Effects of Lactobacillus rhamnosus GG on saliva-derived microcosms.

OBJECTIVE: The probiotic strain Lactobacillus rhamnosus GG (LGG) is shown to hamper the presence of mutans streptococci in saliva and may have positive effects on oral health. We investigated the effects of LGG on the cariogenic potential and microbial composition of saliva-derived microcosms. DESIGN: Single and dual species biofilms of LGG and Streptococcus mutans, and saliva-derived microcosms with or without LGG were grown in an Active Attachment Biofilm model. The microcosms were grown on bovine dentin/enamel discs in the presence or absence of sucrose (suc+/suc-). The presence of LGG was determined by multiplex ligation-dependent probe amplification (MLPA) and real-time PCR. Mutans streptococci (MS) and total viable counts, pH of the spent medium, capacity of lactate formation and integrated mineral loss in dentin was assessed. MLPA was used for identification and relative quantification of 20 oral microorganisms in the microcosms. Principal Component Analysis was applied to MLPA data. RESULTS: LGG inhibited the growth of S. mutans in dual species biofilms and did not affect the pH. LGG established in saliva-derived microcosms and reduced MS counts significantly, but did not affect pH or dentin demineralization. Simultaneous growth of the microcosms with LGG under heavy cariogenic conditions (suc+) introduced a compositional shift in the microbial community. The CFU, real-time PCR and MLPA data correlated significantly. CONCLUSION: We conclude that LGG established into and inhibited the growth of MS in complex saliva-derived biofilms, but this had no significant effect on cariogenic potential of the microcosms. This suggests that other microorganisms besides MS were responsible for increased cariogenicity of sucrose-exposed biofilms.

Effects of probiotic Lactobacillus salivarius W24 on the compositional stability of oral microbial communities.

Probiotics are microorganisms beneficial to gastrointestinal health. Although some strains are also known to possess positive effects on oral health, the effects of most intestinal probiotics on the oral microflora remain unknown. We assessed the ability of the intestinal probiotic Lactobacillus salivarius W24 to incorporate into and to affect the compositional stability and cariogenicity of oral microbial communities. Microtiter plates with hydroxyapatite discs were incubated with W24 ("+W24") or without W24 ("-W24") and saliva from four individuals in plain ("-sucrose") or sucrose-supplemented ("+sucrose") medium. Biofilms were subjected to community profiling by 16S rRNA gene-based Denaturing Gradient Gel Electrophoresis (DGGE) after 72h growth. Diversity (Shannon-Weaver index) and similarities (Pearson correlation) between biofilm communities were calculated. Microcosms "+sucrose" were less diverse and more acidic than "-sucrose" microcosms (p<0.001). The effects of W24 on the community profiles were pH dependent: at pH 4 ("+sucrose"), the respective "+W24" and "-W24" microcosms differed significantly more from each other than if the pH was approximately 7 ("-sucrose"). The pH of "+W24/+sucrose" microcosms was lower (p<0.05) than the pH of the microcosms supplemented with sucrose alone ("-W24/+sucrose"). Although not able to form a monospecies biofilm, L. salivarius W24 established itself into the oral community if inoculated simultaneously with the microcosm. In the presence of sucrose and low pH, W24 further lowered the pH and changed the community profiles of these microcosms. Screening of probiotics for their effects on oral microbial communities allows selecting strains without a potential for oral health hazards.