Retention of antimicrobial activity in plaque and saliva following mouthrinse use in vivo.

The aim of this study was to determine the contribution of plaque and saliva towards the prolonged activity, also called substantivity, of three antimicrobial mouthrinses (Listerine®, Meridol®, Crest Pro Health®), used in combination with a toothpaste (Prodent Coolmint®). Volunteers brushed for 4 weeks with a toothpaste without antimicrobial claims, while during the last 2 weeks half of the volunteers used an antimicrobial mouthrinse in addition to brushing. At the end of the experimental period, plaque and saliva samples were collected 6 h after oral hygiene, and bacterial concentrations and viabilities were determined. The contribution of plaque and saliva towards substantivity was assessed by combining plaque obtained after mechanical cleaning only with plaque and saliva obtained after additional use of an antimicrobial rinse. Subsequently, resulting viabilities of the combined plaques were determined. The viabilities of plaque samples after additional rinsing with mouthrinses were lower than of plaque obtained after mechanical cleaning only, regardless of the rinse involved. Moreover, plaque collected 6 h after rinsing with antimicrobial mouthrinses contained a surplus of antimicrobial activity. Only Listerine showed decreased viability in saliva, but none of the mouthrinses showed any residual antimicrobial activity in saliva. The findings indicate that plaque left behind after mechanical cleaning contributes to the prolonged substantivity of antimicrobial mouthrinses.

Reduction of periodontal pathogens adhesion by antagonistic strains.

INTRODUCTION: Periodontitis results from a shift in the subgingival microflora into a more pathogenic direction with Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans considered as periodontopathogens. In many cases, treatment procures only a temporary shift towards a less pathogenic microflora. An alternative treatment could be the deliberate colonization of pockets with antagonistic microorganisms to control the adhesion of periodontopathogens. The aim of this study was to identify bacterial strains that reduce adhesion of periodontopathogens to surfaces. METHODS: Streptococcus sanguinis, Streptococcus crista, Streptococcus salivarius, Streptococcus mitis, Actinomyces naeslundii, and Haemophilus parainfluenzae were evaluated as potential antagonists against P. gingivalis ATCC 33277, P. intermedia ATCC 49046, and A. actinomycetemcomitans ATCC 43718 as periodontopathogens. Adhesion of periodontopathogens to the bottom plate of a parallel plate flow chamber was studied in the absence (control) and the presence of pre-adhering antagonistic strains up to a surface coverage of 5%. RESULTS: The largest reduction caused by antagonistic strains was observed for P. gingivalis. All antagonistic strains except S. crista ATCC 49999 inhibited the adhesion of P. gingivalis by at least 1.6 cells per adhering antagonist, with the largest significant reduction observed for A. naeslundii ATCC 51655 (3.8 cells per adhering antagonist). Adhering antagonists had a minimal effect on the adhesion of A. actinomycetemcomitans ATCC 43718. Intermediate but significant reductions were perceived for P. intermedia, most notably caused by S. mitis BMS. CONCLUSION: The adhesion of P. gingivalis was inhibited best by antagonistic strains, while S. mitis BMS appeared to be the most successful antagonist.

Influence of biosurfactant on interactive forces between mutans Streptococci and enamel measured by atomic force microscopy.

Although interactive forces, influenced by environmental conditions, between oral bacteria and tooth surfaces are important for the development of plaque, they have never been estimated. It is hypothesized that interactive forces, as measured by atomic force microscopy, between enamel with or without a pellicle and two strains of mutans streptococci become less attractive by the application of a Streptococcus mitis BMS biosurfactant coating. Upon approach of each of the strains toward bare and pellicle-coated enamel, adsorbed biosurfactant increased the range of the repulsive forces. Upon retraction of the enamel surface, small adhesion forces (0.8-0.9 nN) were measured for bare enamel that almost disappeared after biosurfactant coating. The prevalence and magnitude of the adhesion forces also decreased upon pellicle-coating of the enamel, with a minor effect of adsorbed biosurfactant. These findings indicate that adsorbed S. mitis BMS biosurfactant changes the interactive forces between the mutans streptococci studied and enamel, explaining the effects of biosurfactant on adhesion.

Inhibition of Streptococcus mutans NS adhesion to glass with and without a salivary conditioning film by biosurfactant- releasing Streptococcus mitis strains.

The release of biosurfactants by adhering microorganisms as a defense mechanism against other colonizing strains on the same substratum surface has been described previously for probiotic bacteria in the urogenital tract, the intestines, and the oropharynx but not for microorganisms in the oral cavity. Two Streptococcus mitis strains (BA and BMS) released maximal amounts of biosurfactants when they were grown in the presence of sucrose and were harvested in the early stationary phase. The S. mitis biosurfactants reduced the surface tensions of aqueous solutions to about 30 to 40 mJ m(-2). Biochemical and physicochemical analyses revealed that the biosurfactants released were glycolipids. An acid-precipitated fraction was extremely surfactive and was identified as a rhamnolipidlike compound. In a parallel-plate flow chamber, the number of Streptococcus mutans NS cells adhering to glass with and without a salivary conditioning film in the presence of biosurfactant-releasing S. mitis BA and BMS (surface coverage, 1 to 4%) was significantly reduced compared with the number of S. mutans NS cells adhering to glass in the absence of S. mitis. S. mutans NS adhesion in the presence of non-biosurfactant-releasing S. mitis BA and BMS was not reduced at all. In addition, preadsorption of isolated S. mitis biosurfactants to glass drastically reduced the adhesion of S. mutans NS cells and the strength of their bonds to glass, as shown by the increased percentage of S. mutans NS cells detached by the passage of air bubbles through the flow chamber. Preadsorption of the acid-precipitated fraction inhibited S. mutans adhesion up to 80% in a dose-responsive manner. These observations indicate that S. mitis plays a protective role in the oral cavity and protects against colonization of saliva-coated surfaces by cariogenic S. mutans.

Streptococcus thermophilus and its biosurfactants inhibit adhesion by Candida spp. on silicone rubber.

The adhesion of yeasts, two Candida albicans and two Candida tropicalis strains isolated from naturally colonized voice prostheses, to silicone rubber with and without a salivary conditioning film in the absence and presence of adhering Streptococcus thermophilus B, a biosurfactant-releasing dairy isolate, was studied. Coverage of 1 to 4% of the surface of silicone rubber substrata with adhering S. thermophilus B gave significant reductions in the initial yeast adhesion regardless of the presence of a conditioning film. Mechanistically, this interference in yeast adhesion by S. thermophilus B was not due to direct physical effects but to biosurfactant release by the adhering bacteria, because experiments with S. thermophilus B cells that had released their biosurfactants prior to adhesion to silicone rubber and competition with yeasts did not show interference with initial yeast adhesion. The amounts of biosurfactants released were highest for mid-exponential- and early-stationary-phase bacteria (37 mg.g of cells-1 [dry weight]), but biosurfactants released by stationary-phase bacteria (14 mg.g of cells-1 [dry weight]) were the most surface active. The crude biosurfactants released were mixtures of various components, with a glycolipid-like component being the most surface active. A lipid-enriched biosurfactant fraction reduced the surface tension of an aqueous solution to about 35 mJ.m-2 at a concentration of only 0.5 mg.ml-1. The amount of biosurfactant released per S. thermophilus B cell was estimated to be sufficient to cover approximately 12 times the area of the cross section of the bacterium, making biosurfactant release a powerful defense weapon in the postadhesion competition of the bacterium with microorganisms such as yeasts. Preadsorption of biosurfactants to the silicone rubber prior to allowing yeasts to adhere was as effective against C. albicans GB 1/2 adhesion as covering 1 to 2% of the silicone rubber surface with adhering S. thermophilus B, but a preadsorbed biosurfactant layer was less effective against C. tropicalis GB 9/9.