Calcification of selected strains of Streptococcus mutans and Streptococcus sanguis

Physiological and genetic characterization of calcium phosphate precipitation by Pseudomonas species

Microbial biomineralization is a widespread phenomenon. The ability to induce calcium precipitation around bacterial cells has been reported in several Pseudomonas species but has not been thoroughly tested. We assayed 14 Pseudomonas strains representing five different species for the ability to precipitate calcium. Calcium phosphate precipitated adjacent to the colonies of all the Pseudomonas strains tested and also precipitated on the surface of colonies for several of the Pseudomonas strains assayed. The precipitate was commonly precipitated as amorphous calcium phosphate, however seven of the 14 Pseudomonas strains tested precipitated amorphous apatite in agar adjacent to the colonies. Out of the seven Pseudomonas strains that precipitated amorphous apatite, six are plant pathogenic. The formation of amorphous apatite was commonly observed in the area of the agar where amorphous calcium phosphate had previously formed. A transposon mutagenesis screen in Pseudomonas syringae pv. tomato DC3000 revealed genes involved in general metabolism, lipopolysaccharide and cell wall biogenesis, and in regulation of virulence play a role in calcium precipitation. These results shed light on the common ability of Pseudomonas species to perform calcium precipitation and the underlying genetic regulation involved in biomineralization.

Human dental plaque microcosm biofilms: effect of nutrient variation on calcium phosphate deposition and growth

Plaque mineralisation is a multi-factorial process involving plaque pH, nucleation, inhibitors and promotors. It is poorly understood because of its complexity.

OBJECTIVE

To establish the effects of amino acids and peptones in the simulated oral fluid BMM, a saliva analogue DMM and modifications of these on mineral deposition into dental plaque biofilm microcosms.

METHODS

Microcosms were cultured for up to 35 days in an Artificial Mouth pulsed with sucrose, followed by 10 days periodic treatment with a pH 5.0 calcium-phosphate-monofluorophosphate-urea solution (CPMU).

RESULTS

Initial biofilm doubling times were 3-7h, which then slowed and varied under the different nutrient conditions although their pH behaviour was similar. In BMM, mineral deposition was 20% that of DMM, but removal of BMM peptones increased deposition 12-fold. Substitution of the amino acids in DMM by casein did not affect deposition levels, but their removal leaving mucin the sole macronutrient, increased mineral deposition three-fold, reaching 40 mmol Ca/g protein.

CONCLUSIONS

These substantial increases in mineral deposition when the macronutrient concentration is reduced indicates probable changes in the nucleating, inhibitory and Ca-binding properties of the simulated oral fluids themselves and/or changes in the plaque microbiota and their crystal nucleators and inhibitors.

Calculus-like deposit on the apical external root surface of teeth with post-treatment apical periodontitis: report of two cases

AIM

To report two cases in which calculus-like material was found on external root surfaces of (i) an extracted root and (ii) an apicected part of a root, both of which were removed due to post-treatment refractory apical periodontitis.

SUMMARY

In each case, there was a fistulous tract, which did not heal after conventional root canal treatment. The first case did not heal even after apical surgery, and subsequent tooth extraction revealed calculus-like material on a root surface of complex anatomy. The second case showed radiographic signs of healing after apicectomy. Histology of the apical biopsy revealed a calculus-like material on the external surface of the root apex. It is suggested that the presence of calculus on the root surfaces of teeth with periapical lesions may contribute towards the aetiology of failure.

KEY LEARNING POINTS

Biofilm on the external root surface has been implicated in the failure of apical periodontitis to heal, despite adequate root canal treatment. Calculus-like material was found, in two cases, on the root surface of teeth with post-treatment apical periodontitis, where the only communication externally was a sinus tract.

Calcium phosphate deposition in human dental plaque microcosm biofilms induced by a ureolytic pH-rise procedure

The objectives were to develop and characterize a procedure based on a ureolytic pH rise to deposit calcium phosphate into microcosm dental plaque biofilms and to test the importance of the plaque pH range. Plaque biofilms were cultured in a multiplaque culture system ('artificial mouth') with a continuous supply of a simulated oral fluid (basal medium mucin; BMM) with 146 mmol/l (5% w/v) sucrose periodically applied over 6 min every 8h. After initial plaque growth, the biofilms were periodically exposed for up to 16 days to 6-min applications of calcium phosphate monofluorophosphate urea (CPMU) solution containing 20 mmol/l CaCl(2), 12 mmol/l NaH(2)PO(4), 5 mmol/l monofluorophosphate and 500 mmol/l urea (pH 5.0). Three application regimes were examined, one included a sucrose-induced acidic pH fluctuation. Plaque hydrolysis of the urea in CPMU caused the pH to rise to between 8.2 and 8.8, depositing fluoridated and carbonated calcium phosphates, and possibly some calcium carbonate, into the plaque. Calcium, phosphate and fluoride deposition was rapid for about 4 days and then slowed. After 10 days' treatment under standard conditions (BMM containing 1 mmol/l urea and 1 mmol/l arginine), plaque calcium and phosphate concentrations had increased up to 50-fold and 10-fold to approximately 2-4 and 1-2 mmol/g plaque protein, respectively. The calcium, phosphate and fluoride content increased steadily. Calcium phosphate deposition was proportional to the plaque resting pH, increasing over four-fold when the BMM urea concentration was increased from 0 to 20 mmol/l, which raised the resting pH from 6.4 to 7.2 and yielded a mean plaque calcium concentration of 14.3 mmol/g protein, one subsample reaching 20.8 mmol/g protein. Supplementation of BMM with 20% human serum inhibited deposition. These results support the hypothesis that an alkaline pH in plaque is critical in promoting plaque mineralization and that mineral deposition is modulated by serum. These factors are likely to be important in regulating calculus formation.

Inhibition of nanobacteria by antimicrobial drugs as measured by a modified microdilution method

Compounds from 16 classes of antimicrobial drugs were tested for their abilities to inhibit the in vitro multiplication of nanobacteria (NB), a newly discovered infectious agent found in human kidney stones and kidney cyst fluids from patients with polycystic kidney disease (PKD). Because NB form surface calcifications at physiologic levels of calcium and phosphate, they have been hypothesized to mediate the formation of tissue calcifications. We describe a modified microdilution inhibitory test that accommodates the unique growth conditions and long multiplication times of NB. This modified microdilution method included inoculation of 96-well plates and determination of inhibition by periodic measurement of the absorbance for 14 days in cell culture medium under cell culture conditions. Bactericidal or bacteriostatic drug effects were distinguished by subsequent subculture in drug-free media and monitoring for increasing absorbance. NB isolated from fetal bovine serum (FBS) were inhibited by tetracycline HCl, nitrofurantoin, trimethoprim, trimethoprim-sulfamethoxazole, and ampicillin at levels achievable in serum and urine; all drugs except ampicillin were cidal. Tetracycline also inhibited multiplication of isolates of NB from human kidney stones and kidney cyst fluids from patients with PKD. The other antibiotics tested against FBS-derived NB either had no effect or exhibited an inhibitory concentration above clinically achievable levels; the aminoglycosides and vancomycin were bacteriostatic. Antibiotic-induced morphological changes to NB were observed by electron microscopy. Bisphosphonates, aminocaproic acid, potassium citrate-citric acid solutions, and 5-fluorouracil also inhibited the multiplication of NB in a cidal manner. Insights into the nature of NB, the action(s) of these drugs, and the role of NB in calcifying diseases may be gained by exploiting this in vitro inhibition test system.

Microbiota of periapical lesions refractory to endodontic therapy

The periapical microbiota of 36 teeth with refractory apical periodontitis was investigated. None of the teeth had responded to conventional endodontic or long-term (> 6 months), calcium-hydroxide treatment. Eight patients had received antibiotics systemically. After anaerobic culture, a total of 148 microbial strains were detected among 67 microbial species. One of the 36 lesions was culture-negative. Approximately half (51.0%) of the bacterial strains were anaerobic. Gram-positive species constituted 79.5% of the flora. Facultative organisms, such as Staphylococcus, Enterococcus, Enterobacter, Pseudomonas, Stenotrophomonas, Sphingomonas, Bacillus, or Candida species were recovered from 27 of the lesions (75%). Sulfur granules were found in 9 lesions (25%). In these granules Actinomyces israelii, A. viscosus, A. naeslundii, and A. meyeri were identified. Other bacterial species, both gram-positive and gram-negative, were detected in the granules as well. Two sulfur granules did not contain Actinomyces. Scanning electron microscopy demonstrated rod- and spirochete-like cells in the granules, and transmission electron microscopy revealed organisms with copious amounts of extracellular material. Outer membrane vesicles were also seen. Some of the granules were calcified. This study demonstrated a wide variety of microorganisms, particularly gram-positive ones, in the periapical lesions of teeth with refractory apical periodontitis.

Mineralization of Streptococcus mutans in vitro. An ultrastructural study

Streptococcus mutans mineralization was studied in vitro, with the use of various metastable calcium phosphate solutions, fluoride-containing or otherwise. Degeneration of bacteria always occurred before their mineralization. After complete mineralization of the cytoplasmic area, growth of crystals was observed both in length and in thickness within the extracellular environment. Composition of the calcifying medium was an essential factor in the S. mutans mineralization process. The present study shows that, contrary to carbonate and magnesium ions that prevent intra- and extracellular deposits, fluoride ions promote crystal growth in the above mentioned mediums. Clinical implications of the role of fluoride, at the plaque level, are foreseen.

Calcification of a cariogenic Streptococcus and of Corynebacterium (Bacterionema) matruchotii

The main aim of this investigation was to challenge the idea that cariogenic streptococci do not calcify. Calcium uptake of calcification of Streptococcus mutans C180-2, proven to be an acidogenic and cariogenic strain, was compared with calcium uptake and calcification of Corynebacterium (Bacterionema) matruchotii, known as a ready calcifier. Bacteria were grown on Brain Heart Infusion Agar (BHIA) and on well-buffered semi-synthetic E-agar, both containing 1.4 mmol/L calcium, 2 g/L glucose, initial pH 7.4. Calcium uptake from BHIA by C. matruchotii (25 mmol Ca/kg wet bacterial cell mass), but not by S. mutans, was found. Grown as a plaque-like lawn on E-agar, the S. mutans cell mass concentrated calcium to 63 +/- 11 mmol/kg compared with 145 +/- 61 mmol/kg in C. matruchotii. X-ray diffraction confirmed the presence of crystalline apatite in the bacterial cell masses. Electron microscopy revealed crystals and mineralized deposits in both organisms. Heavy calcifications in some cells of S. mutans were seen. Calcification was partly inhibited by magnesium ion and by methanehydroxybisphosphonate. S. sobrinus 6715, as well as freshly isolated S. mutans and S. sobrinus from patients, concentrated very large quantities of calcium, up to 500-fold from the medium, when maintained for several weeks on E-agar of initial pH 7.6. Our observations widen the view on acidogenic bacteria as mineralization agents and support the notion that members of the mutans group of streptococci may be involved in events that trigger heavy intracellular calcifications and, possibly, dental calculus formation.

Silica-induced precipitation of calcium phosphate in the presence of inhibitors of hydroxyapatite formation

The promotion and the inhibition of hydroxyapatite formation by various substances were determined by measurement of the induction time of spontaneous precipitation (ti) from supersaturated solutions. Silica was found to decrease ti in Hepes-buffered (pH 7.2) supersaturated solutions with a wide range of calcium-to-phosphate ratios and concentrations. Also, in suspensions of the oral bacteria S. mutans or C. matruchotii in 1 mmol/L calcium, 7.5 mmol/L phosphate, and 50 mmol/L Hepes (pH 7.2), silica was capable of stimulating precipitation. Macromolecules derived from these bacteria by freezing and thawing appeared to be strong inhibitors of calcium phosphate precipitation. In the presence of silica, the effects of these bacterial inhibitors could be partially overcome, which supports the idea that silica in dental plaque is a promoter of calculus formation. In contrast, inhibition of calcium phosphate precipitation by a low-molecular-weight inhibitor, pyrophosphate, could not be counteracted by silica.

Characterization of calcifiable proteolipid from Streptococcus mutans

Proteolipid is known to initiate calcification in vitro. Apoprotein and phospholipid components of proteolipid from five of 14 calcifiable S. mutans specimens were characterized. The apoproteins contained 16 amino acids with calculated percent polarities ranging from 32.0 to 45.2. The acidic phospholipids were cardiolipin, mono- and diphosphoinositides, and phosphatidylserine. Neutral lipids, phosphatidylethanolamine and phosphatidylcholine, were also found. The latter were the most abundant in all isolates. Appropriate hydrophobic proteins and acidic phospholipids in the proteolipids accounted for S. mutans calcifiability.

Calcifiability comparison among selected microorganisms

Seven ATCC strains of bacteria were examined for apatite formation in a chemically-defined calcification-supporting medium and also in a metastable calcium phosphate solution. One, E. coli, calcified in both. One, S. aureus, calcified in the solution, but not in the medium. The other five did not calcify in either. The results substantiate the belief that calcification is restricted to certain microorganisms. However, they do not rule out the possibility that a noncalcifiable microorganism has the potential to calcify, and the activity is prevented by a cell component. Additionally, the findings emphasize that determining microbiologic calcifiability only in a calcification-supporting culture medium is inadequate. In culture, an efficient calcium pump might preclude calcification by establishing a cytoplasmic calcium level too low for nucleation activation. Calcifiability assays should be done by incubating minimally-metabolizing freeze-dried cells in metastable calcium phosphate solution.

Biology, immunology, and cariogenicity of Streptococcus mutans

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Evolutionary prerequisites for early Phanerozoic calcareous skeletons

This paper develops the concept that the dramatic appearance of calcareous skeletons in the Lower Cambrian is directly related to the origin of refined mechanisms of intracellular modulation of calcium ion concentration. An homologous family of calcium modulated proteins has recently been discovered. These proteins contain "EF hands", involved in the maintenance of low concentrations of intracellular calcium and the informational use of calcium ion flow (Kretsinger, 1977). The evolution of this specialized calcium physiology, especially in muscle systems, coupled with natural selection by predators are identified as some of the preadaptations for the impressive Tommotian diversification of calcified metazoans. The distribution of calcium biominerals in the phyla of the five kingdoms and the time of first appearance of calcareous mineralization in the fossil record are tabulated. Macroscopic calcified hard parts apparently required the prior evolution of certain cell, tissue and organ system physiologies which are briefly discussed here.

Extracellular dextran hydrolase from Streptococcus mutans strain 6715

Streptococcus mutans strain 6715 was shown to produce an extracellular dextramase with endohydrolytic alpha-(1 leads to 6)-glucan-6-glucanohydrolase activity. The enzyme degraded soluble polymers produced by some oral streptococci but did not disperse the streptococcal plaques tested. Enzyme levels in the culture supernatant were elevated in sucrose and sucrose plus glucose cultures but remained at basal levels in glucose and dextran plus glucose cultures.

Calcification by Candida albicans

Candida albicans was grown in a chamically defined medium in which certain microorganisms are known to calcify. The fungus developed calcium phosphate deposits with the same X-ray diffraction maxima as biological apatite.