Rapid isolation of chromosomal DNA from oral streptococci and polymerase chain reaction-oriented restriction fragment-length polymorphism analysis for genetic heterogeneity

Longitudinal study of dental caries incidence associated with Streptococcus mutans and Streptococcus sobrinus in patients with intellectual disabilities

Background

Mutans streptococci (Streptococcus mutans and S. sobrinus) are considered to be major etiologic agents of dental caries. Using a polymerase chain reaction method, we detected those bacteria from 145 outpatients (6–30 years old) with intellectual disabilities (ID) and their presence was compared with the incidence of dental caries.

Methods

Plaque samples were collected from all erupted tooth sites in subjects with a sterile toothbrush. A dental examination was performed to determine the number of decayed and filled teeth (DFT score) in permanent dentition using the WHO caries diagnostic criteria. A Mann–Whitney U-test was employed to compare the caries scores between combinations of the bacteria, and with a Wilcoxon rank test used to compare caries scores between the baseline and after 1 year.

Results

Among all subjects, S. mutans and S. sobrinus were possessed by 78.7 and 83.5 %, respectively, while 13.1 % were positive for S. mutans alone, 17.9 % for S. sobrinus alone, and 65.6 % for both organisms, with 3.4 % were negative for both. The mean DFT score of subjects positive for both S. mutans and S. sobrinus at after 1 year was significantly higher than that of those positive for S. mutans alone (P < 0.01). The increase in caries increment was also significantly greater in subjects with both bacteria detected (P < 0.001).

Conclusion

Our results indicate that patients with ID harboring both S. mutans and S. sobrinus have a significantly higher incidence of dental caries than those with S. mutans alone.

Streptococcus oriloxodontae sp. nov., isolated from the oral cavities of elephants

Two strains were isolated from oral cavity samples of healthy elephants. The isolates were Gram-positive, catalase-negative, coccus-shaped organisms that were tentatively identified as a streptococcal species based on the results of biochemical tests. Comparative 16S rRNA gene sequence analysis suggested classification of these organisms in the genus Streptococcus with Streptococcus criceti ATCC 19642T and Streptococcus orisuis NUM 1001T as their closest phylogenetic neighbours with 98.2 and 96.9 % gene sequence similarity, respectively. When multi-locus sequence analysis using four housekeeping genes, groEL, rpoB, gyrB and sodA, was carried out, similarity of concatenated sequences of the four housekeeping genes from the new isolates and Streptococcus mutans was 89.7 %. DNA–DNA hybridization experiments suggested that the new isolates were distinct from S. criceti and other species of the genus Streptococcus . On the basis of genotypic and phenotypic differences, it is proposed that the novel isolates are classified in the genus Streptococcus as representatives of Streptococcus oriloxodontae sp. nov. The type strain of S. oriloxodontae is NUM 2101T ( = JCM 19285T = DSM 27377T).

Streptococcus mutans and Streptococcus sobrinus detection by Polymerase Chain Reaction and their relation to dental caries in 12 and 15 year-old schoolchildren in Valencia (Spain)

A cross-sectional study was carried out to determine the prevalence of Streptococcus mutans and Streptococcus sobrinus and the association of the two in a random sample (n=614) of the child population of the region of Valencia (Spain). Saliva samples were analyzed by the quantitative polymerase chain reaction (PCR) method to study the relation of these bacteria to caries prevalence and the DMFT index. The prevalence of S. mutans was 35.4% at age 12 and 22.9% at age 15, that of S. sobrinus 18.9% and 8.4% and that of the S. mutans-S. sobrinus association 18.2% and 6.8% respectively. At both 12 and 15 years of age, the caries prevalence rates were lower in the Streptococcus-free group of children (37.6% and 48.5% respectively) and higher in the S.mutans-only group (67.3% and 74.0%). At the age of 12, the DMFT index was significantly higher in the mutans-only carriers (2.1) than in the Streptococcus-free and S. mutans-S. sobrinus association groups (both 0.9). At the age of 15, the DMFT index was significantly higher in the S. mutans-S. sobrinus association (3.71) and mutans-only (3.1) carrier groups than in the Streptococcus-free group (1.4). Determination of S. mutans and S. sobrinus by real-time quantitative PCR can provide valuable information for caries risk assessment in epidemiological studies.

Key words:Streptococcus mutans, Streptococcus sobrinus, polymerase chain reaction, dental caries, cross-sectional studies.

Sequence and phylogenetic analyses of the water-soluble glucan synthesizing-glucosyltransferase genes of Streptococcus dentirousetti

Two tandemly aligned glucosyltransferase (GTF) genes whose gene products are responsible for water-soluble glucan synthesis were isolated from Streptococcus dentirousetti NUM1303 and sequenced. One of the GTF genes of S. dentirousetti consisted of a 4110 bp open reading frame (ORF) that encoded for a 1369 amino acid protein and was revealed to be a S. sobrinus gtfS homolog. The percent similarity of amino acid sequences of the GTF-S from S. dentirousetti compared to those from S. sobrinus was 99%. In addition, a putative gtfT was found in tandem in the downstream region of the S. dentirousetti gtfS. The gtfT of S. dentirousetti consisted of a 4527 bp ORF encoding for 1508 amino acids. The similarity of amino acid sequences of the GTF-T from S. dentirousetti and S. sobrinus was 94%. Phylogenetic analysis based on amino acid sequences from other related streptococcal GTFs suggested that both GTF-S and GTF-T of S. dentirousetti are closely related to S. sobrinus.

Caries prevalence associated with Streptococcus mutans and Streptococcus sobrinus in Japanese schoolchildren

BACKGROUND

Streptococcus mutans and Streptococcus sobrinus are known to be associated with dental caries in humans.

AIM

We used a polymerase chain reaction method to detect S. mutans and S. sobrinus in 128 Japanese schoolchildren and then compared their presence with the dental caries experience.

DESIGN

Plaque samples were collected from all erupted tooth sites with a sterile toothbrush, and dental examinations were performed to determine the numbers of decayed and filled teeth in primary (dft) and permanent (DFT) dentition using the WHO caries diagnostic criteria. Fisher's PLSD test was employed to compare caries scores between combinations of the detected bacteria.

RESULTS

Streptococcus mutans and S. sobrinus were present in 38.3% and 68.0%, respectively, whereas 14.8% were positive for S. mutans alone, 44.5% for S. sobrinus alone, and 23.5% for both S. mutans and S. sobrinus, with 17.2% negative for both. The DFT, dft, and total (DFT + dft) scores for subjects positive for both S. mutans and S. sobrinus were significantly higher than those positive for S. mutans alone (P < 0.05, in triplicate).

CONCLUSION

These results suggest that schoolchildren harbouring both S. mutans and S. sobrinus have a significant higher dental caries experience in both permanent and primary teeth as compared to those with S. mutans alone.

Streptococcus ursoris sp. nov., isolated from the oral cavities of bears

Three Gram-positive, catalase-negative, coccus-shaped organisms were isolated from the oral cavities of bears. The isolates were tentatively identified as a streptococcal species based on the results of biochemical tests. Comparative 16S rRNA gene sequencing studies confirmed that the organisms were members of the genus Streptococcus, but they did not correspond to any recognized species of the genus. The nearest phylogenetic relative of the new isolates was Streptococcus ratti ATCC 19645T (98.6 %), however, DNA–DNA hybridization analysis showed that the isolates displayed less than 15 % DNA–DNA relatedness with the type strain of S. ratti. Colonies of the novel strains grown on mitis salivarius agar showed an extracellular polysaccharide-producing colony morphology. Based on phenotypic and phylogenetic evidence, it is proposed that the novel isolates are classified in the genus Streptococcus as Streptococcus ursoris sp. nov. The type strain of S. ursoris is NUM 1615T (=JCM 16316T=DSM 22768T).

Late Established Mutans Streptococci in Children over 3 Years Old

Acquisition of mutans streptococci has been reported to most commonly occur at approximately 26 months of age. In the present study, we detected Streptococcus mutans and S. sobrinus using polymerase chain reaction (PCR) assays in children, then re-examined the subjects to determine the time of acquisition of these bacteria over a 1-year period. The subjects were 57 children ranging in age from 3 to 5 years old, each with primary dentition. Plaque samples were collected from all erupted tooth sites using a sterile toothbrush. PCR assays were performed to detect the targeted mutans streptococci at the beginning of the study (baseline) and after 1 year. At the baseline examination, the prevalence of S. mutans and S. sobrinus was 61.4% and 54.4%, respectively, in all subjects, of whom 14 (24.6%) were positive for S. mutans alone, 10 (17.5%) for S. sobrinus alone, and 21 (36.8%) for both S. mutans and S. sobrinus, with 12 (21.1%) negative for both. After 1 year, 4 of 22 (18.2%) subjects newly had acquired S. mutans and 15 of 26 (57.7%) had aquired S. sobrinus, while 5 (8.8%) remained negative for both bacteria. The age of the first positive S. mutans finding ranged from 49 to 71 months, while that for S. sobrinus ranged from 49 to 81 months old. Our results suggest that S. sobrinus becomes established later than S. mutans in the oral cavities of children over the age of 3 years old.

Development of species-specific primers for detection of Streptococcus mutans in mixed bacterial samples

Streptococcus mutans is the major microbial pathogen associated with dental caries in children. The objectives of this study were to design and evaluate species-specific primers for the identification of S. mutans. Validation of the best primer set, Sm479F/R, was performed using seven S. mutans reference strains, 48 ATCC non-S. mutans strains, 92 S. mutans clinical isolates, DNA samples of S. mutans-Streptococcus sobrinus or S. mutans-Streptococcus sanguinis, and mixed bacterial DNA of saliva samples from 33 18-month-old children. All of the S. mutans samples tested positive, and no PCR products were amplified from members of the other streptococci or nonstreptococci strains examined. The lowest detection level for PCR was 10(-2) ng of S. mutans DNA (c. 4.6 x 10(3) copies) in the test samples. The results of this study suggest that the Sm479F/R primer pair is highly specific and sensitive for identification of S. mutans in either purified or mixed DNA samples.

Evaluation of microbial RNA extractions from Streptococcus pneumoniae

The mechanisms that control Streptococcus pneumoniae's ability to colonize the nasopharynx or to invade the middle ear and cause acute otitis media are not understood. Focused study of these mechanisms requires efficient methods for the extraction of microbial RNA from minute clinical samples. Several lysis/extraction methods were tested and compared to determine the optimal conditions for isolating intact total RNA from pneumococcal cells. The sensitivity and efficiency of the extractions were evaluated by reverse transcription polymerase chain reaction (RT-PCR). Compared to other methods, mechanical homogenization in TRIZOL was the most efficient for releasing microbial RNA, and addition of polyinosinic acid (Poly I) as an RNA carrier increased the assay sensitivity to 10(2) colony forming units when detected by RT-PCR amplification of 16S ribosomal RNA or messenger RNA for penicillin binding protein 2b. Quantitative results were confirmed using a ribonuclease protection assay. Penicillin binding protein 2b was also detected in rat middle ear mucosa recovered 5 weeks after middle ear challenge with S. pneumoniae. This study describes a useful core methodology for use in identifying pneumococcal virulence genes from small titer samples and has promising applications in clinical studies of pneumococcal nasopharyngeal colonization and otitis media pathogenesis.

In vitro growth and acid production by mutans streptococci on traditional African foods

The growth rate and production of acids by mutans streptococci (MS) are influenced by their ability to ferment different dietary carbohydrates. This suggests that the nutrient environment in the oral cavity affects bacterial virulence. The aim of this study was to investigate the effect of maize, samp and brown bread on the growth and acidogenicity of this species. Six laboratory references and five clinical strains isolated from the dental plaque of South African black and 'colored' (historical race classification) children were studied in batch culture on maize, samp (coarsely ground maize), brown bread and compared against a 3% sucrose control. The doubling time of bacterial strains was prolonged in maize (1.9-17.5 h) and samp (2.4-18.4 h), and the number of cell divisions was low. Staple foods accounted for 25% (F=5.98; P=0.0007) and MS strains 30.78% (F=2.84; P=0.009) of the total variance. The fermentation of samp and maize showed the least drop in pH of the culture medium, ranging between 0.54 and 1.06 and 0.69 and 2.28 pH units respectively, with variation between strains most significant in maize (F=33.62; P<0.0001). The total mean concentration of acids produced was highest in bread (25.13 mM/mL) and samp (17.00 mM/mL) which was comparable to Brain Heart Infusion broth (16.49 mM/mL) and a basal synthetic medium (17.96 mM/mL) containing 3% sucrose, but the yield of lactate, acetate and formate was low during the fermentation of samp (0.50 mM/mL), BHI+3% sucrose (4.12 mM/mL) and brown bread (0.06 mM/mL) respectively. Results indicated that maize and samp do not optimally support the growth or acid production by MS, and the varying response of test strains demonstrates the strain variability of this species to different carbohydrate sources in the diet.

Characterization of Streptococcus mutans diversity by determining restriction fragment-length polymorphisms of the gtfB gene of isolates from 5-year-old children and their mothers

The diversity between Streptococcus mutans clinical isolates from 5-year-old children and their mothers in two South African ethnic groups was investigated. The gtfB gene encoding for glucosyltransferase (EC 2.4.1.5), an enzyme responsible for the synthesis of extracellular polysaccharides was characterized by PCR-RFLP with HaeIII restriction enzyme digestion. Forty-seven children were examined for dental caries and 128 S. mutans clinical isolates cultured from samples of their saliva and plaque and from the saliva of their mothers. Thirty-three children had active caries (70%) and the remainder (n = 14) were caries-free. Caries prevalence was significantly different (p = 0.02) between black African and coloured children, but no differences were found between gtfB amplitypes by caries or ethnic grouping. Thirty-four (27%) of the S. mutans clinical isolates investigated did not ferment melibiose. Melibiose-negative phenotypes (n = 10) isolated from four families showed gtfB RFLP patterns identical to each other. Mothers and children harboured between one and three amplitypes. GtfB amplitypes were identical in 17 families (17/47), of which nine only were identical to S. mutans reference strains. The percentage match between S. mutans amplitype from mothers and their children was low (13%) in the caries-free group compared to children with caries (44%). RFLP analysis of the gtfB gene showed the diversity of S. mutans genotypes within two South African populations that were acquired from mothers and other sources.

Longitudinal study of dental caries incidence associated with Streptococcus mutans and Streptococcus sobrinus in pre-school children

Streptococcus mutans and Streptococcus sobrinus are known to be associated with the development of dental caries. In this study these bacteria were detected in pre-school children (each with primary dentition, age range 3-5 years, n = 60) using a PCR method, and then their presence was compared with the incidence of dental caries over a 1-year period. Plaque samples were collected from all erupted tooth sites using a sterile toothbrush. Dental examinations at the beginning of the study (baseline) and after 1 year were also performed to determine decayed, missing, filled teeth (dmft) scores using WHO caries diagnostic criteria. The prevalences of S. mutans and S. sobrinus across all the subjects were 61.7% and 56.6%, respectively; 13 subjects (21.7%) were positive for S. mutans alone, 10 (16.6%) were positive for S. sobrinus alone and 24 (40.0%) were positive for both S. mutans and S. sobrinus, whereas 13 (21.7%) were negative for both S. mutans and S. sobrinus. dmft scores of subjects positive for both S. mutans and S. sobrinus at baseline and after 1 year were significantly higher than of those positive for S. mutans alone at the same stages (P < 0.01 and P < 0.001, respectively). The caries incremental increase was also significantly greater in those with both bacteria detected (P < 0.05). Our results indicate that pre-school children harbouring both S. mutans and S. sobrinus have a significantly higher incidence of dental caries than those with S. mutans alone.

Expression of the gtfI gene from Streptococcus sobrinus in Streptococcus anginosus using integration-mediated transformation system

We have constructed a Streptococcus anginosus transformant expressing the gtfI gene from Streptococcus sobrinus, using a previously developed integration-mediated transformation system to introduce foreign genes onto the oral streptococcal chromosome, and attempted to evaluate the gene expression. In this system, one cloning plasmid and three pACYC184 derivatives, anchor, heterodimer, and integration plasmids were used for the construction of a series of integrants via homologous recombination. A portion of S. sobrinus gtfI gene devoid of approximately 1 kb of the 5'-region derived from pMD39 was cloned into the integration plasmid and introduced onto the S. anginosus chromosome. Next, the polymerase chain reaction product corresponding to 2.0 kb of the 5'-region of the gtfI gene from S. sobrinus chromosome was further cloned into the cloning plasmid, and the intact gtfI gene was reconstructed following integration. The final S. anginosus integrant successfully secreted the enzymatically active gtfI gene products and extracellular enzyme was characterized. This enzyme produced water-insoluble glucans and glucan-forming activity was stimulated by the addition of dextranT10. When this integrant was grown in Todd-Hewitt broth supplemented with sucrose, the integrant adhered to the glass surface in vitro and this integrant exhibited the different colony morphology on Mitis-Salivarius agar plates compared to S. sobrinus and S. anginosus. These observations strongly suggest that the construction of S. anginosus integrant expressing S. sobrinus gtfI gene using this transformation system may be an effective means of analysis of cariogenic biofilm formation.

Determination of mutacin activity and detection of mutA genes in Streptococcus mutans genotypes from caries-free and caries-active children

Relationships between genetic diversity, mutacin production and sensitivity to mutacins in Streptococcus mutans were evaluated in 19 clinical isolates from caries-free and caries-active children. Mutacin production was tested against 30 indicator strains; results showed significant variations in the inhibitory spectra of the clinical isolates. There was no association between the inhibitory spectrum of the infecting strain and the caries experience or the level of mutans streptococci infection of the host. Homology to the mutA gene coding for mutacin II was detected in one clinical isolate; none of the clinical isolates showed homology to the mutA genes coding for mutacins I or III. Genotyping by random amplified polymorphic DNA (RAPD) reactions grouped the isolates into three clusters, but no correlation was found between any of the clusters and mutacin activity, caries experience or level of mutans streptococci in the host.

Diversity of Streptococcus mutans bacteriocins as confirmed by DNA analysis using specific molecular probes

Mutacin-producing strains have been classified into 24 groups (designated by letters A to X) by similarity in activity spectra and cross-immunity. Similarity in primary structure among these groups can be revealed using DNA hybridization. The amino acid sequences of four mutacins (B-Ny266, 1140/mutacin III and mutacin II) were used to design two DNA probes in order to detect similar genes among groups of Streptococcus mutans strains demonstrating inhibitory activity. In addition to the appropriate parent strain, each probe hybridized with the total DNA from only two out of the 24 mutacin group type strains. Thus, the remaining 18 groups of strains produce mutacins that differ from the mutacins sequenced to date. In order to explore the similarity between genes coding for mutacins B-Ny266 and JH1140, the group B specific probe was utilized to detect a DNA fragment of 1.9 kb in the genome of S. mutans strain Ny266. The sequence of the cloned fragment codes for three open reading frames (lanA, lanA' and lanB) similar to those of strains JH1140 and UA787. The gene lanA' is strongly similar to the structural gene lanA (67%), but only one RNA transcript of about 300 bases was detected by Northern hybridization using the lanA-lanA' probe. Transcription of lanA alone was verified by RT-PCR.

Simple and rapid detection of Streptococcus mutans and Streptococcus sobrinus in human saliva by polymerase chain reaction

Streptococcus mutans and Streptococcus sobrinus are major pathogens causing dental caries in humans. A simple and rapid method to detect these species in human saliva simultaneously was developed using the polymerase chain reaction (PCR). Chromosomal DNA was extracted by boiling bacterial cells in lysis solution containing 1% Triton X-100. Oligonucleotide primers specific for portions of the glucosyltransferase genes (gtfB of S. mutans and gtfI of S. sobrinus) were designed. After PCR using two sets of these primers, S. mutans and S. sobrinus were specifically identified. The method was capable of amplifying DNA fragments specific for these species from chromosomal DNA extracted from 1 x 10(3) cells, or from 10 microliters of clinical saliva samples containing 1 x 10(3) colony-forming units of either streptococcal species. A second PCR, using the first PCR product as a template with newly designed internal primers, made it possible to detect 1 x 10(2) colony-forming units of either streptococcal species in 10 microliters of saliva samples. These results indicate that the PCR method developed in this study is useful for detecting S. mutans and S. sobrinus in saliva and that it can be used in epidemiological studies to evaluate the prevalence level of these organisms.