Effect of Lactobacillus rhamnosus strain GG (ATCC 53103) on the growth of Streptococcus sobrinus in vitro.

Lactobacillus GG, a recently characterized L. rhamnosus GG strain (ATCC 53103), has been shown to exert inhibitory activity against a variety of bacterial species, including streptococci. We isolated and studied the effect of the inhibitory substance of Lactobacillus GG on some oral streptococci. The inhibitory activity of the isolated substance was weak, but some growth inhibition was observed in Streptococcus sobrinus pretreated with the substance in comparison with untreated controls. Zones of growth inhibition on agar plates were apparent only at pH values below 5, indicating that the inhibitory activity was restricted to a low pH range. Growth curve experiments showed a statistically significant inhibition between series with and without the isolated substance (P < 0.05). The ultrastructure of S. sobrinus was not affected when treated with the inhibitory substance. The Lactobacillus GG itself did not ferment sucrose. The results offer interesting perspectives for future research focusing on the protective function of normal flora and in the attempt to replace harmful bacterial species in oral microflora with less harmful ones.

Effect of polyclonal and monoclonal antibodies on surface properties of Streptococcus sobrinus.

In this study, the effect of antibody adsorption on physicochemical properties of Streptococcus sobrinus was studied. Bacteria were preincubated with polyclonal antibodies or with OMVU10, a monoclonal antibody (MAb) reactive with S. sobrinus. The zeta potentials and the hydrophobicity as determined by microbial adhesion to hydrocarbons were measured in potassium phosphate buffer with a pH ranging from 2 to 9. S. sobrinus preincubated with polyclonal antibodies was positively charged at pH 2, 3, and 4 and had an isoelectric point at pH 4.8. Untreated S. sobrinus cells or cells preincubated with MAbs were negatively charged over the whole pH range. X-ray photoelectron spectroscopy showed a decrease in O/C and P/C ratios for bacteria preincubated with polyclonal antibodies. A combination of the pH-dependent zeta potential and the X-ray photoelectron spectroscopy data of the overall chemical composition of the cell surface suggests that polyclonal antibody adsorption occurs through blocking of surface phosphate. The measurement of hydrophobicity by microbial adhesion to hydrocarbons revealed that S. sobrinus preincubated with polyclonal antibodies was hydrophobic (90% of the bacteria bound to hexadecane), whereas the controls were relatively hydrophilic. S. sobrinus preincubated with OMVU10 was found to be more hydrophobic than the controls at pH 5 and 7. Hydrophobicity as measured by water contact angles showed an increase in hydrophobicity when S. sobrinus was preincubated with polyclonal antibodies. The epitopes to which the antibodies are directed were visualized by immunogold labeling and electron microscopy. The results suggested that OMVU10 is reactive with only a few epitopes of the cell surface, whereas polyclonal antibodies were found to be reactive with many epitopes. In conclusion, adsorption of polyclonal antibodies was found to influence the overall physicochemical surface properties of the organism, probably by forming a coating over the whole cell surface. Adsorption of MAbs was more localized, which could explain their lesser influence on these surface properties.

[Prevention of cariogenic dental plaque. Study of the structures implicated in the adhesion and coaggregation in Streptococcus mutans and Streptococcus sobrinus]. / Prévention de la plaque dentaire cariogène étude des structures impliquées dans l'adhésion et la coagrégation chez Streptococcus mutans et Streptococcus sobrinus.

Cariogenic dental plaque may be assimilated to a biofilm resulting from the adhesion of S. mutans, then from the coaggregation of other streptococci, or other genus. We used a static monospecific biofilm model. Supports or bacteria were treated with inhibitors before adhesion in order to clarify the nature of adhesins responsible for the primary adhesion of S. mutans and S. sobrinus on Tygon. To determine the bindings of coaggregation, inhibitors were applied on one-day-old biofilms. Analysis of effects were performed by automatic inoculator Spiral (Interscience) for microbiological methods, and by SEM JEOL 5400 LV for microscopic methods. In the aim of preventing adhesion and coaggregation, different traps were assayed:sugars, chemical inhibitors such as F- and EDTA salts. Of these, only the latter showed efficiency. This confirmed the role of bivalent mineral ions and electrostatic attraction forces in the adhesion and coaggregation of streptococci.

Comparison of cell sediment and surface grown "test plaque" using scanning electron microscopy.

Scanning electron microscopy was used to compare the morphology, integrity and distribution of bacterial cells in a test plaque grown on the surface of enamel with that of the cell sediment plaque routinely used in a short-term intraoral caries model. Cultures of S. mutans IB-1600 or S. sobrinus 6715-13 were grown in complex media supplemented with either 2.0% sucrose (glucan plaque) or 0.2% glucose (non-glucan plaque). Cell sediment (CS) plaque was prepared by centrifuging the cultures after incubation, recovering the cell sediment, and spreading it on Metricel membrane filter paper. Surface grown (SG) plaque was prepared by suspending saliva-coated bovine enamel in the culture medium, incubating, and recovering the enamel assembly with bacterial accumulations. Cell morphology and integrity, as well as the appearance of glucan-like material produced by the cells, was similar in both CS and SG test plaques. The cell distribution however, varied in the SG plaque from extremes of all cells to all glucan, whereas the cell sediment plaque was more uniform in cell distribution. A highly standardized test plaque minimizes variability in the intraoral caries model. These findings support the contention that the bacterial cells in a cell sediment plaque are similar in morphology, integrity and glucan production to surface grown plaque, and have the added advantage of uniform distribution, which makes the cell sediment plaque more appropriate for intraoral caries model studies.

Localization on the cell surface of streptococcal protein antigen A.

The cellular localization of the major surface protein SpaA of Streptococcus sobrinus 6715 was examined by immunoelectron microscopy with rabbit polyclonal antibodies directed against purified SpaA protein. Immunoelectron microscopic analysis of thin sections of S. sobrinus cells revealed that the SpaA protein is associated with the fibrillar fuzzy coat of S. sobrinus cells and appears to be distributed over the entire surface of S. sobrinus cells.