Stability and resilience of oral microcosms toward acidification and Candida outgrowth by arginine supplementation.

Dysbiosis induced by low pH in the oral ecosystem can lead to caries, a prevalent bacterial disease in humans. The amino acid arginine is one of the pH-elevating agents in the oral cavity. To obtain insights into the effect of arginine on oral microbial ecology, a multi-plaque "artificial mouth" (MAM) biofilm model was inoculated with saliva from a healthy volunteer and microcosms were grown for 4 weeks with 1.6 % (w/v) arginine supplement (Arginine) or without (Control), samples were taken at several time-points. A cariogenic environment was mimicked by sucrose pulsing. The bacterial composition was determined by 16S rRNA gene amplicon sequencing, the presence and amount of Candida and arginine deiminase system genes arcA and sagP by qPCR. Additionally, ammonium and short-chain fatty acid concentrations were determined. The Arginine microcosms were dominated by Streptococcus, Veillonella, and Neisseria and remained stable in time, while the composition of the Control microcosms diverged significantly in time, partially due to the presence of Megasphaera. The percentage of Candida increased 100-fold in the Control microcosms compared to the Arginine microcosms. The pH-raising effect of arginine was confirmed by the pH and ammonium results. The abundances of sagP and arcA were highest in the Arginine microcosms, while the concentration of butyrate was higher in the Control microcosms. We demonstrate that supplementation with arginine serves a health-promoting function; it enhances microcosm resilience toward acidification and suppresses outgrowth of the opportunistic pathogen Candida. Arginine facilitates stability of oral microbial communities and prevents them from becoming cariogenic.

Xylitol: effects on the acquisition of cariogenic species in infants.

PURPOSE: The purpose of this study was to examine the effects of xylitol gum (XG) on the acquisition pattern of 39 bacterial species, including mutans streptococci (MS), in infants. METHODS: Ninety-seven mothers (MS counts > 10(5) CFU/ml) were randomly divided into 4 groups and received: (1) XG (4.2 gm/day); (2) XG (6 months after baseline exams); (3) sorbitol gum (4.2 gm/day); or (4) no gum. Groups 1 and 3 chewed gum 3 times a day for 9 months. Microbiota of plaque and saliva samples from the mother-child pairs were analyzed by culturing and via checkerboard DNA-DNA hybridization. RESULTS: MS was isolated from 33% of the predentate infant (< or =5 months old) baseline saliva samples and from 41% of the saliva and 65% of the plaque samples at the final visit. At baseline, positive responses to "mother's checking of baby's food temperature using baby's spoon" and "starting a bottle after stopping breast-feeding" were significant predictors (P = .009 and P < .001, respectively) of infant's total streptococci counts. At the final visit (9 months later), there were no significant differences between treatment groups for infants' 39 microbial plaque species, including MS. CONCLUSIONS: Maternal use of xylitol gum did not result in statistically significant differences in the microbial plaque composition of 9- to 14-month-old infants.

Variation in bacterial DGGE patterns from human saliva: over time, between individuals and in corresponding dental plaque microcosms.

OBJECTIVE: Eubacterial 16S rDNA fingerprints of human saliva and dental plaque microcosm biofilms grown in the multi-plaque artificial mouth (MAM) were characterised using denaturing gradient gel electrophoresis (DGGE). DESIGN: The stability of the bacterial community in the saliva of one individual collected over 7 years was assessed and compared with bacterial patterns in the saliva of 10 different individuals. DGGE was also used to assess changes in bacterial composition between saliva and mature plaque microcosms developed in the MAM from these 10 individual saliva samples. RESULTS: A relatively stable bacterial community (>87% concordance) was maintained within the individual oral environment of the standard donor over 7 years of monitoring. By comparison, DGGE fingerprint patterns of saliva from 10 different donors displayed greater variability (66% concordance). Variability between individual DGGE profiles increased further in mature plaque microcosms grown from the saliva of the 10 donors (52% concordance) with an increase in detected species diversity and evidence for conserved similarity and hence the maintenance of organisation during community development. CONCLUSIONS: These results suggest that stable ecological conditions were maintained long-term within the oral environment of the individual saliva donor but that transient fluctuations also occurred. The ecology and predominating microbiota in different individuals was host-specific and these differences were maintained to a degree during development into mature plaque microcosms. These findings also demonstrate the potential usefulness of applying DGGE to monitor temporal and developmental changes and possibly pathogenic patterns in oral bacterial communities from saliva and plaque.

Application of carbon source utilization patterns to measure the metabolic similarity of complex dental plaque biofilm microcosms.

Biolog technology was applied to measure the metabolic similarity of plaque biofilm microcosms, which model the complex properties of dental plaque in vivo. The choice of Biolog plate, incubation time, and incubation conditions strongly influenced utilization profiles. For plaque biofilm microcosms, Biolog GP2 plates incubated anaerobically in an H2-free atmosphere gave the clearest profile. To test the application of the Biolog GP2 assay, plaque microcosms were developed under different nutrient conditions in which the frequency of sucrose application was varied. Cluster analysis of Biolog GP2 data from 10 microcosm biofilms correlated with sucrose frequency. Aciduric bacteria (Streptococcus mutans plus lactobacilli) predominated in the plaques receiving high-frequency sucrose applications. Agreement between the Biolog GP2 groupings with nutrient and compositional changes suggests that Biolog analysis is a valuable technique for analyzing the metabolic similarity of dental plaque biofilm microcosms and other high-nutrient or predominantly anaerobic ecosystems.