Oral Ecology Research Articles

Oral dysbacteriosis in type 2 diabetes and its role in the progression to cardiovascular disease.

Salivary changes and proliferation of specific bacterial communities are known to result in oral disease which may adversely impact on systemic conditions like diabetes and cardiovascular diseases. This study reports on the changes in oral ecology of healthy and diseased adults and the possible role in disease causation. The study comprised 150 participants divided into control (healthy), diabetic and cardiac groups. After dental examination for (Decayed Missing Filled Teeth (DMFT) and Oral Rating Index (ORI), stimulated saliva was sampled to determine flow rate and buffering capacity. Salivary microbial load of Streptococcus mutans and Lactobacilli were subsequently quantified. DMFT, ORI, buffering capacity and flow rate were inferior for both diabetic and cardiac patients, who had higher bacterial counts (p<0.05). Long standing diabetics harboured a higher load of Streptococcus mutans. The microbial load of Streptococcus mutans in cardiac patients was double that of diabetics. Disruption in the salivary environment and changes in microbial ecology with increased load of cariogenic bacteria were found in diabetic and cardiac patients. This study brings forward new evidence of a markedly higher load of Streptococcus mutans in cardiac patients which may underlie the progression of diabetes to cardiovascular disease in this population.

Evidence for biofilm acid neutralization by baking soda

BackgroundThe generating of acids from the microbial metabolism of dietary sugars and the subsequent decrease in biofilm pH below the pH at which tooth mineral begins to demineralize (critical pH) are the key elements of the dental caries process. Caries preventive strategies that rapidly neutralize biofilm acids can prevent demineralization and favor remineralization and may help prevent the development of sugar-induced dysbiosis that shifts the biofilm toward increased cariogenic potential. Although the neutralizing ability of sodium bicarbonate (baking soda) has been known for many years, its anticaries potential as an additive to fluoride dentifrice has received only limited investigation. Types of Studies ReviewedThere is evidence that baking soda rapidly can reverse the biofilm pH decrease after a sugar challenge; however, the timing of when it is used in relation to a dietary sugar exposure is critical in that the sooner its used the greater the benefit in preventing a sustained biofilm pH decrease and subsequent demineralization. Furthermore, the effectiveness of baking soda in elevating biofilm pH appears to depend on concentration. Thus, the concentration of baking soda in marketed dentifrice products, which ranges from 10% to 65%, may affect their biofilm pH neutralizing performance. People with hyposalivation particularly may benefit from using fluoride dentifrice containing baking soda because of their diminished ability to clear dietary sugars and buffer biofilm acids. ConclusionsAlthough promising, there is the need for more evidence that strategies that modify the oral ecology, such as baking soda, can alter the cariogenic (acidogenic and aciduric) properties of biofilm microorganisms. Practical ImplicationsThe acid neutralization of dental biofilm by using fluoride dentifrice that contains baking soda has potential for helping counteract modern high-sugar diets by rapidly neutralizing biofilm-generated acid, especially in people with hyposalivation.

Design and validation of a DNA-microarray for phylogenetic analysis of bacterial communities in different oral samples and dental implants

The quali-quantitative characterization of the oral microbiota is crucial for an exhaustive knowledge of the oral ecology and the modifications of the microbial composition that occur during periodontal pathologies. In this study, we designed and validated a new phylogenetic DNA-microarray (OralArray) to quickly and reliably characterize the most representative bacterial groups that colonize the oral cavity. The OralArray is based on the Ligation Detection Reaction technology associated to Universal Arrays (LDR-UA), and includes 22 probe sets targeted to bacteria belonging to the phyla Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, Fusobacteria, and Spirochaete. The tool is characterized by high specificity, sensitivity and reproducibility. The OralArray was successfully tested and validated on different oral samples (saliva, lingual plaque, supragingival plaque, and healing cap) collected from 10 healthy subjects. For each specimen, a microbial signature was obtained, and our results established the presence of an oral microbial profile specific for each subject. Moreover, the tool was applied to evaluate the efficacy of a disinfectant treatment on the healing caps before their usage. The OralArray is, thus, suitable to study the microbiota associated with various oral sites and to monitor changes arising from therapeutic treatments.

Evolution of the Oral Microbiome and Dental Caries

Our paper reviews how dietary changes during human evolution have contributed to the increased incidence and prevalence of dental caries in modern populations by shifting the oral microbiome from a “healthy” to “carious” state. We addressed two questions: (1) what is the microbial difference between the states of health and caries, and (2) how has the development of an agricultural diet impacted the oral microbiome? The application of next-generation sequencing has revealed the complexity of the oral microbiome and lack of a simple compositional difference between health and caries. Genetic analysis of the oral microbiome from contemporary and ancient humans has shown that the introduction of agriculture was associated with increased frequency of caries-related bacteria and the evolution of the key carious pathogen, Streptococcus mutans. The adoption of an agricultural diet has contributed to a modern rise in caries by changing the oral microbiome ecology. Identification of evolutionary factors that have influenced the oral microbiome in health and caries, and how the two states differ functionally, as opposed to compositionally, may help to reduce the current burden of caries.

Effect of arginine on the growth and biofilm formation of oral bacteria

BackgroundAlkali production via arginine deiminase system (ADS) of oral bacteria plays a significant role in oral ecology, pH homeostasis and inhibition of dental caries. ADS activity in dental plaque varies greatly between individuals, which may profoundly affect their susceptibility to caries. ObjectiveTo investigate the effect of arginine on the growth and biofilm formation of oral bacteria. Methods and resultsPolymicrobial dental biofilms derived from saliva were formed in a high-throughput active attachment biofilm model and l-arginine (Arg) was shown to reduce the colony forming units (CFU) counts of such biofilms grown for various periods or biofilms derived from saliva of subjects with different caries status. Arg hardly disturbed bacterial growth of Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinis and Streptococcus gordonii in BHI medium, but only inhibited biofilm formation of S. mutans. Scanning electron microscope (SEM) showed S. mutans biofilms harboured fewer cells grown with Arg than that without Arg, even in the initial 2h and 8h phase. Confocal laser scanning microscope (CLSM) images of poly-microbial dental and S. mutans biofilms revealed the biofilms grown with Arg had lower exopolysaccharide (EPS)/bacteria ratios than those without Arg (P=0.004, 0.002, respectively). Arg could significantly reduce the production of water-insoluble EPS in S. mutans biofilms (P<0.001); however, quantitative real-time PCR (qRT-PCR) did not show significantly influence in gene expression of gtfB, gtfC or gtfD (P=0.32, 0.06, 0.44 respectively). ConclusionsArg could reduce the biomass of poly-microbial dental biofilms and S. mutans biofilms, which may be due to the impact of Arg on water-insoluble EPS. Considering the contribution to pH homeostasis in dental biofilms, Arg may serve as an important agent keeping oral biofilms healthy thus prevent dental caries.

A randomised clinical study to determine the effect of a toothpaste containing enzymes and proteins on plaque oral microbiome ecology

The numerous species that make up the oral microbiome are now understood to play a key role in establishment and maintenance of oral health. The ability to taxonomically identify community members at the species level is important to elucidating its diversity and association to health and disease. We report the overall ecological effects of using a toothpaste containing enzymes and proteins compared to a control toothpaste on the plaque microbiome. The results reported here demonstrate that a toothpaste containing enzymes and proteins can augment natural salivary defences to promote an overall community shift resulting in an increase in bacteria associated with gum health and a concomitant decrease in those associated with periodontal disease. Statistical analysis shows significant increases in 12 taxa associated with gum health including Neisseria spp. and a significant decrease in 10 taxa associated with periodontal disease including Treponema spp. The results demonstrate that a toothpaste containing enzymes and proteins can significantly shift the ecology of the oral microbiome (at species level) resulting in a community with a stronger association to health.

Candida albicans alters the bacterial microbiome of early in vitro oral biofilms

ABSTRACTThe yeast Candida albicans is an oral commensal microorganism, occurring in the oral cavity of 50–70% of healthy individuals. Its effect on oral ecology has mostly been studied using dual-species models, which disregards the complex nature of oral biofilms. The aim of this study was to culture C. albicans in a complex model to study its effect on oral biofilms. Biofilms, inoculated using pooled stimulated saliva with or without addition of C. albicans, were grown under anaerobic, aerobic, or aerobic +5% CO2 conditions. Red autofluorescence was quantified using a spectrophotometer and visualized in fluorescence photographs. The microbiome of 5 h biofilms was determined using 16S rDNA sequencing. C. albicans was only able to proliferate in biofilms grown under aerobic conditions. After 48 h, C. albicans did not induce differences in total biofilm formation, lactic acid accumulation (cariogenic phenotype) or protease activity (periodontitis phenotype). In vitro, anaerobically grown biofilms developed red autofluorescence, irrespective of inoculum. However, under aerobic conditions, only C. albicans–containing biofilms showed red autofluorescence. Facultative or strict anaerobic Veillonella, Prevotella, Leptotrichia, and Fusobacterium genera were significantly more abundant in biofilms with C. albicans. Biofilms without C. albicans contained more of the aerobic and facultative anaerobic genera Neisseria, Rothia, and Streptococcus. The presence of C. albicans alters the bacterial microbiome in early in vitro oral biofilms, resulting in the presence of strictly anaerobic bacteria under oxygen-rich conditions. This in vitro study illustrates that C. albicans should not be disregarded in healthy oral ecosystems, as it has the potential to influence bacteria significantly.

Transmission of viruses via our microbiomes.

BackgroundBacteria inhabiting the human body have important roles in a number of physiological processes and are known to be shared amongst genetically-related individuals. Far less is known about viruses inhabiting the human body, but their ecology suggests they may be shared between close contacts.ResultsHere, we report the ecology of viruses in the guts and mouths of a cohort and demonstrate that substantial numbers of gut and oral viruses were shared amongst genetically unrelated, cohabitating individuals. Most of these viruses were bacteriophages, and each individual had distinct oral and gut viral ecology from their housemates despite the fact that some of their bacteriophages were shared. The distribution of bacteriophages over time within households indicated that they were frequently transmitted between the microbiomes of household contacts.ConclusionsBecause bacteriophages may shape human oral and gut bacterial ecology, their transmission to household contacts suggests they could have substantial roles in shaping the microbiota within a household.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-016-0212-z) contains supplementary material, which is available to authorized users.

Nitrate and the Origin of Saliva Influence Composition and Short Chain Fatty Acid Production of Oral Microcosms.

Nitrate is emerging as a possible health benefactor. Especially the microbial conversion of nitrate to nitrite in the oral cavity and the subsequent conversion to nitric oxide in the stomach are of interest in this regard. Yet, how nitrate influences the composition and biochemistry of the oral ecosystem is not fully understood. To investigate the effect of nitrate on oral ecology, we performed a 4-week experiment using the multiplaque artificial mouth (MAM) biofilm model. This model was inoculated with stimulated saliva of two healthy donors. Half of the microcosms (n = 4) received a constant supply of nitrate, while the other half functioned as control (n = 4). Additionally, all microcosms received a nitrate and sucrose pulse, each week, on separate days to measure nitrate reduction and acid formation. The bacterial composition of the microcosms was determined by 16S rDNA sequencing. The origin of the saliva (i.e., donor) showed to be the strongest determinant for the development of the microcosms. The supplementation of nitrate was related to a relatively high abundance of Neisseria in the microcosms of both donors, while Veillonella was highly abundant in the nitrate-supplemented microcosms of only one of the donors. The lactate concentration after sucrose addition was similarly high in all microcosms, irrespective of treatment or donor, while the concentration of butyrate was lower after nitrate addition in the nitrate-receiving microcosms. In conclusion, nitrate influences the composition and biochemistry of oral microcosms, although the result is strongly dependent on the inoculum.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-016-0775-z) contains supplementary material, which is available to authorized users.

A novel compound to maintain a healthy oral plaque ecology in vitro

ObjectiveDental caries is caused by prolonged episodes of low pH due to acid production by oral biofilms. Bacteria within such biofilms communicate via quorum sensing (QS). QS regulates several phenotypic biofilm parameters, such as biofilm formation and the production of virulence factors. In this study, we evaluated the effect of several QS modifiers on growth and the cariogenic potential of microcosm oral biofilms.MethodsBiofilms were inoculated with pooled saliva and cultured in the presence of sucrose for 48 and 96 h. QS modifiers (or carrier controls) were continuously present. Lactic acid accumulation capacities were compared to evaluate the cariogenic potential of the biofilms. Subsequently, biofilm growth was quantified by determining colony forming unit counts (CFUs) and their ecology by 16S rDNA-based microbiome analyses. The minimal inhibitory concentration (MIC) for several Streptococcus spp. was determined using microbroth dilution.ResultsOf the tested QS modifiers only 3-oxo-N-(2-oxocyclohexyl)dodecanamide (3-Oxo-N) completely abolished lactic acid accumulation by the biofilms without affecting biofilm growth. This compound was selected for further investigation. The active range of 3-Oxo-N was 10–100 µM. The homologous QS molecule, acyl homoserine lactone C12, did not counteract the reduction in lactic acid accumulation, suggesting a mechanism other than QS inhibition. Microbial ecology analyses showed a reduction in the relative abundance of Streptococcus spp. in favor of the relative abundance of Veillonella spp. in the 3-Oxo-N exposed biofilms. The MIC of 3-Oxo-N for several streptococcal species varied between 8 and 32 µM.Conclusion3-Oxo-N changes the ecological homeostasis of in vitro dental plaque. It reduces its cariogenic potential by minimizing lactic acid accumulation. Based on our in vitro data, 3-Oxo-N represents a promising compound in maintaining a healthy, non-cariogenic, ecology in in vivo dental plaque.

Antimicrobial Efficacy of Salvadora persica Extracts on a Monospecies Biofilm on Orthodontic Brackets In Vitro.

The oral cavity is a rich ecosystem with a plethora of microorganisms, and different components of fixed orthodontic appliances may contribute to a shift in the balance of oral ecology. The purpose of this study was to investigate the antimicrobial potential of hexane and ethanol extracts of Salvadora persica on a monospecies biofilm model established on orthodontic brackets in vitro. Streptococcus mutans biofilm was formed on mini diamond orthodontic brackets following three days of anaerobic incubation at 37˚C. The bacterial cell viability of this biofilm was measured after their exposure to saline, hexane extract of S. persica, ethanol extract of S. persica and 0.2% chlorhexidine using 3-(4, 5-dimethylthiazol- 2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium (MTS) assay. On half of the brackets, the colony forming units (CFU) were counted. Both experiments were performed in triplicate. The absorbance values obtained from the MTS reduction assay after exposure to the different test agents showed a decline in the bacterial cell viability of the S. mutans biofilm as follows: chlorhexidine (+)<hexane extract (S. persica, 5 mg/ml)<ethanol extract (S. persica, 5 mg/ml)<saline+2% DMSO (-). There was significant difference between saline+2% DMSO and the other test solutions (p<0.05). The mean absorbance values showed that the antimicrobial activity of hexane extract was slightly more effective than that of the ethanol extract and was nearly as effective as chlorhexidine (+). However, the differences in the absorbance values between the extracts of S. persica and chlorhexidine (+) were not statistically significant (p>0.05). The CFU counts of S. mutans obtained from chlorhexidine exposure were lower than from hexane and ethanol extracts. S. persica extracts were found to have antimicrobial effects on S. mutans biofilm established in vitro on orthodontic brackets suggestive of its potential use as an oral antimicrobial agent for orthodontic patients.

N-Acetyl-l-cysteine effects on multi-species oral biofilm formation and bacterial ecology

Future therapies for the treatment of dental decay have to consider the importance of preserving bacterial ecology while reducing biofilm adherence to teeth. A multi-species plaque-derived (MSPD) biofilm model was used to assess how concentrations of N-acetyl-l-cysteine (NAC) (0, 0·1, 1, 10%) affected the growth of complex oral biofilms. Biofilms were grown (n=96) for 24h on hydroxyapatite discs in BMM media with 0·5% sucrose. Bacterial viability and biomass formation was examined on each disc using a microtitre plate reader. In addition, fluorescence microscopy and Scanning Electron Microscopy was used to qualitatively examine the effect of NAC on bacterial biofilm aggregation, extracellular components and bacterial morphology. The total biomass was significantly decreased after exposure of both 1% (from 0·48, with a 95% confidence interval of (0·44, 0·57) to 0·35, with confidence interval (0·31, 0·38)) and 10% NAC (0·14 with confidence interval (0·11, 0·17)). 16S rRNA amplicon sequencing analysis indicated that 1% NAC reduced biofilm adherence while preserving biofilm ecology. As a compound with a wide safety margin, N-acetyl-l-cysteine (NAC) has the potential to be used as a long term anti-plaque bacteriostatic agent for managing chronic dental decay without substantially altering biofilm's bacterial ecology. The potential anti-caries benefit of NAC is directly related to reducing the biofilm coverage which reduces the degree of acid generation and the amount of time that the surface is exposed to a lower pH.

Urease and Dental Plaque Microbial Profiles in Children.

ObjectiveUrease enzymes produced by oral bacteria generate ammonia, which can have a significant impact on the oral ecology and, consequently, on oral health. To evaluate the relationship of urease with dental plaque microbial profiles in children as it relates to dental caries, and to identify the main contributors to this activity.Methods82 supragingival plaque samples were collected from 44 children at baseline and one year later, as part of a longitudinal study on urease and caries in children. DNA was extracted; the V3–V5 region of the 16S rRNA gene was amplified and sequenced using 454 pyrosequencing. Urease activity was measured using a spectrophotometric assay. Data were analyzed with Qiime.ResultsPlaque urease activity was significantly associated with the composition of the microbial communities of the dental plaque (Baseline P = 0.027, One Year P = 0.012). The bacterial taxa whose proportion in dental plaque exhibited significant variation by plaque urease levels in both visits were the family Pasteurellaceae (Baseline P<0.001; One Year P = 0.0148), especially Haemophilus parainfluenzae. No association was observed between these bacteria and dental caries. Bacteria in the genus Leptotrichia were negatively associated with urease and positively associated with dental caries (Bonferroni P<0.001).ConclusionsAlkali production by urease enzymes primarily from species in the family Pasteurellaceae can be an important ecological determinant in children’s dental plaque. Further studies are needed to establish the role of urease-associated bacteria in the acid/base homeostasis of the dental plaque, and in the development and prediction of dental caries in children.

Exploring the variation of oral microbiota in supragingival plaque during and after head-and-neck radiotherapy using pyrosequencing

ObjectiveThe aim of this article was to study the variation in oral microflora of the subgingival plaque during and after radiotherapy. DesignDuring and after radiotherapy, microbial samples were collected at seven time points (early stage, medium stage, and later stage of radiotherapy, and 1 month, 3 months, 6 months, and 1 year after radiotherapy) in three subjects for a total of 21 samples. Polymerase chain reaction (PCR) amplification was carried out on the 16S rDNA hypervariable V1–V3 region, and then the PCR products were determined by high-throughput pyrosequencing. ResultsThe rarefaction curve indicating the richness of the microflora demonstrated that the number of operational taxonomic units (OTUs) was in decline from the early stage of radiotherapy to the time point 1 month after radiotherapy and then trended upward. The Shannon diversity index declined during radiotherapy (ranging from 4.59 to 3.73), and generally rose after radiotherapy, with the lowest value of 3.5 (1 month after radiotherapy) and highest value of 4.75 (6 months after radiotherapy). A total of 120 genera were found; five genera (Actinomyces, Veillonella, Prevotella, Streptococcus, Campylobacter) were found in all subjects across all time points. ConclusionThe richness and diversity of oral ecology decreased with increased radiation dose, and it was gradually restored with time.

Microbiology of Oral Biofilm-Dependent Diseases: Have We Made Significant Progress to Understand and Treat These Diseases?

The oral microbiome plays a crucial role in the establishment and maintenance of oral health. Major disturbances in the interactions between this microbiome, the microenvironment, and the host may lead to the development of oral diseases. A large proportion of infectious diseases that affect humans are caused by organisms living in biofilms. This is also the case for oral infections such as dental caries, periodontal diseases, and endodontic and fungal infections. In this review, new concepts regarding the role of the oral biofilm in the etiopathogenesis of these diseases are presented, and a more ecological view of pathogenic communities as causative agents of oral diseases is discussed. We believe that a better understanding of oral biofilm physiology and ecology will provide insight for the development of new cost-effective diagnostic tools, as well as preventive and therapeutic strategies for the management of these infections.

Pulling teeth from history: DNA from ancient teeth can help to yield information about our ancestors' health, diet and diseases.

Molecular biology has made considerable contributions to the study of human history from the earliest days of our species, when our ancestors began to walk on the savannah, to the dawn of civilization and the more recent history of mankind. The analysis of contemporary mitochondrial DNA, for example, has told us that Homo sapiens first appeared in Africa; the sequencing of the Neanderthal genome has revealed that Homo sapiens and Homo neanderthalensis lived along each other and interbred before the latter disappeared; last year, the analysis of DNA extracted from a skeleton found under a parking lot in Leicester, UK, showed that it was the remains of King Richard III. Although the advent of next‐generation sequencing and advances in bioinformatics have boosted research using ancient DNA, a major hurdle has always been the quantity and quality of the DNA itself: DNA molecules quickly degrade over time into smaller fragments, and microbial contamination makes it challenging to identify human fragments within a sample. Intriguingly, teeth have proven to be an excellent source of high‐quality ancient DNA, yielding insights into the evolution of the human diet, disease and immunity since the onset of agriculture some 10,000 years ago. Dental calculus has been the most complete source of historical sequence data, especially for probing oral microbiome populations. At the same time, dental pulp—the connective tissue at the centre of teeth—has been an important source of information about ancient diseases. Archaeologist Keith Dobney, from the University of Aberdeen in the UK, and his colleagues first identified the potential of dental calculus as a source of information about past diets and microbial populations long before the advent of ancient DNA studies [1]. Now, almost 30 years later, Dobney is among those at the forefront of the revolution in ancient DNA analysis. “It appears that dental …

Altered oral viral ecology in association with periodontal disease.

ABSTRACTThe human oral cavity is home to a large and diverse community of viruses that have yet to be characterized in patients with periodontal disease. We recruited and sampled saliva and oral biofilm from a cohort of humans either periodontally healthy or with mild or significant periodontal disease to discern whether there are differences in viral communities that reflect their oral health status. We found communities of viruses inhabiting saliva and the subgingival and supragingival biofilms of each subject that were composed largely of bacteriophage. While there were homologous viruses common to different subjects and biogeographic sites, for most of the subjects, virome compositions were significantly associated with the oral sites from which they were derived. The largest distinctions between virome compositions were found when comparing the subgingival and supragingival biofilms to those of planktonic saliva. Differences in virome composition were significantly associated with oral health status for both subgingival and supragingival biofilm viruses but not for salivary viruses. Among the differences identified in virome compositions was a significant expansion of myoviruses in subgingival biofilm, suggesting that periodontal disease favors lytic phage. We also characterized the bacterial communities in each subject at each biogeographic site by using the V3 hypervariable segment of the 16S rRNA and did not identify distinctions between oral health and disease similar to those found in viral communities. The significantly altered ecology of viruses of oral biofilm in subjects with periodontal disease compared to that of relatively periodontally healthy ones suggests that viruses may serve as useful indicators of oral health status.

Effects of fatigue from sleep deprivation on experimental periodontitis in rats

Factors such as vascularization of the periodontium, inflammatory reactions and immune response affect the oral environment and ecology, decreasing host resistance and promoting the development of symptoms and the advancement of periodontal disease. Fatigue also influences the hypothalamic-pituitary-adrenal axis and reports relate it to systemic resistance. The aim of this study was to evaluate whether fatigue is a modifying factor for periodontal disease in rats. We divided 24 3-wk-old male Sprague-Dawley rats randomly into the following four groups: control; fatigue (deep sleep deprivation for 7 d); infection (rats inoculated with carboxymethyl cellulose containing periodontopathic bacteria); and compound (combined fatigue and infection conditions). Weight, serum corticosterone levels, serum albumin levels, interleukin-1β and tumor necrosis factor-α expression levels and distance from the cement-enamel junction to the alveolar bone crest were measured at baseline, and on the 36th (before sleep deprivation), 43rd (immediately after sleep deprivation) and 57th d (end of experiment). Immediately after sleep deprivation and at the end of the experiment, weight gain in the fatigue and compound groups was significantly lower than in controls (p < 0.05). Immediately after sleep deprivation, serum corticosterone levels were significantly higher in the fatigue and compound groups than in controls (p < 0.05). Moreover, serum albumin levels were significantly lower in the fatigue and compound groups than in controls (p < 0.05). Immediately after sleep deprivation, gene expression of interleukin-1β was significantly higher in the infection and compound groups than in controls (p < 0.05). Moreover, gene expression of tumor necrosis factor-α was significantly higher in the compound group than in controls (p < 0.05). At the end of the experiment, the distance from the cement-enamel junction to the alveolar bone crest was significantly higher in the infection and compound groups than in controls (p < 0.05). Moreover, the distance was significantly higher in the compound group than in the infection group. Fatigue worsened systemic health in rats and increased gingival inflammation and alveolar bone loss in experimental periodontitis. In conclusion, our results suggest that fatigue is a modifying factor for periodontal disease in rats.

Candida and Other Fungal Species

In the last half-decade or so, interest in the bacterial part of the human microbiome and its role in maintaining health have received considerable attention. Since 2009, over 300 publications have appeared describing the oral bacterial microbiome. Strikingly, fungi in the oral cavity have been studied exclusively in relation to pathologies. However, little to nothing is known about a role of fungi in establishing and maintaining a healthy oral ecology. In a healthy ecology, balance is maintained by the combined positive and negative influences between and among its members. Interactions between fungi and bacteria occur primarily at a physical and chemical level. Physical interactions are represented by (co-)adhesion and repulsion (exclusion), while chemical interactions include metabolic dependencies, quorum-sensing, and the production of antimicrobial agents. Information obtained from oral model systems and also from studies on the role of fungi in gastro-intestinal ecology indicates that fungi influence bacterial behavior through these different interactions. This review describes our current knowledge of the interactions between fungi and bacteria and aims to illustrate that further research is required to establish the role of fungi in maintaining a healthy oral cavity.

Inter‐bacterial correlations in subgingival biofilms: a large‐scale survey

Although the complexity of the oral ecology and the ecological differences between health and disease are well accepted, a clear view on the dynamics in relation to disease is lacking. In this study, the prevalence and abundance of 20 key oral bacteria was assessed in health and disease and more importantly a closer look was given to the inter-bacterial relationships. A blinded microbiological database was analysed in this cross-sectional, retrospective study. The database was constructed based on microbiological analyses of samples from 6308 patients, with gradations of periodontitis (healthy to periodontitis). Data concerning the abundance of 20 oral bacteria and probing pocket depth were provided. Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Eubacterium nodatum, Porphyromonas micra and Porphyromonas intermedia showed a clear increase in abundance and prevalence with increasing pocket depth. Correlation matrices illustrated that almost all microorganisms were in one way correlated to other species and most of these correlations were significant. Several beneficial bacteria showed strong correlations with other beneficial bacteria. Knowledge on bacterial correlations can pave the way for new treatment options focusing on restoring the shifted balance.