Cariogenic Strains Of Streptococcus Mutans Research Articles

Effect of Lipoteichoic Acid Synthesis-Related Gene dltD on Acid Tolerance of Highly Cariogenic Strains of Streptococcus mutans

To study the role and possible mechanism of dltD in the acid tolerance of Streptococcus mutans 593 (SM593), and to provide a theoretical basis for the ecological prevention and control of dental caries by constructing the dltD gene deletion strain of SM593 (SM593-ΔdltD). 1) SM593-Δ dltD was constructed by homologous recombination. 2) The growth curve of SM593 dltD and SM593-Δ dltD under different pH culture conditions was drawn by the automatic growth curve analyzer to compare their acid tolerance. Colony forming unit (CFU) at different time points was used to calculate the survival rate and to compare the acid tolerance response (ATR) of SM593 and SM593-Δ dltD. 3) Under different pH conditions, glycolysis experiments, proton permeability test and H +-ATPase activity test were conducted to make preliminary exploration into the mechanisms of how dltD gene deletion may affect acid tolerance. 1) PCR and sequencing results showed that the SM593-Δ dltD was constructed successfully. 2) With decreasing pH value of the culture medium, the growth of SM593-Δ dltD slowed down. When the pH value of the culture medium was 5.0, SM593-Δ dltD was not allowed to grow, and its acid tolerance was lower than that of SM593. Compared with SM593, the ATR capability of SM593-Δ dltD was decreased. 3) SM593 dltD and SM593-Δ dltD did not show obvious difference in their glycolysis ability under different pH conditions. Compared with SM593 dltD, the proton permeability of SM593-Δ dltD under different pH conditions was increased significantly (P<0.05), and H +-ATPase activity decreased significantly (P<0.05). Compared with SM593 dltD, SM593-Δ dltD showed obvious decrease in acid tolerance, which may be caused by the significant increase in proton permeability and significant decrease in the H +-ATPase activity induced by the deletion of the dltD gene, hence reducing its ability to maintain intracellular pH homeostasis.

Cariogenicity and Acidogenicity of Human Milk, Plain and Sweetened Bovine Milk: An In Vitro Study

The objective of the present study was to determine the acidogenicity and cariogenicity of human breast milk and plain and sweetened packaged bovine milk. First all milk specimens were inoculated with a cariogenic strain of Streptococcus mutans (SM). The culture pH and number of colony forming units (cfus) was assessed. Second, the buffer capacity of all milk specimens was evaluated by mixing with acid. Finally, enamel windows were created on extracted primary maxillary incisors and colonized with SM. Enamel demineralization and caries progression were assessed visually, histologically, and radiographically at the end of twelve weeks. Plain and sweetened packaged bovine milk (BM) supported greater bacterial growth and caused more fermentation than human breast milk (HBM). The buffer capacity values for plain and sweetened bovine milk were highest; HBM, however had poor buffering capacity. The progression of the carious lesions into the dentin was most severe for the sweetened bovine milk. HBM and plain bovine milk are relatively cariogenic in an in vitro caries model in the absence of saliva. However, supplementation with sugar exponentially enhances the cariogenic potential of the natural milk.

Detection of potentially cariogenic strains of Streptococcus mutans using the polymerase chain reaction

Streptococcus mutans is a pathogen related to the occurrence of human dental caries. The determination of total amounts of mutans streptococci, as well as the proportion related to other oral bacteria, is of interest when assessing the risk of developing caries. In this context, it is better to use a sensitive, specific and non-time consuming method such as the polymerase chain reaction (PCR), than to use culture and biochemical identification methods. In this work we identified potentially cariogenic strains of S. mutans and assessed the relationship with the dmft, DMFT or dmft/DMFT index. Using DNA isolated from dental plaque, a 192 bp sequence was identified and amplified from the spaP gene and a 722 bp sequence from the dexA gene. The results suggest that it is important to evaluate the presence of cariogenic S. mutans strains in plaque content rather than the accumulation of plaque itself However, other factors like diet, hygiene, genetic background, the flow rate of saliva and the presence of specific antibodies, also play a key role in the development of caries.

The recombinant N-terminal region of human salivary mucin MG2 (MUC7) contains a binding domain for oral Streptococci and exhibits candidacidal activity

MG2 (the MUC7 gene product) is a low-molecular-mass mucin found in human submandibular/sublingual secretions. This mucin is believed to agglutinate a variety of microbes and thus is considered an important component of the non-immune host defence system in the oral cavity. We have shown that MUC7 can bind to cariogenic strains of Streptococcus mutans and that this binding requires a structural determinant in the N-terminal region. In the present study an expression construct, pNMuc7, encoding the N-terminal 144 amino acids of MUC7 was generated, and the recombinant protein rNMUC7 was expressed in Escherichia coli. Purified rNMUC7 was characterized and the binding of this protein to oral bacteria was investigated in an established assay. The results showed that the recombinant protein bound to S. mutans ATCC 25175 and ATCC 33402, and that alkylation of the two cysteine residues (Cys(45) and Cys(50)) resulted in the complete loss of bacterial binding. This suggests that binding of MUC7 to S. mutans occurs between the N-terminal region of the mucin molecule and the bacterial surface, and that this interaction is dependent on a cysteine-containing domain within this region of MUC7. In addition, the killing activity of rNMUC7 was compared with that of the candidacidal salivary protein histatin 5 in an established Candida albicans (ATCC 44505) blastoconidia killing assay. It was found that the LD(50) values of rNMUC7 and histatin 5 were comparable, and that the recombinant protein displayed significant killing activity at the physiological concentration range of MUC7 in whole saliva. This study is the first to show that the N-terminal region of MUC7 contains a structural determinant for bacterial binding and that this region exhibits candidacidal activity.

Effect of Anti-oxidants on Growth and Lactic Acid Production by Streptococcus mutans

The effects of three anti-oxidants--tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)--on both growth and lactic acid production by eight cariogenic strains of Streptococcus mutans were investigated. Synergistic inhibitory effects of potassium sorbate on lactic acid production were also determined. All three anti-oxidants are phenolic derivatives and are commonly used in food systems due to their excellent "carry-through" properties during processing. Growth inhibition was determined by turbidity measurements at 600 nm. Lactic acid was assayed by gas chromatography, and bacterial DNA was assayed by the diphenylamine reaction. There were reduced growth levels of S. mutans due to the anti-oxidants and potassium sorbate for at least 12 hr, with TBHQ and BHA still inhibiting growth at 24 hr. Nearly all concentrations of anti-oxidants and potassium sorbate reduced lactic acid production by S. mutans, but only TBHQ significantly inhibited lactic acid production when the amount of acid per microgram DNA was calculated. A synergistic reduction of lactic acid production by S. mutans does occur in most combinations of potassium sorbate with anti-oxidants.

Analysis of cell wall and membrane contamination of ribosomal preparations from Streptococcus mutans.

A ribosomal preparation from a cariogenic strain of Streptococcus mutans was examined for cell wall and membrane contamination. A biochemical characterization established that the preparation contained 61.0% RNA and 39.0% protein. Carbohydrate was not detected by phenol-sulfuric acid or methyl pentose assays. Glucosyltransferase and D-succinate dehydrogenase, which are cell wall- and membrane-associated enzymes, respectively, were not found. However, D-lactate dehydrogenase, another membrane-associated enzyme, was present in the preparation. A comparison of two-dimensional gel electropherograms of a mixture of cell walls and membranes and the S. mutans ribosomal preparation revealed contamination of the latter sample with at least six cell wall- or membrane-associated proteins. Adsorption of a rabbit antiserum raised against the ribosomal preparation with whole S. mutans cells abrogated antibodies directed against at least two proteins from the ribosomal preparation. Immunodiffusion plates showed reactivity of this antiserum against preparations of purified lipoteichoic acid from Streptococcus pyogenes and S. mutans. Adsorption of rat and rabbit antisera against the ribosomal preparation with the cell wall-derived materials glucosyltransferase, lipoteichoic acid, glucan, and a Rantz-Randall extract reduced the concentration of antibodies against the ribosomes by as much as 10-fold. These data indicated that the preparation was contaminated with at least six cell wall proteins, one cell membrane-associated enzyme, and lipoteichoic acid.

The interconversion of dextransucrase and mutansucrase activities from cariogenic strains of Streptococcus mutans

The interconversion of dextransucrase and mutansucrase activities from cariogenic strains of Streptococcus mutans

The interconversion of dextransucrase and mutansucrase activities from cariogenic strains ofStreptococcus mutans

The interconversion of dextransucrase and mutansucrase activities from cariogenic strains of<i>Streptococcus mutans</i>

Antibacterial Effect of Salivary Peroxidases on a Cariogenic Strain of Streptococcus mutans

The antibacterial effect of purified human salivary lactoperoxidase on a cariogenic strain of Streptococcus mutans was demonstrated while another oral peroxidase, probably of leukocytic origin, did not affect the growth. Lactoperoxidase was rapidly adsorbed by bacterial cells indicating the necessity of the contact between the enzyme and the cells before inhibition.

The Antibacterial Action of the Various Components of the Lactoperoxidase System on a Cariogenic Strain of Streptococcus mutans

Physiological activity of lactoperoxidase and in vivo concentration of thiocyanate ions were shown to be inhibitory against a cariogenic strain of Streptococcus mutans. However, the amount of H2O2 in vivo may be too low for optimum inhibition by lactoperoxidase system. H2O2 alone also inhibited the growth of S mutants to some degree.

Ingestion of Streptococcus mutans induces secretory immunoglobulin A and caries immunity.

Ingestion of killed cells of a highly cariogenic strain of Streptococcus mutans induced specific antibodies in both saliva and milk but not in serum of gnotobiotic rats. These antibodies were associated with the immunoglobulin A class. When infected with Streptococcus mutans, orally immunized animals developed significantly fewer carious lesions than nonimmunized infected controls.

The vitamin requirements of some oral streptococci

Of the 18 oral streptococci studied, 6 were cariogenic strains of Streptococcus mutans, while the other 12 were of unknown cariogenicity. All strains were grown aerobically and the vitamin requirements were determined by omitting in turn each of 8 B-group vitamins from a complete synthetic medium. Single transfer was used to show the non-essential nature of some of the vitamins. Pantothenate and nicotinic acid were essential or stimulatory for the growth of all strains but none required folic or p-amino-benzoic acids. The use of 2 other synthetic media suggested that the vitamin requirements of most strains were not influenced by the composition of the medium. With the possible exception of Streptococcus salivarius, the vitamin requirements do not indicate species or group divisions, nor do they appear to be related to cariogenicity. Moreover, these observations cannot account for the preferential colonization of various sites in the oral cavity by the streptococcal species.

Purification and characterization of a phosphatase specifically hydrolyzing p-nitrophenyl phosphate from an oral strain of Streptococcus mutans

A Mg-dependent phosphatase, specific for p-nitrophenyl phosphate, was purified 3000-fold from the cells of a cariogenic strain of Streptococcus mutans, using ion exchange chromatography and isoelectric focusing as the main steps. No heterogeneity in the enzyme molecules was observed in isoelectric focusing in a pH gradient from 4 to 6. Solubilization experiments supported the idea of a membrane-associated enzyme. The pI of the p-nitrophenyl phosphatase was 5.05 and its molecular weight was estimated to be approx 110,000. Of a large number of phosphate esters only p-nitrophenyl phosphate was hydrolyzed at a rate which could be measured reliably, indicating that the electron-attracting NO 2 group was necessary in the hydrolysis of the reactive species, which was considered to represent the monosubstituted dianion ( p-NO 2C 6H 4OPOs 3 2−). Optimum concentrations for the activating Mg 2+ and Co 2+ ions were 2.5 and 1.0 m m, respectively. Optimum pH for the hydrolysis of p-nitrophenyl phosphate was close to 8.0 at 30 °C. At this pH the substrate constant, K s , was 0.43 m m. Product inhibition was low. The several chemical reagents used and kinetic studies revealed no active serine residue or SH groups important in the action of the enzyme. Indirect evidence supports the idea of a rather “narrow” active centre where a specific NO 2 site was expected to occur.