino acid sequence of dex showed homology to S. downei dextranase (63.9% identity). Phylogenetic analysis revealed the similarity of the deduced amino acid sequence of dextranases in S. criceti, S. sobrinus, and S. downei. A recombinant form of the protein with six histidine residues tagged in the C-terminus was partially purified and showed dextranase activity on blue-dextran sodium dodecyl sulfate-polyacrylamide gel electrophoresis (BD-SDSPAGE) followed by renaturation. We also detected dextranase activity in S. criceti cell extracts and culture supernatant by renatured BD-SDS-PAGE, whereas no dextranase activity of the cells was observed on blue-dextran brain heart infusion (BD-BHI) agar plates. Furthermore, PCR-based mutations of dextranase indicated that a deletion mutant of the C-terminal region could hydrolyze blue dextrans and that the D453E mutation, W793L mutation, and double mutations (W793L and deletion of the C-terminal region) resulted in a loss of dextranase activity. These findings suggest that Asp-453 and Trp-793 residues of S. criceti dextranase are critical to the enzyme's activity.

Overestimation of Streptococcus mutans prevalence by nested PCR detection of the 16S rRNA gene

This study was carried out in order to compare two PCR-based methods in the detection of Streptococcus mutans. The first PCR method was based on primers for the 16S rRNA gene and the second method was based on specific primers that targeted the glucosyltransferase gene (gtfB). Each PCR was performed with eight different streptococci from the viridans group, five other streptococci and 17 different non-streptococcal bacterial strains. Direct use of the S. mutans 16S rRNA gene-specific primers revealed that Streptococcus gordonii and Streptococcus infantis were also detected. After amplifying the 16S rRNA gene with universal primers and subsequently performing nested PCR, the S. mutans-specific nested primers based on the 16S rRNA gene detected all tested streptococci. There was no cross-reaction of the gtfB primers after direct PCR. Our results indicate that direct PCR and nested PCR based on 16S rRNA genes can reveal false-positive results for oral streptococci and lead to an overestimation of the prevalence of S. mutans with regards to its role as the most prevalent causative agent of dental caries.

First isolation ofStreptococcus downeifrom human dental plaques

In this study, we isolated four bacterial strains grown on mitis-salivarius sucrose bacitracin agar. The strains had similar biochemical characteristics to biotypes I or II of mutans streptococci. The four isolates were identified as Streptococcus downei by 16S rDNA and dextranase gene (dex) sequencing as well as polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) targeting dex. To our knowledge, this is the first report of the isolation and identification of S. downei from dental plaque in humans. The results suggest that S. downei can inhabit the human oral cavity.

Detection of cariogenic bacteria genes by a combination of allele-specific polymerase chain reactions and a novel bioluminescent pyrophosphate assay

We developed a novel bioluminescent assay for detection of pyrophosphate in polymerase chain reaction (PCR) product. The principle of this method is as follows: pyrophosphate released by PCR is converted to adenosine 5'-triphosphate (ATP) by pyruvate phosphate dikinase in the presence of the substrate pyruvate phosphate and the coenzyme adenosine 5'-monophosphate; subsequently, ATP concentration is determined by firefly luciferase reaction. The detection limit of pyrophosphate is 1.56 x 10(-15)mol/assay. Additionally, luminescent intensity reached a maximum at approximately 100 s and remained elevated beyond 10 min. This approach is applicable to the detection of cariogenic bacteria in dental plaque. Thus, the allele-specific PCR products of Streptococcus mutans and Streptococcus sobrinus developed in this study were measured via the proposed bioluminescent assay. This protocol, which does not require expensive equipment, can be utilized to rapidly monitor cariogenic bacteria in dental plaque.

Species-specific PCR method for identification of Streptococcus downei

AIMS

To establish a rapid method to differentiate Streptococcus downei and S. sobrinus by multiplex PCR.

METHODS AND RESULTS

A PCR primer pair specific to S. downei was designed on the basis of the nucleotide sequence of the dextranase gene of S. downei NCTC 11391T. The primer pair specifically detected S. downei, but none of the other mutans streptococci (16 strains of six species). The PCR procedure was capable of detecting 1 pg of genomic DNA purified from S. downei NCTC 11391 and as few as 14 CFU of S. downei cells. The mixture of primer pairs specific to each S. downei (this study) and S. sobrinus (Igarashi et al. 2000) detected only the strains of these two species among all the mutans streptococcal strains, and concomitantly differentiated the two species by species-specific amplicons of different lengths.

CONCLUSIONS

The present PCR method is highly specific to S. downei and is useful for detection and identification of S. downei.

SIGNIFICANCE AND IMPACT OF THE STUDY

Multiplex PCR using dextranase gene primers is a useful method for simultaneous detection and differentiation of S. downei and S. sobrinus.