The cariogenic effect of starch on oral microcosm grown within the dual constant depth film fermenter

Evidence on the link between starch intake and caries incidence is conflicting, therefore the cariogenicity of starch compared with sucrose was explored using a dual Constant Depth Film Fermenter (dCDFF) biotic model system. Bovine enamel discs were used as a substrate and the dCDFF was inoculated using human saliva. CDFF units were supplemented with artificial saliva growth media at a constant rate to mimic resting salivary flow rate over 14 days. The CDFF units were exposed to different conditions, 2% sucrose or 2% starch 8 times daily and either no additional fluoride or 1450 ppm F- twice daily. Bovine enamel discs were removed at intervals (days 3, 7, 10 and 14) for bacterial enumeration and enamel analysis using Quantitative Light Induced Fluorescence (QLF) and Transverse Microradiography (TMR). Results showed that in the absence of fluoride there was generally no difference in mineral loss between enamel exposed to either sucrose or starch when analysed using TMR and QLF (P > 0.05). In the presence of fluoride by day 14 there was significantly more mineral loss under starch than sucrose when analysed with TMR (P < 0.05). It was confirmed that starch and sucrose are similarly cariogenic within the dCDFF in the absence of fluoride. With the aid of salivary amylase, the bacteria utilise starch to produce an acidic environment similar to that of bacteria exposed to sucrose only. In the presence of fluoride, starch was more cariogenic which may be due to the bacteria producing a more hydrophobic intercellular matrix lowering the penetration of fluoride through the biofilm. This is significant as it indicates that the focus on sugars being the primary cause of caries may need re-evaluating and an increase in focus on carbohydrates is needed as they may be similarly cariogenic as sugars if not more so.

Dysbiosis of oral microbiota and its association with salivary immunological biomarkers in autoimmune liver disease

The gut microbiota has recently been recognized to play a role in the pathogenesis of autoimmune liver disease (AILD), mainly primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH). This study aimed to analyze and compare the composition of the oral microbiota of 56 patients with AILD and 15 healthy controls (HCs) and to evaluate its association with salivary immunological biomarkers and gut microbiota. The subjects included 39 patients with PBC and 17 patients with AIH diagnosed at our hospital. The control population comprised 15 matched HCs. Salivary and fecal samples were collected for analysis of the microbiome by terminal restriction fragment length polymorphism of 16S rDNA. Correlations between immunological biomarkers measured by Bio-Plex assay (Bio-Rad) and the oral microbiomes of patients with PBC and AIH were assessed. Patients with AIH showed a significant increase in Veillonella with a concurrent decrease in Streptococcus in the oral microbiota compared with the HCs. Patients with PBC showed significant increases in Eubacterium and Veillonella and a significant decrease in Fusobacterium in the oral microbiota compared with the HCs. Immunological biomarker analysis showed elevated levels of inflammatory cytokines (IL-1β, IFN-γ, TNF-α, IL-8) and immunoglobulin A in the saliva of patients with AILD. The relative abundance of Veillonella was positively correlated with the levels of IL-1β, IL-8 and immunoglobulin A in saliva and the relative abundance of Lactobacillales in feces. Dysbiosis of the oral microbiota is associated with inflammatory responses and reflects changes in the gut microbiota of patients with AILD. Dysbiosis may play an important role in the pathogenesis of AILD.

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.

The influence of oral Veillonella species on biofilms formed by Streptococcus species

Oral Veillonella, Veillonella atypica, Veillonella denticariosi, Veillonella dispar, Veillonella parvula, Veillonella rogosae, and Veillonella tobetsuensis are known as early colonizers in oral biofilm formation. To investigate the role of oral Veillonella, biofilms formed by the co-culture of Streptococcus gordonii, Streptococcus mutans, Streptococcus salivarius, or Streptococcus sanguinis, with oral Veillonella were examined at the species level. The amount of biofilm formed by S. mutans, S. gordonii, and S. salivarius in the presence of the six Veillonella species was greater than that formed in the control experiments, with the exception of S. mutans with V. dispar. In contrast, in the case of biofilm formation by S. sanguinis, the presence of Veillonella species reduced the amount of the biofilm, with the exception of V. parvula and V. dispar. The time-dependent changes in the amount of biofilm and the number of planktonic cells were grouped into four patterns over the 24 combinations. Only that of S. gordonii with V. tobetsuensis showed a unique pattern. These results indicate that the mode of action of this combination differed from that of the other combinations with respect to biofilm formation. It is possible that there may be several factors involved in the interaction between Streptococcus and Veillonella species.

The in vivo dynamics of Streptococcus spp., Actinomyces naeslundii, Fusobacterium nucleatum and Veillonella spp. in dental plaque biofilm as analysed by five-colour multiplex fluorescence in situ hybridization

The formation and composition of dental plaque biofilm in vivo are important factors which influence the development of gingivitis, caries and periodontitis. Studying dental plaque biofilm in in vitro models can cause an oversimplification of the real conditions in the oral cavity. In this study, bovine enamel slabs were fixed in an individual acrylic appliance in situ to quantify dental plaque formation and composition using multiplex fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy. Each of the five oligonucleotide probes used for FISH was specific for either eubacteria or one of four frequently isolated bacterial constituents belonging to early and late colonizers of tooth surfaces. The thickness of formed biofilm increased from 14.9+/-5.0 microm after 1 day to 49.3+/-11.6 microm after 7 days. Streptococcus spp. were predominant in 1-day-old dental plaque and decreased significantly after 7 days (P=0.0061). Compared to the first day, Fusobacterium nucleatum decreased after 2 days and increased significantly after 7 days (P=0.0006). The decreases of Actinomyces naeslundii content on day 2 and day 7 were significant (P=0.0028). Changes in Veillonella spp. were not significant during the study period (P >0.05). The results showed that an in vivo observation period of 7 days was required to detect significant changes in Streptococcus spp. and F. nucleatum. The multiplex FISH used is suitable for analysing the dynamics of four important bacterial constituents in the oral biofilm in epidemiological studies.

Microstructural differences between single-species and dual-species biofilms of Streptococcus mutans and Veillonella parvula, before and after exposure to chlorhexidine

Dual-species biofilms of Streptococcus mutans and Veillonella parvula are less susceptible to antimicrobials than single-species biofilms of the same microorganisms. The microstructure of single and dual-species biofilms of S. mutans and/or V. parvula was visualized to find out whether the spatial arrangement of bacteria in biofilms is related to survival strategies against antimicrobials. Biofilms were grown in glass-bottomed 96-well microtiter plates and exposed to chlorhexidine at 48 h. Fluorescent probes were used for staining. The microstructure of biofilms was analyzed by confocal scanning laser microscopy at 48, 96, 192, and 264 h. Spatial arrangement analysis was performed using DAIME software for 48 h biofilms. A decrease in the viability and thickness in all types of biofilms was detected after chlorhexidine treatment in time. In untreated biofilms, clustering was observed. In chlorhexidine-treated single-species biofilms, bacteria were dispersed. However, the most prominent clustering was observed in chlorhexidine-treated dual-species biofilm bacteria, which had a higher survival rate compared with chlorhexidine-treated single-species biofilms. Bacteria in dual-species biofilms establish a specific spatial arrangement, forming clusters within distances below 1.2 microm as a survival strategy against antimicrobials while the same bacteria lack this defensive construction in a single-species biofilm.

Rapid succession within the Veillonella population of a developing human oral biofilm in situ

Streptococci are the primary component of the multispecies oral biofilm known as supragingival dental plaque; they grow by fermentation of sugars to organic acids, e.g., lactic acid. Veillonellae, a ubiquitous component of early plaque, are unable to use sugars; they ferment organic acids, such as lactate, to a mixture of shorter-chain-length acids, CO(2), and hydrogen. Certain veillonellae bind to (coaggregate with) streptococci in vitro. We show that, between 4 and 8 hours into plaque development, the dominant strains of Veillonella change in their phenotypic characteristics (coaggregation and antibody reactivity) as well as in their genotypic characteristics (16S RNA gene sequences as well as strain level fingerprint patterns). This succession is coordinated with the development of mixed-species bacterial colonies. Changes in community structure can occur very rapidly in natural biofilm development, and we suggest that this process may influence evolution within this ecosystem.

Differences between single- and dual-species biofilms of Streptococcus mutans and Veillonella parvula in growth, acidogenicity and susceptibility to chlorhexidine

Streptococcus mutans, considered a primary pathogen in dental caries, thrives in dental plaque, which is a multispecies biofilm. Metabolic interactions between S. mutans and Veillonella parvula have been suggested. In this study we developed a biofilm model to quantify single-species (S. mutans or V. parvula) and dual-species (S. mutans and V. parvula) biofilm formation, and we identified the differences between the respective biofilms in terms of growth, acid formation, and response to chlorhexidine. Polystyrene 96-well microtiter plates were used for biofilm formation. These biofilms were exposed to various chlorhexidine concentrations (0.025-0.4 mg ml(-1)) and treatment conditions. Growth of the biofilms and the effects of chlorhexidine were evaluated by viable counts. Viability of the two species in all biofilm types was similar ( approximately 10(8) colony-forming units per well) after 72 h. Lactic acid accumulation of dual-species biofilms was significantly lower at 48 and 72 h than single-species biofilms of S. mutans. Dual-species biofilms were less susceptible to chlorhexidine than single-species biofilms when a neutralization step was included. These results indicate that bacteria in dual-species biofilms have different properties from bacteria in single-species biofilms.

[Recovery of Veillonella from saliva]

Veillonella spp. are anaerobic gram-negative cocci associated to oral health. Different types of cultures have been reported for the isolation of these microorganisms. Veillonella spp. colonies produce a red fluorescence, which is made visible through ultraviolet light and disappears in contact with oxygen. This feature would be very useful for rapid presumptive identification. The aims of this study were: 1. to compare the Rogosa selective medium for Veillonella with the cultures recommended by different authors in order to determine best saliva recovery, since this sample is generally used to determine the presence and predominance of this bacteria; 2. to detect red fluorescence production on these different culture media as a rapid method for identification. Selective medium for Veillonella, Schaedler agar for anaerobic bacteria with vitamin K, thioglycollate agar, brain heart infusion agar, Brucella agar, trypticase soy agar, and Columbia agar, all of them with and without the addition of vancomycin, and laked blood were used for this study. The tested sample was a saliva pool. Both, Veillonella colonies, and the total number of microorganisms were counted, and expressed as CFU/ml of saliva. The greatest Veillonella recovery in saliva was obtained with the selective medium for Veillonella with vancomycin and laked blood. The production of fluorescence was only observed in this medium.

Interspecies communication in Streptococcus gordonii-Veillonella atypica biofilms: signaling in flow conditions requires juxtaposition

During the development of human oral biofilm communities, the spatial arrangement of the bacteria is thought to be driven by metabolic interactions between them. Streptococcus gordonii and Veillonella atypica, two early colonizing members of the dental plaque biofilm, have been postulated to participate in metabolic communication; S. gordonii ferments carbohydrates to form lactic acid, which is a preferred fermentation substrate for V. atypica. We found that, during agar-plate coculture of these organisms, a signaling event occurs that results in increased expression of the S. gordonii alpha-amylase-encoding gene amyB. Confocal scanning laser microscopy of coculture flowcell-grown biofilms using human saliva as the sole nutrient showed that V. atypica caused S. gordonii to increase expression of a PamyB-'gfp transcriptional fusion in a spatially resolved fashion. In this open system, only those streptococci in mixed-species microcolonies containing V. atypica expressed GFP; nearby S. gordonii colonies that lacked V. atypica did not express GFP. In a closed system containing S. gordonii and V. atypica, flow cytometric analysis showed that S. gordonii containing the PamyB-'gfp reporter plasmid exhibited mean fluorescence levels 20-fold higher than did S. gordonii that had not been incubated with V. atypica. Thus, in a closed system where a diffusible signal can accumulate above a required threshold, interspecies signaling mediates a change in gene expression. We provide evidence that, in open systems like those that predominate in natural biofilms, diffusible signals between species are designed to function over short distances, on the order of 1 mum.

An in vitro study into the corrosion of intra-oral magnets in the presence of dental amalgam

The aim of this investigation was to study the corrosion behaviour and products of uncoated neodymium-iron-boron magnets in the presence of dental amalgam. Microcosm plaques were grown on discs of neodymium-iron-boron magnets or amalgam in a constant depth film fermentor. The biofilms were supplied with artificial saliva and growth was determined by viable counting. The results showed that the neodymium-iron-boron magnets corroded with an average daily weight loss of 0.115 +/- 0.032 per cent. However, when the magnets were in close proximity to the amalgam the amount of corrosion was reduced to a daily loss of 0.066 +/- 0.023 per cent. The highest loss of constituent elements from the corrosion products of the magnets was observed for iron. The composition of the microcosm plaques altered markedly between the two materials with less streptococci and more Veillonella spp. present in the biofilms grown on magnets in the presence of amalgam. The corrosion of neodymium-iron-boron magnets is limited and in the presence of amalgam is reduced further. This suggests that amalgam present in the mouth will not cause an increased clinical risk in terms of biocompatibility with neodymium-iron-boron magnets.

Mass transport of macromolecules within an in vitro model of supragingival plaque

The aim of this study was to examine the diffusion of macromolecules through an in vitro biofilm model of supragingival plaque. Polyspecies biofilms containing Actinomyces naeslundii, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus sobrinus, Veillonella dispar, and Candida albicans were formed on sintered hydroxyapatite disks and then incubated at room temperature for defined periods with fluorescent markers with molecular weights ranging from 3,000 to 900,000. Subsequent examination by confocal laser scanning microscopy revealed that the mean square penetration depths for all tested macromolecules except immunoglobulin M increased linearly with time, diffusion coefficients being linearly proportional to the cube roots of the molecular weights of the probes (range, 10,000 to 240,000). Compared to diffusion in bulk water, diffusion in the biofilms was markedly slower. The rate of diffusion for each probe appeared to be constant and not a function of biofilm depth. Analysis of diffusion phenomena through the biofilms suggested tortuosity as the most probable explanation for retarded diffusion. Selective binding of probes to receptors present in the biofilms could not explain the observed extent of retardation of diffusion. These results are relevant to oral health, as selective attenuated diffusion of fermentable carbohydrates and acids produced within dental plaque is thought to be essential for the development of carious lesions.

Selection of dairy bacterial strains as probiotics for oral health

The aim of the present study was to select bacterial strains with potential properties as oral probiotics, namely for the prevention of dental caries. We examined 23 dairy microorganisms, out of which we identified two Streptococcus thermophilus and two Lactcoccus lactis strains that were able to adhere to saliva-coated hydroxyapatite beads to the same extent as Streptococcus sobrinus OMZ176. Two of them, Strep. thermophilus NCC1561 and Lactoc. lactis ssp. lactis NCC2211, were further successfully incorporated into a biofilm mimicking the dental plaque. Furthermore, they could grow in such a biofilm together with five strains of oral bacterial species, representative of supragingival plaque. In this system, Lactoc. lactis NCC2211 was able to modulate the growth of the oral bacteria, and in particular to diminish the colonization of Streptococcus oralis OMZ607, Veillonella dispar OMZ493, Actinomyces naeslundii OMZ745 and of the cariogenic Strep. sobrinus OMZ176. These findings encourage further research with selected non-pathogenic dairy bacterial strains with the aim to decrease the cariogenic potential of dental plaque.

Particulate Bioglass reduces the viability of bacterial biofilms formed on its surface in an in vitro model

45S5 Bioglass is a bioactive implant material which, in its particulate form, is used in the repair of periodontal defects. The surface reactions undergone by this material in an aqueous environment may exert an antibacterial effect that would be beneficial to periodontal surgical treatment. Biofilms of Streptococcus sanguis, an early plaque former, and mixed species biofilms from a salivary inoculum grown under conditions similar to those associated with periodontal implants, were grown on particulate Bioglass in a constant depth film fermenter (CDFF). Control biofilms were grown on inert glass particulates. At sample times of 3, 24 and 48 hours the viability of biofilms of S. sanguis grown on Bioglass was significantly lower than for those grown on inert glass. In the experiments with subgingivally-modelled mixed species biofilms, the total anaerobic counts were significantly lower on Bioglass after 24 and 48 hours, but not 96 or 168 hours, compared to inert glass. Thus, particulate Bioglass has the potential to reduce bacterial colonisation of its surface in vivo, a feature relevant to post-surgical periodontal wound healing.

Supragingival and subgingival microbiota of adult patients with Down's syndrome. Changes after periodontal treatment

In this longitudinal study, five adult Down's syndrome patients with periodontitis were placed on a frequent recall visit schedule (every 6 weeks) after treatment, in order to investigate: 1) the microbiological status, both supragingivally and subgingivally, and the changes that occurred after treatment and 2) the effect of frequent professional supragingival plaque control on the subgingival microbiota and clinical variables in these patients. The clinical variables recorded were probing pocket depth, probing attachment level, bleeding on probing and presence of plaque (full mouth, six surfaces per tooth). Microbiological examination was performed separately for supragingival and subgingival samples from the same site for 14 species, using whole genomic DNA probes and the "checkerboard" DNA-DNA hybridization technique. The findings indicate that, although a reduction of periodontal indices was noticed, plaque levels remained high (60%) even at the end of the experimental period. Periodontal pathogens including Porphyromonas gingivalis, Bacteroides forsythus and Actinobacillus actinomycetemcomitans were frequently detected both supragingivally and subgingivally (>30%). The presence of a species supragingivally and the presence at the same time points subgingivally were correlated. This finding suggested that supragingival plaque acts as a reservoir for reinfection of treated sites. A reduction of the percentages of detection of these species was noticed 1 month after an oral hygiene period as well as at 3 and 6 months after treatment. Inadequate oral hygiene as performed by these patients probably affected supragingival, and consequently subgingival, plaque composition.

Spatial arrangements and associative behavior of species in an in vitro oral biofilm model

The spatial arrangements and associative behavior of Actinomyces naeslundii, Veillonella dispar, Fusobacterium nucleatum, Streptococcus sobrinus, and Streptococcus oralis strains in an in vitro model of supragingival plaque were determined. Using species-specific fluorescence-labeled antibodies in conjunction with confocal laser scanning microscopy, the volumes and distribution of the five strains were assessed during biofilm formation. The volume-derived cell numbers of each strain correlated well with respective culture data. Between 15 min and 64 h, populations of each strain increased in a manner reminiscent of batch growth. The microcolony morphologies of all members of the consortium and their distributions within the biofilm were characterized, as were interspecies associations. Biofilms formed 15 min after inoculation consisted principally of single nonaggregated cells. All five strains adhered strongly to the saliva-conditioned substratum, and therefore, coadhesion played no role during the initial phase of biofilm formation. This observation does not reflect the results of in vitro coaggregation of the five strains, which depended upon the nature of the suspension medium. While the possibility cannot be excluded that some interspecies associations observed at later stages of biofilm formation were initiated by coadhesion, increase in bacterial numbers appeared to be largely a growth phenomenon regulated by the prevailing cultivation conditions.

Validation of an in vitro biofilm model of supragingival plaque

The study of biofilm structure and function mandates the use of model systems for which a host of environmental variables can be rigorously controlled. We describe a model of supragingival plaque containing Actinomyces naeslundii, Veillonella dispar, Fusobacterium nucleatum, Streptococcus sobrinus, and Streptococcus oralis wherein cells are cultivated anaerobically in a saliva-based medium on hydroxyapatite discs coated with a salivary pellicle, with material and pieces of apparatus common to all microbiology laboratories. After 0.5 hr, 16.5 hrs, 40.5 hrs, and 64.5 hrs, the composition of adherent biofilms was analyzed by culture techniques, live/dead fluorescence staining, and confocal laser scanning microscopy. Repeated independent trials demonstrated the repeatability of biofilm formation after 40.5 hrs and 64.5 hrs. Brief exposures of biofilms to chlorhexidine or Triclosan produced losses in viability similar to those observed in vivo. This biofilm model should prove very useful for pre-clinical testing of prospective anti-plaque agents at clinically relevant concentrations.

Competition for glucose between Candida albicans and oral bacteria grown in mixed culture in a chemostat

The competition for glucose as a growth-limiting substrate between Candida albicans and a mixed community of oral bacteria was investigated. A chemostat was operated under glucose-limiting and glucose excess conditions at a dilution rate of 0.05/h. A mixed population of oral bacteria was established and after a steady state had been reached the chemostat was inoculated with C. albicans. Seven bacterial species Streptococcus sanguis, S. sobrinus, S. mitis, Lactobacillus casei, Veillonella dispar, Eubacterium saburreum and Fusobacterium nucleatum - were able to establish stable populations under glucose-limiting conditions. The yeast was unable to grow with the bacteria under glucose limitation. Only three bacterial species, S. sobrinus, L. casei and E. saburreum, became established under glucose-excess conditions. C. albicans was also able to become established in the glucose-excess chemostat and could grow and maintain a steady state in a mixed culture with these organisms. L. casei, S. mitis and S. sobrinus had faster glucose consumption rates than C. albicans. All the bacteria, except for E nucleatum, had maximum specific growth rates higher than C. albicans. The results suggest that glucose may act as a growth-limiting substrate for C. albicans in the establishment and growth of the yeast in a mixed community of oral bacteria.

Effect of an essential oil-containing dentifrice on dental plaque microbial composition

PURPOSE

To determine the effect of 6 months use of an essential oil-containing (EO) antiplaque/antigingivitis fluoride dentifrice on the balance of the oral microbial flora and on the emergence of resistant microbial forms by analysis of dental plaque and saliva.

MATERIALS AND METHODS

The dentifrice essential oils consisted of a fixed combination of thymol, menthol, methyl salicylate, and eucalyptol. An identical fluoride-containing dentifrice without the essential oils served as the control. A subgroup of 66 subjects from a clinical trial population of 321 was randomly selected for characterization of their dental plaque microflora. Saliva was also cultured to monitor for the emergence of opportunistic pathogens. Supragingival plaque and saliva were harvested at baseline, after which subjects received a dental prophylaxis. Subjects were sampled again after 3 and 6 months of product use prior to clinical examination. Plaque was characterized for microbial content by phase contrast microscopy for recognizable cellular morphotypes and by cultivation on nonselective and selective culture media. Determination of the minimum inhibitory concentrations of the test agent against selected Actinomyces and Veillonella isolated bacterial species was conducted at all time points to monitor for the potential development of bacterial resistance.

RESULTS

There were no statistically significant differences between the microbial flora obtained from subjects using the essential oil-containing dentifrice and the vehicle control for all parameters and time periods except for the percentage of spirochetes at 6 months and for percentage of "other" microorganisms at 3 months. The EO group exhibited a lower adjusted mean for both parameters. Additionally, there was no evidence of the development of bacterial resistance to the antimicrobial activity of the essential oils or the emergence of opportunistic pathogens.

Analysis of pH-driven disruption of oral microbial communities in vitro

Previously, a mixed culture chemostat system was used to demonstrate that the pH generated from carbohydrate metabolism, rather than carbohydrate availability per se, was responsible for the shifts observed in the oral microflora which are associated with high carbohydrate diets and the development of dental caries. The aim of this study was to determine more accurately the microbially generated pH at which such shifts occurred. Nine oral bacteria were grown in three independent chemostats, and pulsed with glucose on 10 consecutive days. In one chemostat, pH control was discontinued for 6 h, and the pH fall was restricted to a minimum value of pH 5.5; the pH fall was arrested in the other two chemostats at either pH 5. 0, or at pH 4.5. When the pH was allowed to fall, the numbers and proportions of Streptococcus mutans and Lactobacillus rhamnosus increased; this increase was directly related to the magnitude of the pH fall. Veillonella dispar was the most numerous organism following all glucose pulsing regimes, especially at low pH. The increase in proportions of acidogenic bacteria was accompanied by a fall in the proportions of acid-sensitive species (Fusobacterium nucleatum, Prevotella nigrescens, Streptococcus gordonii and Streptococcus oralis). The counts of these species were relatively stable between pH 5.5 and 4.5, but were markedly reduced when the pH fell below pH 4.5; Neisseria subflava could not persist in the culture at pH 4.5 or below. The data suggest that the disruption of communities associated with glucose metabolism and low pH can be explained in terms of a two-stage process. A fall in pH to a value between pH 5.5 and 4.5 may allow the enrichment of potentially cariogenic species, whilst permitting species associated with health to remain relatively unaffected. A further reduction in pH (<pH 4.5) may not only enhance the competitiveness of odontopathogens, but inhibit the growth and metabolism of non-caries-associated species. The results also indicate that species other that mutans streptococci or lactobacilli are competitive at pH values low enough to demineralise enamel, and thus suggest that a broader range of micro-organisms may be associated with caries initiation.

"Checkerboard" assessments of periodontal microbiota and serum antibody responses: a case-control study

BACKGROUND

We explored the association between subgingival microbial profiles and serum IgG responses to periodontal microbiota in relation to clinical periodontal status.

METHODS

One hundred thirty-one (131) periodontitis patients aged 29 to 74 years (mean 51.8) were age- and gender-matched with 74 periodontally intact controls (range 26 to 77, mean 49.3). Smoking habits and health history were recorded and assessments of plaque, bleeding on probing, probing depth, and attachment level were performed at 6 sites per tooth on all present teeth, excluding third molars. Subgingival plaque samples were obtained from each tooth in one upper and one lower quadrant (maximum 14 samples/subject; 2,440 samples total) and analyzed with respect to 19 species by means of whole genomic DNA probes. Serum IgG antibodies against the same 19 species were assessed by an immunoassay.

RESULTS

Cases displayed an average of 22.7 teeth, 20.3 sites with probing depth > or =6 mm, and 18.9 sites with attachment loss > or =6 mm. Corresponding figures for controls were 27.1, 0.1, and 1.0, respectively. Heavy smoking was 3 times more frequent among cases than controls (32.1% versus 9.6%). Higher levels of Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia, Prevotella nigrescens, Prevotella melaninogenica, Bacteroides forsythus, Fusobacterium nucleatum, Treponema denticola, Eubacterium nodatum, Peptostreptococcus micros, and Campylobacter rectus were found in cases and higher levels of Eikenella corrodens, Veillonella parvula, and Actinomyces naeslundii in controls. Cases displayed higher IgG levels against P. gingivalis and Actinobacillus actinomycetemcomitans, while controls displayed higher levels against F. nucleatum, T. denticola, E. nodatum, and Capnocytophaga ochracea. Positive correlations between bacterial colonization and antibody responses were identified for 9 species in controls. In cases, however, statistically significant correlations were observed for only 3 species out of which only one was positive (V. parvula). Both bacterial levels and antibody responses declined in ages over 55 years. A logistic regression employing selected elements of bacterial colonization and antibody responses as independent variables resulted in 81.1% correct diagnosis, with sensitivity of 83.1%, specificity of 77.8%, positive predictability of 86%, and negative predictability of 73.7%. Smoking did not reach statistical significance in this model.

CONCLUSION

A combined microbial colonization/antibody response profile can effectively discriminate between periodontitis patients and periodontally intact controls.

Development of an anaerobic bacterial leakage model

The majority of bacteria associated with infections of endodontic origin are strict anaerobes. The purpose of this study was to develop an endodontic microleakage model using strict anaerobic bacteria in a two-chamber system. Nine species of anaerobic bacteria were tested for viability and detection by either turbidity or color change of the broth. A survey of pH chromogenic substrates revealed that bromcresol purple (pH 5.2 = yellow, pH 6.8 = purple) could be used as a chromogenic indicator to detect the growth of anaerobic bacteria. Peptone-yeast extract-glucose broth (PYG) and brain heart infusion broth (BHI) were each used alone and with bromcresol purple (bpPYG, bpBHI) in this study. Fusobacterium nucleatum and F. necrophorum were viable in all four media for > 2 wk and produced both turbidity and a color change after only 1 day of incubation. Veillonella parvula in either bpBHI or BHI and Peptostreptococcus anaerobius in either bpPYG or BHI were viable for > 2 wk and showed a color change or turbidity after 1 or 2 days. The results indicate that leakage of strict anaerobes may be evaluated in a two-chamber system.

The establishment of a community of oral bacteria that controls the growth of Candida albicans in a chemostat

The purpose of this study was to establish and identify a community of oral bacteria that controls the growth of Candida albicans in the chemostat. The chemostat was operated under glucose-limiting conditions at a dilution rate of 0.05 h-1 and inoculated with a yeast-free suspension of a tongue scraping. After a steady state had been reached, it was inoculated with C. albicans to establish the yeast and determine whether its growth could be contained. The steady-state community comprised the species Streptococcus sanguis, Streptococcus sobrinus, Streptococcus mitis, Lactobacillus casei, Eubacterium saburreum, Veillonella dispar and Fusobacterium nucleatum. Bacteroides gracilus and Haemophilus segnis were also detected but infrequently. Yeast growth was suppressed and yeast cells were lost at the same rate as the theoretical washout rate. It is concluded that this mixed community of oral bacteria can be used to identify the parameters that maintain the equilibrium between oral bacteria and C. albicans in the oral cavity.

Effects of sublethal exposure to an antiseptic mouthrinse on representative plaque bacteria

Although the mechanism responsible for the clinical antiplaque efficacy of oral antiseptics is generally considered to be primarily one of bactericidal activity, it has been suggested that oral antiseptics may have additional effects on bacteria exposed to sublethal levels. Studies reported herein, investigated the effects of sublethal levels of an essential oil-containing antiseptic mouthrinse (Listerine Antiseptic, Warner-Lambert Co., Morris Plains, NJ) on selected activities of representative plaque microorganisms using in vitro models. These studies demonstrated that sublethal exposure to the tested oral antiseptic can have significant effects in reducing intergeneric coaggregation, increasing bacterial generation time, and extracting endotoxin from Gram-negative bacteria. These in vitro activities can be correlated with features of plaque formation and pathogenicity seen in vivo; however, additional studies will be necessary to confirm that these mechanisms are, in fact, operative clinically.

Adherence, accumulation, and cell division of a natural adherent bacterial population

Developing dental bacterial plaques formed in vivo on enamel surfaces were examined in specimens from 18 adult volunteers during the first day of plaque formation. An intraoral model placing enamel pieces onto teeth was used to study bacterial plaque populations developing naturally to various cell densities per square millimeter of surface area of the enamel (W. F. Liljemark, C. G. Bloomquist, C. L. Bandt, B. L. Philstrom, J. E. Hinrichs, and L. F. Wolff, Oral Microbiol. Immunol. 8:5-15, 1993). Radiolabeled nucleoside incorporation was used to measure DNA synthesis concurrent with the taking of standard viable cell counts of the plaque samples. Results showed that in vivo plaque formation began with the rapid adherence of bacteria until ca. 12 to 32% of the enamel's salivary pellicle was saturated (ca. 2.5 x 10(5) to 6.3 x 10(5) cells per mm2). The pioneer adherent species were predominantly those of the "sanguis streptococci." At the above-noted density, the bacteria present on the salivary pellicle incorporated low levels of radiolabeled nucleoside per viable cell. As bacterial numbers reached densities between 8.0 x 10(5) and 2.0 x 10(6) cells per mm2, there was a small increase in the incorporation of radiolabeled nucleosides per cell. At 2.5 x 10(6) to 4.0 x 10(6) cells per mm2 of enamel surface, there was a marked increase in the incorporation of radiolabeled nucleosides per cell which appeared to be cell-density dependent. The predominant species group in developing dental plaque films during density-dependent growth was the sanguis streptococci; however, most other species present showed similar patterns of increased DNA synthesis as the density noted above approached 2.5 x 10(6) to 4.0 x 10(6) cells per mm2.

Chemostat flow cell system: an in vitro model for the evaluation of antiplaque agents

We developed an experimental in vitro model of dental plaque to assess the potential efficacy of antiplaque agents. The model used a chemostat, which provided a continuous source of 5 species of oral bacteria grown in an artificial "saliva-like" medium. This mixture was pumped through six flow cells, each containing two types of surfaces on which plaque formed and was subsequently measured. Formation of bacterial plaque on hydroxyapatite surfaces was assessed by measurement of the DNA and protein content of the plaque film. The amount of bacterial plaque formed on germanium surfaces was measured by attenuated total reflectance (ATR/FT-IR) spectroscopy. Plaque viability was also assessed by a fluorescent staining technique. The quantity of plaque formed on both types of surfaces gradually increased with the duration of flow (from 24 to 72 h) through the cells during a 72-hour experimental period. The flow cells were then pulsed with experimental treatment solutions for 30 s, twice daily. Parallel to results of human clinical studies, the model was capable of discriminating among water, a placebo mouthrinse, and an active antimicrobial mouthrinse formulation containing 0.03% triclosan. It therefore offers a valuable alternative to animal model testing and allows for more rapid evaluations under well-controlled experimental conditions.

Effect of proteolytic enzymes on the lysis and growth of oral bacteria

Previous studies have shown increased levels of proteolytic enzymes in affected periodontal sites. The aim of the present investigation was to evaluate the effect of proteolytic environments on the lysis and growth of selected oral bacteria associated with either healthy or diseased periodontal sites. The effect of trypsin, chymotrypsin and proteinase K on cell lysis was determined following incubation with bacteria, whereas the effect of the same proteolytic enzymes on bacterial growth was tested using a disc-plate technique. Overall, gram-positive bacteria appeared to be more resistant to lysis than gram-negative bacteria. The most susceptible bacteria were Actinomyces spp., Eubacterium saburreum, Prevotella intermedia, Capnocytophaga ochracea, Fusobacterium nucleatum, Prevotella loescheii, Treponema denticola and Actinobacillus actinomycetemcomitans. The disc-plate procedure indicated that the growth of Actinomyces spp., E. saburreum, C. ochracea, P. intermedia, P. loescheii, Porphyromonas gingivalis and T. denticola were the most affected, more particularly by chymotrypsin and proteinase K. Interestingly, the growth of F. nucleatum was rather stimulated by proteolytic enzymes. The observations reported in this investigation indicate that specific and general proteolytic activities have the ability to lyse some oral bacterial species and to interfere with their growth. It is suggested that such effects could represent new mechanisms by which the bacterial ecology of subgingival sites may be affected.

The effect of tetronasin and monensin on fermentation, microbial numbers and the development of ionophore-resistant bacteria in the rumen

The Gram-negative rumen bacteria Fibrobacter succinogenes S85, Prevotella ruminicola M384 and Veillonella parvula L59 were grown in media containing successively increasing concentrations of the ionophores, monensin and tetronasin. All three species became more resistant to the ionophore with which they were grown. Increased resistance to one ionophore caused increased resistance to the other, and cross-resistance to another ionophore--lasalocid--and an antibiotic--avoparcin. Recovery of tetronasin-resistant bacteria from the rumen of monensin-fed sheep increased and vice versa, indicating that similar cross-resistance occurred in vivo.

Dental plaque development on defined streptococcal surfaces

Coaggregations between bacterial species have been widely studied in vitro but not in the mouth. A new in vivo assay was used to measure the rate and composition of indigenous plaque formation onto bovine enamel chips covered with a continuous layer of bacteria. Chips were covered with Streptococcus oralis ATCC 10557, which coaggregated with many oral species, or Streptococcus gordonii S7, which did not coaggregate with these oral species, and placed in the mouth for 4 and 24 h. There were no differences in the number of most indigenous bacterial species isolated from the two streptococcal surfaces. However, the number of Actinomyces viscosus as a proportion of total Actinomyces spp. was significantly different on the two surfaces at 24 h. With the exception of Actinomyces naeslundii and A. viscosus removed from the S7 surface, all indigenous species increased significantly in number from 4 to 24 h, irrespective of the streptococcal surface. This study demonstrated that interbacterial coaggregation had only a limited effect on in vivo plaque development. Thus suggesting that environmental factors, growth or other adherence phenomena are dominant in in vivo plaque formation.

Modelling of mixed chemostat cultures of an aerobic bacterium, Comamonas testosteroni, and an anaerobic bacterium, Veillonella alcalescens: comparison with experimental data

A mathematical model of mixed chemostat cultures of the obligately aerobic bacterium Comamonas testosteroni and the anaerobic bacterium Veillonella alcalescens grown under dual limitation of L-lactate and oxygen was constructed. The model was based on Michaelis-Menten-type kinetics for the consumption of substrates, with noncompetitive inhibition of V. alcalescens by O2. The growth characteristics of the aerobic and anaerobic organisms were determined experimentally with pure cultures of the individual species in (oxygen-limited) chemostats. Using these pure-culture data in the model of the mixed culture resulted in a good description of the actual mixed cultures of the two bacteria. In the actual mixed-culture experiments, coexistence of the two species occurred only when the cultures were oxygen limited. With increasing oxygen supply (the actual oxygen concentration in the culture remaining at less than 0.2 microM), the biomass of C. testosteroni increased, whereas that of V. alcalescens decreased. Apparently, C. testosteroni protected V. alcalescens from inhibition by oxygen by maintaining sufficiently low oxygen concentrations. The model calculations indicated that competition between the aerobic and the anaerobic bacterium for common substrates (L-lactate and oxygen) occurred and that the anaerobe was the better competitor. Analysis of the culture fluid indicated that C. testosteroni grew primarily at the expense of the fermentation products of V. alcalescens, i.e., propionate and acetate. The model further indicated that with different values of several growth parameters (e.g., substrate affinity and/or inhibition constants), the affinity of the aerobic organism for oxygen and the sensitivity of the anaerobic organism for oxygen were the most important properties determining the coexistence of these two physiologically different types of bacteria.

Growth yield increase and ATP formation linked to succinate decarboxylation in Veillonella parvula

Veillonella parvula strain 259 (= DSM 2007) was able to grow on a mineral salts medium supplemented with (per litre) 1 g yeast extract, 1 g Tween-80, and 3 mg putrescine.2 HCl, with 6 mM thioglycolate as reductant and lactate as growth substrate. Succinate did not serve as a growth substrate, but when added in conjunction with lactate, it was decarboxylated to propionate and resulted in a measurable increase in growth yield, corresponding to the formation of 2.4 g cell dry mass per mol succinate. A growth yield increase linked to succinate metabolism occurred only while lactate was also being metabolised. Experiments with cell suspensions showed that succinate decarboxylating activity was constitutive. Addition of succinate produced clear increases in cellular ATP levels in ATP-depleted washed cells.

Effect of nutrients on defined bacterial plaques and Streptococcus mutans C67-1 implantation in a model mouth

Actinomyces viscosus WVU 627, Streptococcus oralis LPA-1 and Veillonella dispar OMZ 193 were cocultured on teeth in a model mouth for 66 h. Synthetic saliva containing bovine salivary glycoprotein supported bacterial growth, although the delivery of an intermittent nutrient supplement, containing 1% (w/v) glucose or sucrose, gave greater bacterial cell and viable counts. When Streptococcus mutans C67-1 was super-inoculated onto 24-hour mixed plaques, it became established under all regimens, but there was pronounced colonization resistance. With saliva only, the proportion of S. mutans at 66 h was less than 0.5% of the total cultivable microflora. When a glucose supplement was delivered for 1 h every 6 h, S. mutans attained a final proportion of 2.4%. With sucrose, both S. mutans C67-1 and its non-cariogenic glucan-deficient mutant, C67-25, attained similar proportions of 15-20%. These experiments indicate how this model can be used to study the factors influencing colonizing ability and microbial interactions in biofilms under controlled conditions.

Colonization resistance of defined bacterial plaques to Streptococcus mutans implantation on teeth in a model mouth

We investigated the ability of Streptococcus mutans C67-1 to colonize simple bacterial plaques and the effects of age and stability of the pre-formed plaque on colonization resistance. Mixed-plaques of Actinomyces viscosus WVU627, 'Streptococcus mitior' LPA-1, and Veillonella dispar OMZ193 were grown on tooth segments, mounted back to back for simulation of approximal sites in a model mouth for 66 h. S. mutans C67-1 was either included in the original inoculum or super-inoculated onto the developing plaque. Inclusion of S. mutans C67-1 did not alter the total viable counts, but the proportional composition changed due to inter-species interactions. Colonization resistance of the mixed-plaque samples developed within 24 h, although S. mutans C67-1 was always able to colonize these stagnation sites. Colonization resistance of 24-hour plaque against a fresh isolate, S. mutans CP3, was also studied. There was greater colonization resistance by the basic plaque to this organism, compared with S. mutans C67-1, although the reasons for this were not clear. These initial experiments demonstrate the way in which the factors involved in bacterial colonization resistance in microbial films on teeth can be studied under controlled conditions.

Coaggregation properties of human oral Veillonella spp.: relationship to colonization site and oral ecology

The primary habitats of oral veillonellae are the tongue, dental plaque, and the buccal mucosa. Isolates were obtained from each habitat and tested for coaggregation with a battery of other oral bacterial strains. All 59 tongue isolates tested for coaggregation were Veillonella atypica or Veillonella dispar. All but one of them coaggregated with strains of Streptococcus salivarius, a predominant inhabitant of the tongue surface but not subgingival dental plaque. These tongue isolates were unable to coaggregate with most normal members of the subgingival flora such as Actinomyces viscosus, Actinomyces naeslundii, Actinomyces israelii, and Streptococcus sanguis. In contrast, 24 of 29 Veillonella isolates, of which 20 were Veillonella parvula from subgingival dental plaque samples, coaggregated strongly with the three species of Actinomyces, S. sanguis, and other bacteria usually present in subgingival plaque, but they did not coaggregate with S. salivarius. The majority of isolates from the buccal mucosa (42 of 55) has coaggregation properties like those from the tongue. These results indicate that the three human oral Veillonella species are distributed on oral surfaces that are also occupied by their coaggregation partners and thus provide strong evidence that coaggregation plays a critical role in the bacterial ecology of the oral cavity.

Fermentation products, amino acid utilization, maintenance energies and growth yields for the fibrillar Streptococcus salivarius HB and a non-fibrillar mutant HB-B grown in continuous culture under glucose limitation

The fibrillar strain Streptococcus salivarius HB and a non-fibrillar mutant, strain HB-B, were grown in a defined medium under glucose limitation in a chemostat. Fermentation balances were produced for both strains in batch culture and at growth rates between 0.1/h and 1.1/h. In batch culture both strains fermented glucose to lactate, but in continuous culture glucose was fermented to formate, acetate and ethanol with increasing amounts of lactate as the growth rate was increased. Lactate never became the major fermentation product even at the highest growth rate. Amino acid analysis showed that only lysine was more than 50% utilized, while proline and tyrosine showed net production. The non-fibrillar strain HB-B showed, in general, a reduced utilization of amino acids compared with the fibrillar strain HB. Calculated growth yields and maintenance energies for the two strains showed that there was a reduction in the true growth yield and the maintenance energy coefficient of the non-fibrillar strain HB-B when compared with the fibrillar strain HB. The increase in the maintenance energy of the fibrillar strain HB (1.382 mmol/g/h) when compared with the non-fibrillar strain HB-B (0.546 mmol/g/h) of 153% is proposed to be the energy required for the maintenance of the fibrillar surface of the cell.

Monobacterial and mixed bacterial plaques of Streptococcus mutans and Veillonella alcalescens in an artificial mouth: development, metabolism, and effect on human dental enamel

To gain greater understanding of the role of Streptococcus mutans and Veillonella in the caries process, studies of both aerobically and anaerobically grown plaques of S. mutans C67-1 and V. alcalescens V-1 on human enamel slabs were carried out in an artificial mouth. Plaque development, acid production, and demineralization were measured. Early plaque development of monobacterial and mixed bacterial plaques started from randomly adhering cells on day 1 to confluent multilayered microcolonies on day 4. Differences were observed in viable cell counts, total cell mass, and in acid production. In most cases CFU, DNA and acid production were higher in the mixed bacterial plaque, especially in the anaerobic mixed plaque. Lactic acid was the predominant acid in all cases following the supply of sucrose to the plaque. No decisive role could be found for acetic, formic, and propionic acid. No inhibition of demineralization was observed in the enamel slabs inoculated with both aerobic and anaerobic mixed plaques. Demineralization ranged from the more classical picture of lesion development in the aerobic monobacterial plaque-treated samples to an aggressive etching of the enamel surface in the anaerobically mixed treated slabs.

Early microbial colonization of permucosal implants in edentulous patients

In edentulous patients, the microbial colonization of permucosal implants of sintered hydroxyapatite was studied. Samples were taken from mucosa and dentures before insertion of implants and from supra- and subgingival sites two to 10 weeks after insertion. In total, five patients and 10 implants with clinically healthy peri-implant tissues were studied. The samples were investigated by dark-field microscopy and anaerobic culture. The supragingival plaque of the implants was dominated by Gram-positive cocci and rods, the subgingival plaque by Haemophilus spp. and Veillonella parvula. A group of bacteria was found specifically related to the implants: Actinomyces odontolyticus, Peptostreptococcus micros, Haemophilus actinomycetemcomitans, Eikenella corrodens, Capnocytophaga sputigena, and Leptotrichia buccalis. Black-pigmented Bacteroides was not found in any of the examined samples. Spirochetes were observed in denture plaque samples and in supragingival plaque of the implants. It is concluded that bacteria known as potential periodontal pathogens colonize the permucosal implants in the first weeks after insertion. The presence of these species seems to be dependent on the ecological factors provided by the artificial gingival crevice of the permucosal implants in the edentulous mouth.

Structural specificity of diamines covalently linked to peptidoglycan for cell growth of Veillonella alcalescens and Selenomonas ruminantium

Putrescine and cadaverine are essential constituents of the peptidoglycan of Veillonella alcalescens, Veillonella parvula, and Selenomonas ruminantium and are necessary for the growth of these organisms (Y. Kamio and K. Nakamura, J. Bacteriol. 169:2881-2884, 1987, and Y. Kamio, H. Pösö, Y. Terawaki, and L. Paulin, J. Biol. Chem. 261:6585-6589, 1986). In this study, the structural specificity of the diamine requirement for normal cell growth of these bacteria was examined by using a series of diamines with a general structure of NH3+ X (CH2)n X NH3+. Diaminohexane (n = 6) which was incorporated into the peptidoglycan was as effective as putrescine (n = 4) and cadaverine (n = 5) for normal cell growth. However, diaminopropane (n = 3) and diaminoheptane (n = 7) were less effective for growth than diaminohexane, although they were incorporated into the peptidoglycan to the same extent.

Interactions between rumen amylolytic and lactate-utilizing bacteria in growth on starch

The growth and metabolism of the rumen amylolytic bacteria Streptococcus bovis, Butyrivibrio fibrisolvens and Bacteroides ruminicola, growing in pure cultures and co-cultures with the rumen lactilytic bacteria Megasphaera elsdenii and Veillonella alcalescens were followed. The interaction of amylolytic bacteria with V. alcalescens represents a simple food chain. The interaction with M. elsdenii is more complex, since there is a simultaneous competition for products of the starch degradation.

The establishment of reproducible, complex communities of oral bacteria in the chemostat using defined inocula

Nine commonly isolated oral bacterial populations were inoculated into a glucose-limited and a glucose-excess (amino acid-limited) chemostat maintained at a constant pH 7.0 and a mean community generation time of 13.9 h. The bacterial populations were Streptococcus mutans ATCC 2-27351, Strep. sanguis NCTC 7865, Strep. mitior EF 186, Actinomyces viscosus WVU 627, Lactobacillus casei AC 413, Neisseria sp. A1078, Veillonella alkalescens ATCC 17745, Bacteroides intermedius T 588 and Fusobacterium nucleatum NCTC 10593. All nine populations became established in the glucose-limited chemostat although Strep. sanguis and Neisseria sp. were present only after a second and third inoculation, respectively. In contrast, even following repeated inoculations, Strep. mutans, B. intermedius and Neisseria sp. could not be maintained under glucose-excess conditions. A more extensive pattern of fermentation products and amino acid catabolism occurred under glucose-limited growth; this simultaneous utilization of mixed substrates also contributed to the higher yields (Y molar glucose) and greater species diversity of these communities. Microscopic and biochemical evidence suggested that cell-to-cell interactions and food chains were occurring among community members. To compare the reproductibility of this system, communities were established on three occasions under glucose-limitation and twice under glucose-excess conditions. The bacterial composition of the steady-state communities and their metabolic behaviour were similar when grown under identical conditions but varied in a consistent manner according to the nutrient responsible for limiting growth. Although a direct simulation of the oral cavity was not attempted, the results show that the chemostat could be used as an environmentally-related model to grow complex but reproducible communities of oral bacteria for long periods from a defined inoculum.

Bacteriology of experimental gingivitis in young adult humans

From replicate trials of experimental gingivitis in four periodontally healthy subjects, 166 bacterial species and subspecies were detected among 3,034 randomly selected isolates from 96 samples. Of these bacteria, Actinomyces naeslundii (serotype III and phenotypically similar strains that were unreactive with available antisera), Actinomyces odontolyticus (serotype I and phenotypically similar strains that were unreactive with available antisera), Fusobacterium nucleatum, Lactobacillus species D-2, Streptococcus anginosus, Veillonella parvula, and Treponema species A appeared to be the most likely etiological agents of gingivitis. Statistical interpretations indicated that the greatest source of microbiological variation of the total flora observed was person-to-person differences in the floras. The next greatest source of variation was the inflammatory status of the sample sites. Person-to-person differences were smallest at experimental day 4. The floras became more diverse with time and as gingivitis developed and progressed. Analyses indicated that sequential colonization by certain species was repeatable and therefore probably predictable. Variation was relatively small between replicate trials, between two sites on the same teeth sampled on the same day, and between the same sites sampled at the same relative time in a replicate trial.

Effect of microbial interaction on the colonization rate of Actinomyces viscosus or Streptococcus mutans in the dental plaque of rats

The resident oral microflora of conventional Osborne-Mendel rats was challenged with Actinomyces viscosus or Streptococcus mutans strains. The adherence of the inoculated organism to the tooth surface and the subsequent growth were studied by means of viable counts determination. The initial growth rate of S. mutans in conventional rats was lower than in mono-associated gnotobiotic rats (doubling time, td = 5 h versus td = 1.1 h). The delayed start of growth and the low initial growth rate indicated that a competitive interaction between S. mutans and the resident microflora occurred. The initial growth rate of A. viscosus in conventional rats (td = 3.1 h) was approximately the same as that in gnotobiotic rats (td = 2.8 h). The start of growth of A. viscosus was only slightly delayed compared with the start in gnotobiotic rats. These results suggest a neutralistic relationship between A. viscosus and the resident microflora. A. viscosus reached a stationary level about 7 days after inoculation, whereas the S. mutans strains did not reach stationary levels until 2 weeks after inoculation.

Microbial populations growing in the presence of fluoride at low pH isolated from dental plaque of children living in an area with fluoridated water

Longitudinal microbiological examinations have been made of dental plaque from a site approximal to the upper central incisors of 10 8-year-old children living in an area with water fluoridation. Differential counts of viable bacteria, made using a selective medium containing various levels of fluoride (0 to 100 mug/ml) at pH levels of 7.0 to 5.5, demonstrated an effect of both pH and fluoride on the numbers and types of bacteria isolated. Strains of Streptococcus and Neisseria grew after only 16 h of incubation at pH levels as low as 6.0 with fluoride levels up to 50 mug/ml. The most commonly isolated streptococci were Streptococcus mitior and S. salivarius. S. mutans was isolated less frequently and was inhibited by 20 and 50 mug of fluoride per ml at pH 6.0 and 6.5, respectively. Veillonella strains were the most resistant isolates, being isolated after 16 h of incubation on media at pH 6.0 with 100 mug of fluoride per ml. Despite their known fluoride resistance, Actinomyces spp. were often only detected on the selective media after 72 h of incubation. The pH of the medium had a definite selective effect, as the number of colonies growing on the fluoride-free basal media at pH 6.0 was only 30% of that at pH 7.0. Representative strains of S. mutans, S. mitior, S. sanguis, and S. milleri were tested for their ability to utilize glucose at the pH and fluoride levels of the medium on which they were initially isolated. Fluoride reduced the initial glycolytic rate of the cells, but in 5 of the 13 strains tested the final amount of glucose used after 2 h of incubation was the same in the presence or absence of fluoride. The isolation of bacteria capable of growth in the presence of fluoride over a significant portion of the pH range that occurs in plaque in vivo could explain in part the finding that fluoride does not have a dramatic effect on the plaque community. Fluoride in plaque may reduce the ecological advantage afforded to aciduric S. mutans strains by carbohydrate substances. In the in vivo situation this could mean that, even with high carbohydrate intake, fluoride may permit S. mitior to compete with S. mutans within the plaque ecosystem.

Effects of growth temperature on fatty acid and alk-1-enyl group compositions of Veillonella parvula and Megasphaera elsdenii phospholipids

Veillonella parvula ATCC 10790, an anaerobic gram-negative coccus, contains diacyl and alk-1-enyl acyl (plasmalogen) forms of phosphatidylethanolamine and phosphatidylserine. We studied the effect of growth temperature on the lipid composition of this strain. There was a small increase in the phosphatidylethanolamine content but no change in the content of plasmalogens at the lower growth temperatures tested. The total acyl chains and the plasmalogen acyl chains contained between 73 and 80% mono-unsaturated fatty acids at all growth temperatures. The plasmalogen alk-1-enyl chains were significantly more unsaturated in cells grown at 30 and 25 degrees C than in cells grown at 37 degrees C. Differential scanning calorimetry of the hydrated phospholipids showed lower phase transition temperatures for the lipids from the cells grown at the lower temperatures. In Megasphaera elsdenii lipids, which are similar in composition to the lipids of V. parvula, the proportion of phosphatidylethanolamine also increased slightly at lower growth temperatures, with no significant change in the content of plasmalogens. M. elsdenii contained cyclopropane fatty acyl and alk-1-enyl chains in addition to the mono-unsaturated and saturated chains previously reported. As cells entered the stationary phase of growth at 30 and 42.5 degrees C, there was a reciprocal increase in the proportion of cyclopropane acyl chains and decrease in the unsaturated moieties. The total proportion of cyclopropane and unsaturated acyl and alk-1-enyl chains was more than 65% at all growth temperatures studied, and there was no discernible increase in the sum of these moieties at the lower growth temperatures.

Selective antibacterial properties of lysozyme for oral microorganisms

The antibacterial properties of lysozyme were investigated with oral microorganisms representing the seven serotypes (a through g) of Streptococcus mutans, Veillonella alcalescens, and the virulent (V) and avirulent (AV) strains of Actinomyces viscosus T14. Growth of bacteria in defined medium was monitored spectrophotometrically after the addition of various amounts (25 mug to 5 mg/ml) of enzyme. No growth inhibition of V. alcalescens was observed. Inhibition of A. viscosus T14(V) and A. viscosus T14(AV) occurred with 160 mug of lysozyme per ml. Of the S. mutans cultures tested, the serotype a and b strains were inhibited with as little as 25 mug of enzyme per ml, whereas e and f strains were most resistant to the bacteriostatic activity of lysozyme. The presence of dl-threonine or sucrose in growth medium did not significantly affect the results. A lysoplate assay was developed to rapidly survey the bacterial cultures for their susceptibility to the lytic ability of the enzyme. Lysis, as a measure of a zone of clearing in agarose plates, occurred for all microorganisms in the presence of lysozyme after the subsequent addition of NaCl or detergent. The bactericidal activity of lysozyme was determined on S. mutans BHT and S. mutans LM-7 by the pour plate technique. Preincubation of S. mutans LM-7 with as much as 1 mg of enzyme for 90 min did not affect viability or growth, whereas preincubation of S. mutans BHT with 1 mg of lysozyme resulted in no recoverable colony-forming units. An antigen containing extract of S. mutans LM-7 blocked the growth inhibitory property of lysozyme. Human lysozyme was a more effective antibacterial factor than hen egg white lysozyme. Total growth inhibition of S. mutans BHT was effected with 40 mug of human enzyme, and as little as 10 mug of human enzyme inhibited growth for greater than 20 h. The data presented indicate that different mechanisms may be responsible for the bacteriostatic, lytic, and bactericidal properties of the enzyme and that lysozyme is a selective but effective antibacterial factor for oral microorganisms.

Faecal flora of South Indian infants and young children in health and with acute gastroenteritis

The faecal flora of 29 healthy infants and young children was compared with that of 49 children of similar age and socio-ecomonic status with acute gastroenteritis. In the healthy children the most common organisms in the faeces were bifidobacteria, veillonellae, enterobacteria and enterodocci with anaerobes outnumbering aerobes. Most members of the noraml faecal flora were present in the diarrhoeal stools, but anaerobes were signigicantly reduced in number and enterobacteria were significantly increased, thereby altering the ratio of anaerobes to aerobes. The alterations in the flora were not related to the nature of the aetiological agent or to the severity of the diarrhoea. The changes appeared to be a direct result of the altered colonic environment produced by the diarrhoeal state. In 13 of the 28 patients from whom bacterial pathogens were isolated, the pathogens were the predominant faecal organsims.

Adherence of Veillonella species mediated by extracellular glucosyltransferase from Streptococcus salivarius

The effect of extracellular products from Streptococcus salivarius on sucrose-dependent adherence to smooth surfaces by other oral bacteria was studied in vitro. Strains of Streptococcus mitis, Streptococcus pyogenes, and Veillonella parvula without innate ability to adhere to a steel wire were able to do so when incubated with sucrose and cell-free culture fluid from S. salivarius strains 9759, 25975, CNII, and MEPI. These culture fluids synthesized more adherent material and water-insoluble glucan than those from Streptococcus mutans C67-1 and seven other S. salivarius strains. Among the S. salivarius strains, glucosyltransferase (GT; dextransucrase, EC 2.4.1.5) activity varied more than 100-fold. Cells of Veillonella and S. mitis S3 that had been incubated in culture fluids from S. salivarius 25975 and 9759, respectively, and then washed adhered upon subsequent incubation with sucrose. This was due to adsorbed GT because (i) the adherence was sensitive to dextranase; (ii) it was observed only with the high-GT culture fluids; (iii) it was dependent on sucrose; and (iv) the washed Veillonella cells synthesized glucan, but not fructan, from sucrose. These results suggest that sucrose-dependent adherence of bacteria without such innate ability can be mediated by (i) entrapment in insoluble glucan synthesized by S. salivarius culture fluids, and (ii) prior adsorption of GT from S. salivarius culture fluids. The possibility that GT formed by high-yield strains of S. salivarius is distributed through the mouth by the action of salivary flow and contributes to sucrose-dependent adherence and plaque formation is considered.

Nitrate-reductase electron-transport cofactors in Veillonella alcalescens

Studies on the effects of inhibitors of the nitrate-reducing activity of Veillonella alcalescens extracts suggest the participation of a naphthoquinone, a b-type cytochrome, and non-heme iron in electron transport to nitrate. A nitrate-reductase-deficient mutant displayed a longer doubling time and a decreased molar growth yield on nitrate media. This mutant was phenotypically restored by the addition of molybdate to the growth medium, giving evidence for the functioning of molybdenum in the nitrate-reductase enzyme of V. alcalescens.