Isolation and immunobiological classification of Streptococcus sanguis from human tooth surfaces

Growth Inhibitory Effects of Antimicrobial Natural Products against Cariogenic and Health-Associated Oral Bacterial Species

PURPOSE

This study investigated whether selected natural products could specifically target the growth of a caries-associated bacterial species (Streptococcus mutans) without affecting the viability of a health-associated oral commensal bacterial species (Streptococcus sanguinis).

MATERIALS AND METHODS

Agar diffusion assays were used to screen the natural products for bacterial-growth inhibitory effects and the diameters of the inhibitory zones for the two bacterial species compared. The minimum inhibitory concentrations (MIC) of the natural products that showed growth inhibitory effects were determined using the broth microdilution method.

RESULTS

Except for the berry extracts (cranberry, wild blueberry, and strawberry), all the other selected natural products (peppermint, ginger, cinnamon, rosemary, liquorice, xanthorrrhizol, tt-farnesol, guaijaverin, and macelignan) exhibited varying degrees of bacterial growth inhibition. The MIC values ranged from as low as 4 µg/ml for xanthorrrhizol to 1000 µg/ml for guaijaverin. All the growth inhibitory natural agents tested showed similar inhibition for both S. mutans and S. sanguinis.

CONCLUSIONS

Although several natural products exerted significant antibacterial effects, none had selective inhibitory action on the growth of S. mutans.

Inhibitory effects of children's toothpastes on Streptococcus mutans, Streptococcus sanguinis and Lactobacillus acidophilus

AIM

As suppression of Streptococcus mutans in young children may prevent or delay colonisation of the oral cavity, toothbrushing with dentifrices containing anti-S. mutans activity may aid in preventing caries. The aims of this study were to compare the effects of children's dentifrices on the growth of S. mutans and non-mutans bacteria (Streptococcus sanguinis and Lactobacillus acidophilus).

MATERIALS AND METHODS

The agar diffusion assay at neutral pH was used to examine the antibacterial activity of commercial dentifrices and their major constituents.

RESULTS

Dentifrices containing 1,450 ppm fluoride produced greater growth inhibition of both S. mutans and S. sanguinis than those with <500 ppm. No inhibition was seen for pure solutions of sodium fluoride or sodium monofluorophosphate at fluoride concentrations up to 100,000 ppm. Stannous fluoride exerted antibacterial effects at concentrations above 10,000 ppm. Significant growth inhibition of both S. mutans and S. sanguinis was seen with sodium lauryl sulphate at 2,500 ppm and with triclosan at 100 ppm. No inhibitory effects were seen for xylitol, sorbitol, sodium pyrophosphate or polyethylene glycol at concentrations up to 80,000 ppm.

CONCLUSION

Sodium lauryl sulphate is the major bacterial inhibitory compound in children's dentifrices.

Identification and classification of species within the Streptococcus sanguis group

A biochemical identification scheme has been produced that allows for the differentiation of nine distinct species within the Streptococcus sanguis group. The species are S. sanguis, S. gordonii, S. crista, S. oralis, S. parasanguis, S. defectivus, S. adjacens and S. mitis, which have been previously described, and a new species, S. australis; in addition two distinct subspecies, S. oralis subsp. corona and S. oralis subsp. mitior, have been identified. DNA-DNA hybridization confirmed the separation of strains into the species. A new type of peptidoglycan peptide linkage, lys-ala-gly was also found within the species S. parasanguis and S. australis that has not been observed within the streptococci previously. DNA fingerprinting was shown to be a useful method for discriminating between strains within species, but did not allow discrimination between species.

Multiple phase variation in haemolytic, adhesive and antigenic properties of Streptococcus gordonii

Streptococcus gordonii gave rise to beta-haemolytic variants (Bhp+ for beta-haemolysin production) at frequencies of 10(-4)-10(-3) on agar medium containing washed horse erythrocytes. Bhp+ variants reverted to the wild-type alpha-haemolytic phenotype (Bhp-) at the same frequencies. There was a significant probability (> or = 0.1) that phase variation in Bhp and phase variation in the previously described Spp (sucrose promoted phenotype) would occur concomitantly, but there was no correlation between these phenotypes. There was evidence also of independent phase variation in adhesion to saliva-coated hydroxyapatite (Asp for adhesion to salivary pellicles), in lactose-sensitive coaggregation (Cls for coaggregation, lactose-sensitive) and in the concentrations of particular cell surface antigens (Cap for cell antigen profile) in strains that had undergone phase changes in Spp and/or Bhp. Phase variation in all these phenotypes were transitions between high and low levels of activity and each appeared to occur as an independent event. Significant associations (P << 0.0001 by contingency table analysis) between particular phenotypes such as Bhp and Asp and between Asp, Cls and Cap phenotypes, however, were apparent. The results suggest that S. gordonii cells become predisposed to phase variation and that the resulting independent phenotypic changes may give rise to phenotypically diverse streptococcal populations able to accommodate rapid and transient environmental changes in the mouth.

Streptococcus oralis previously identified as uncommon 'Streptococcus sanguis' in Behçet's disease

The relation between the biochemical and serological properties of 'Streptococcus sanguis' was studied to characterize the strains isolated from dental plaque of patients with Behçet's disease and controls. Seven reference and 100 clinical strains preserved by the Behçet's Disease Research Committee of Japan were identified using established criteria and differentiated with antisera against Strep. oralis ATCC 10557, Strep. sanguis ATCC 10556 and 'Strep. sanguis' ST7, compatible with the criteria. Uncommon serovars (serotypes) KTH-1 (= ATCC 49298), KTH-2 (= ATCC 49296), KTH-3 (= ATCC KTH-4 (= ATCC 49297) and B220 (serovar KTH-1) with both IgA1 protease and neuraminidase (sialidase) were identified as Strep. oralis, whereas common serovars ST3 with IgA1 protease alone and ST7 without both enzymes were identified as Strep. sanguis and Strep. gordonii, respectively. Isolates previously ranked as uncommon serovars were identified as Strep. oralis, whereas the rest ranked as common serovars were identified as the same species as those of the grouping strains. A soft-agar technique was available for species identification except for Strep. oralis serovar KTH-1 reacting with the antiserum against Strep. gordonii ST7. The frequency of isolation of Strep. oralis was higher in Behçet's disease (52%) than in controls (38%), but no difference was observed between the properties of the two groups of isolates. Strep. oralis virulence factors may be involved in breach the mucosal barrier in patients with specific reactivity to these antigens and inducing Behçet's disease.

The influence of morphological variation on Candida albicans adhesion to denture acrylic in vitro

Using denture acrylic pieces coated with either whole human stimulated saliva or oral streptococci, the binding ability of three different Candida albicans strains was investigated. The C. albicans strains include a clinical isolate with the commonly observed, smooth, round colonial morphology (strain 613p), a morphological variant spontaneously derived from the clinical isolate strain 613p (strain 613m1BK) and a clinical isolate from an oral lesion that was also a morphological variant upon primary isolation (strain 228). Levels of adhesion to the acrylic pieces were determined radiometrically using C. albicans cells metabolically labelled with [35S]-methionine. Whole stimulated saliva significantly increased the binding of all strains compared to uncoated acrylic. However, the level of binding of strain 613p to saliva-coated acrylic was significantly greater than the levels observed for the morphological variant strain 613m1BK. Coating acrylic pieces with either Streptococcus sanguis NCTC 10904, Strep. mutans GS-5 or Strep. sobrinus ATCC 27352 instead of saliva resulted in significantly greater binding by strain 613p compared to uncoated acrylic. Pre-coating the acrylic with the oral streptococci did not significantly increase the binding of morphological variant strains 613m1BK and 228 compared to uncoated acrylic. In general, preincubation of adherent streptococci with sucrose to induce the synthesis of extracellular carbohydrate polymers did not significantly increase the binding levels of the C. albicans strains above those observed using streptococci in buffer alone. Compared to its parental strain 613p, morphological variant strain 613m1BK adhered poorly to denture acrylic coated with either salivary constituents or oral streptococci, while strain 228 adhered to the same substrates at an intermediate level. Furthermore, physical disaggregation of clusters of the morphological variant strain 613m1BK did not appear to increase its binding capacity to saliva-coated denture acrylic. The effect of whole stimulated saliva on the adherence of C. albicans 613p to a variety of plastic substrates in addition to denture acrylic was examined. Overall, saliva pre-coating of the various plastics promoted C. albicans 613p adhesion. The adhesion of strain 613p to denture acrylic coated with whole stimulated saliva from each of five different donors or with parotid and submandibular/sublingual saliva from each of two donors was also examined. Regardless of donor, a coating of whole stimulated saliva significantly increased the binding of strain 613p to denture acrylic compared to uncoated acrylic. In addition, a coating of parotid saliva significantly increased the binding of strain 613p to denture acrylic compared to submandibular/sublingual saliva.

Identification of a gene, rgg, which regulates expression of glucosyltransferase and influences the Spp phenotype of Streptococcus gordonii Challis

Streptococcus gordonii Challis was previously shown to give rise to phase variants expressing high (Spp+) or low (Spp-) levels of extracellular glucosyltransferase (GTF) activity. Here, shotgun cloning of an S. gordonii Spp+ chromosomal digest resulted in a chimeric plasmid (pAM5010) able to complement the Spp- phenotype. In addition, introduction of pAM5010 into an Spp+ strain resulted in a 10-fold increase in GTF expression. Deletion analysis of pAM5010 identified a 1.2-kb DNA segment which exhibited the same functional properties as pAM5010. Nucleotide sequence analysis of this region revealed a gene approximately 1 kb in size. The gene was designated rgg. Disruption of the chromosomal rgg gene open reading frame in an Spp+ strain resulted in strain DS512, which displayed an Spp(-)-like phenotype and had 3% of wild-type GTF activity. A plasmid containing the rgg gene was able to complement the DS512 phenotype and significantly increase GTF expression above wild-type levels. Sequence analysis and other data showed that the S. gordonii GTF determinant, designated gtfG, is located 66 bp downstream of the rgg gene. The sequence also revealed interesting inverted repeats which may play a role in the regulation of gtfG. We conclude that rgg positively regulates the expression of GTF and influences expression of the Spp phenotype.

Surface structures (peritrichous fibrils and tufts of fibrils) found on Streptococcus sanguis strains may be related to their ability to coaggregate with other oral genera

We screened 36 strains of Streptococcus sanguis biotype I and 8 strains of S. sanguis biotype II for the presence of surface structures and for their ability to coaggregate with Actinomyces viscosus, Actinomyces naeslundii, and Fusobacterium nucleatum. Negative staining under an electron microscope revealed detectable surface structures on all S. sanguis strains. The majority of strains (38 of 44) carried peritrichous fibrils, which have an irregular profile and no distinct width. They usually appeared as a fringe with a constant width around the cell. Strains selected for measurement had a fringe with an average length of 72.4 +/- 8.5 nm on biotype I strains and 51.6 +/- 3.3 nm on biotype II strains. Some fibrillar biotype I strains carried an additional, longer (158.7 +/- 33.1 nm) type of fibril projecting through the shorter fibrils. Fibrillar density was characteristic for each strain, ranging from very dense on all cells in a population to very sparse on a few cells in a population. A small group of six strains carried tufts of fibrils in a lateral or polar position on the cell. Either one or two lengths of fibril were present in the tuft depending on the strain. One strain carried both peritrichous fibrils and fimbriae. Fimbriae are flexible structures with a constant width (4.5 to 5.0 nm) all along their length but very variable lengths (less than or equal to 0.7 micron) on each cell. S. sanguis I and II both included strains with peritrichous fibrils and tufts of fibrils, but the mixed morphotype strain was confined to biotype II. Fibrils were present on cells at all stages throughout the growth cycle for the strains tested. Freshly isolated fibrillar strains coaggregated consistently well with A. viscosus and A. naeslundii, although some fibrillar reference strains lacked the ability. In addition, all tufted strains could not coaggregate, but the strains with the mixed morphotype coaggregated well. Coaggregation with F. nucleatum was very strong for the fibrillar strains, but less strong for the tufted strains. We discuss the possible correlation between S. sanguis surface structure and ability to coaggregate.

Neuraminidase activity: a biochemical marker to distinguish Streptococcus mitis from Streptococcus sanguis

Selected reference and freshly isolated strains of Streptococcus mitis (mitior) and Streptococcus sanguis were assayed for cell-associated neuraminidase activity by their ability to hydrolyze [3H-] sialyllactitol. A cell-associated neuraminidase was detected with S. mitis and S. sanguis serotype II (reclassified as S. mitis) but not with S. sanguis serotypes I and III. Neuraminidase activity of S. mitis correlated with this organism's inability to hydrolyze arginine, aesculin, and few, if any, sugars. The findings indicate that the presence of cell-associated neuraminidase activity is useful for the taxonomic classification of S. mitis.

Purification and immunochemical characterization of Streptococcus sanguis ATCC 10557 serotype II carbohydrate antigen

Cell wall carbohydrate antigen of Streptococcus sanguis ATCC 10557 (serotype II/biotype B) was extracted from purified cell walls by treatment with 5% trichloroacetic acid at 4 degrees C for 8 h. The extract was purified by chromatography on DEAE-Sephadex A-25 and Sephadex G-100 columns. The purified carbohydrate antigen produced a single precipitin band against anti-type II serum, which fused with the band produced by the autoclaved extract or the phenol-water extract of the S. sanguis cells. The type II antigen was a polysaccharide composed of glucose, galactose, rhamnose, and N-acetylgalactosamine in a molar ratio of approximately 3:6:3:2. Quantitative precipitin inhibition tests with various haptenic sugars indicated that N-acetylgalactosamine was a major determinant of the type II antigen.

Purification and immunochemical characterization of Streptococcus sanguis serotype I carbohydrate antigen

The serotype-specific antigen of Streptococcus sanguis ST3 (serotype I, biotype A) was extracted, chromatographically purified, and characterized by immunological and chemical methods. The antigen was extracted from purified cell walls with hot trichloroacetic acid, followed by ion-exchange chromatography on a DEAE-Sephadex A-25 column and gel filtration through a Sephadex G-100 column. A peak fraction was obtained that gave a single precipitin band when reacted with anti-type I serum. The type I antigen was a polysaccharide composed of glucose, rhamnose, and N-acetylglucosamine in a molar ratio of 1.4:2.5:1.0. Quantitative precipitin inhibition tests with various haptenic sugars indicated that an alpha-glucosidic linkage is the immunodeterminant of the type I antigen.

Colonization and cariogenic potential in hamsters of the bacterium Streptococcus sanguis isolated from human dental plaque

Strains of Strep. sanguis, freshly isolated from human dental plaque, were successfully implanted into albino hamsters. Transmission of the organisms from infected to uninfected animals occurred naturally. The transfer was as effective between unrelated hamsters as between dams and their offspring. Three of the strains tested did not cause caries in hamsters. Laboratory strains of Strep. sanguis did not colonize the hamsters. Two morphological variants of Strep. sanguis with different abilities to adhere to whale dentine in vitro, could infect hamsters; the more adhering phenotype was detected earlier and more frequently.

Adherence of Streptococcus sanguis clinical isolates to smooth surfaces and interactions of the isolates with Streptococcus mutans glucosyltransferase

Streptococcus sanguis isolated from human dental plaque were grown in Todd-Hewitt broth. Cells were collected by centrifugation and lyophilized after extensive washing with water. The cell-associated glucosyltransferase (GTase) activities of S. sanguis strains were assayed with [14C]sucrose. Strain differences in GTase activity were significant within the same serotype or biotype or both. The ability of S. sanguis cells to adhere to smooth glass surfaces was generally weak, irrespective of significant cell-associated GTase activity synthesizing water-insoluble, gel-like glucans. Resting cells of most S. sanguis strains bound extracellular GTase from Streptococcus mutans strain B13 (serotype d), resulting in the strong adherence of the S. sanguis cells to smooth glass surfaces in the presence of sucrose. Conversely, S. mutans B13 cells also could bind extracellular GTase from some strains of S. sanguis examined. The sucrose-dependent adherence of S. mutans cells was not altered, although S. sanguis strains from which the extracellular GTases were obtained did not produce significant adherence in the presence of sucrose. In view of these findings, it was suggested that S. mutans GTase could affect the adherence of S. sanguis to smooth tooth surfaces in the oral cavity.