Intraspecies interactions of Streptococcus mutans impact biofilm architecture and virulence determinants in childhood dental caries

Early childhood dental caries (ECC) is the most common chronic disease among children with a heavy disease burden among low socioeconomic populations. Streptococcus mutans is most frequently associated with initiation of ECC. Many studies report children with multiple S. mutans strains (i.e., genotypes) having greater odds of developing ECC, studies investigating intraspecies interactions in dental caries are lacking. In this study, the impact of intraspecies interactions on cariogenic and fitness traits of clinical S. mutans isolates are investigated using in-vitro and in-vivo approaches. Initially clinical S. mutans isolates of 10 children from a longitudinal epidemiological study were evaluated. S. mutans strains (G09 and G18, most prevalent) isolated from one child were used for subsequent analysis. Association analysis was used to determine if presence of multiple S. mutans genotypes within the first-year of colonization was associated with caries. Biofilm analysis was performed for single and mixed cultures to assess cariogenic traits, including biofilm biomass, intra-polysaccharide, pH, and glucan. Confocal Laser Scanning Microscopy (CLSM) and time-lapse imaging were used to evaluate spatial and temporal biofilm dynamics, respectively. A Drosophila model was used to assess colonization in-vivo. Mean biofilm pH was significantly lower in co-cultured biofilms as compared with monoculture biofilms. Doubling of S. mutans in-vitro biofilms was observed by CLSM and in-vivo colonization in Drosophila for co-cultured S. mutans. Individual strains occupied specific domains in co-culture and G09 contributed most to increased co-culture biofilm thickness and colonization in Drosophila. Biofilm formation and acid production displayed distinct signatures in time-lapsed experiments.

Caries and Periodontitis: Contesting the Conventional Wisdom on Their Aetiology

We review the literature on the oral microbiome and the role of the microbiota in the development of dental caries and periodontitis. While most research has been focused on identifying one or more specific determinants of these diseases, the results have provided limited predictive value and have not been able to explain the variation in the distribution of these diseases observed in epidemiological or clinical studies. Drawing on existing knowledge about the nature of the oral microbiota, we suggest that a stochastic model based on the Weiner process provides simple and parsimonious explanations for the pathogenesis of both caries and periodontitis, making few assumptions, and providing explanations for phenomena that have hitherto proved difficult, or have required complex arguments, to explain. These diseases occur as the result of the dental hard tissues and periodontal tissues integrating the random "noise" caused by normal metabolic activities of commensal microorganisms in the dental biofilm. The processes that result in the progression and regression of caries and periodontitis may be considered as "natural," rather than pathological, even if, when left unchecked over long periods of time, they can result in the development of pathologies. The likelihood of progression or regression can be influenced by other determinants, but these processes will nevertheless occur in the absence of such influences. The distributional characteristics of the model approximate the findings of epidemiological studies indicating that, for both caries and periodontitis, there will be few sites affected in the early period after the eruption of the permanent dentition, but in those older there is an almost linear relationship with increasing age; furthermore, the longer a site survives without being affected, the less likely that it will be affected. We discuss the clinical and public health importance of these findings.

A Comparative Study of Oral Microbiota in Infants with Complete Cleft Lip and Palate or Cleft Soft Palate

Few reports have been published on the early microbiota in infants with various types of cleft palate. We assessed the formation of the oral microbiota in infants with complete cleft lip and palate (CLP n = 30) or cleft soft palate (CSP n = 25) in the neonatal period (T1 time) and again in the gum pad stage (T2 time). Culture swabs from the tongue, palate, and/or cleft margin at T1 and T2 were taken. We analysed the prevalence of the given bacterial species (the percentage) and the proportions in which the palate and tongue were colonised by each microorganism. At T1, Streptococcus mitis (S. mitis) were the most frequently detected in subjects with CLP or CSP (63% and 60%, resp.). A significantly higher frequency of methicillin-sensitive Staphylococcus aureus (S. aureus MSSA) was observed in CLP compared to the CSP group. At T2, significantly higher percentages of S. mitis, S. aureus MSSA, Staphylococcus epidermidis, and members of the Enterobacteriaceae family were noted in CLP infants compared to the CSP. S. mitis and Streptococcus sanguinis appeared with the greatest frequency on the tongue, whereas Streptococcus salivarius was predominant on the palate. The development of the microbiota in CLP subjects was characterised by a significant increase in the prevalence of pathogenic bacteria.

Salivary microbiomes of indigenous Tsimane mothers and infants are distinct despite frequent premastication

Background

Premastication, the transfer of pre-chewed food, is a common infant and young child feeding practice among the Tsimane, forager-horticulturalists living in the Bolivian Amazon. Research conducted primarily with Western populations has shown that infants harbor distinct oral microbiota from their mothers. Premastication, which is less common in these populations, may influence the colonization and maturation of infant oral microbiota, including via transmission of oral pathogens. We collected premasticated food and saliva samples from Tsimane mothers and infants (9–24 months of age) to test for evidence of bacterial transmission in premasticated foods and overlap in maternal and infant salivary microbiota. We extracted bacterial DNA from two premasticated food samples and 12 matched salivary samples from maternal-infant pairs. DNA sequencing was performed with MiSeq (Illumina). We evaluated maternal and infant microbial composition in terms of relative abundance of specific taxa, alpha and beta diversity, and dissimilarity distances.

Results

The bacteria in saliva and premasticated food were mapped to 19 phyla and 400 genera and were dominated by Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. The oral microbial communities of Tsimane mothers and infants who frequently share premasticated food were well-separated in a non-metric multi-dimensional scaling ordination (NMDS) plot. Infant microbiotas clustered together, with weighted Unifrac distances significantly differing between mothers and infants. Infant saliva contained more Firmicutes (p < 0.01) and fewer Proteobacteria (p < 0.05) than did maternal saliva. Many genera previously associated with dental and periodontal infections, e.g. Neisseria, Gemella, Rothia, Actinomyces, Fusobacterium, and Leptotrichia, were more abundant in mothers than in infants.

Conclusions

Salivary microbiota of Tsimane infants and young children up to two years of age do not appear closely related to those of their mothers, despite frequent premastication and preliminary evidence that maternal bacteria is transmitted to premasticated foods. Infant physiology and diet may constrain colonization by maternal bacteria, including several oral pathogens.

The Oral Microbiome in Health and Its Implication in Oral and Systemic Diseases

The oral microbiome can alter the balance between health and disease, locally and systemically. Within the oral cavity, bacteria, archaea, fungi, protozoa, and viruses may all be found, each having a particular role, but strongly interacting with each other and with the host, in sickness or in health. A description on how colonization occurs and how the oral microbiome dynamically evolves throughout the host's life is given. In this chapter the authors also address oral and nonoral conditions in which oral microorganisms may play a role in the etiology and progression, presenting the up-to-date knowledge on oral dysbiosis as well as the known underlying pathophysiologic mechanisms involving oral microorganisms in each condition. In oral pathology, oral microorganisms are associated with several diseases, namely dental caries, periodontal diseases, endodontic infections, and also oral cancer. In systemic diseases, nonoral infections, adverse pregnancy outcomes, cardiovascular diseases, and diabetes are among the most prevalent pathologies linked with oral cavity microorganisms. The knowledge on how colonization occurs, how oral microbiome coevolves with the host, and how oral microorganisms interact with each other may be a key factor to understand diseases etiology and progression.

Assessment of clonality and serotypes of Streptococcus mutans among children by multilocus sequence typing

Studies using multilocus sequence typing (MLST) have demonstrated that Streptococcus mutans isolates are genetically diverse. Our laboratory previously demonstrated clonality of S. mutans using MLST but could not discount the possibility of sampling bias. In this study, the clonality of randomly selected S. mutans plaque isolates from African-American children was examined using MLST. Serotype and the presence of collagen-binding proteins (CBPs) encoded by cnm/cbm were also assessed. One-hundred S. mutans isolates were randomly selected for MLST analysis. Sequence analysis was performed and phylogenetic trees were generated using start2 and mega. Thirty-four sequence types were identified, of which 27 were unique to this population. Seventy-five per cent of the isolates clustered into 16 clonal groups. The serotypes observed were c (n = 84), e (n = 3), and k (n = 11). The prevalence of S. mutans isolates of serotype k was notably high, at 17.5%. All isolates were cnm/cbm negative. The clonality of S. mutans demonstrated in this study illustrates the importance of localized population studies and are consistent with transmission. The prevalence of serotype k, a recently proposed systemic pathogen, observed in this study, is higher than reported in most populations and is the first report of S. mutans serotype k in a United States population.

Risk factors for early colonization of mutans streptococci - a multiple logistic regression analysis in Swedish 1-year-olds

BACKGROUND

Mutans streptococci (MS) are closely related to the development of dental caries and are usually established in the oral cavity during early childhood. The aim of the study was to identify factors associated with the presence of MS in Swedish 1-year-olds.

METHODS

Parents completed a questionnaire on different caries-associated factors and an oral bacterial sample was collected from 1,050 (526 boys, 524 girls) 1-year-olds. Multiple logistic regression analyses were performed to identify risk factors for colonization with MS.

RESULTS

MS were found in 27% of the 1-year-olds with teeth. High or very high MS scores (2-3) were found in 72 (7%) of the children. MS score was correlated to the number of erupted teeth (p < 0.001). No difference due to gender was found. Multiple logistic regression analysis showed that presence of bacteria was associated with: caries in a sibling, other beverages than water between meals, and more than 8 erupted teeth. High or very high MS scores (2-3) were associated with other beverages than water between meals, and more than 8 erupted teeth.

CONCLUSIONS

Number of teeth present, diet and family aspects were factors associated with presence of MS in 1-year-olds. To develop high or very high MS scores, the number of erupted teeth and dietary habits are important.

Age-dependent changes in Porphyromonas gingivalis and Prevotella species/phylotypes in healthy gingiva and inflamed/diseased sub-gingival sites

OBJECTIVES

Early colonisation of oral surfaces by periodontal pathogens presents a significant risk factor for subsequent development of destructive disease affecting tissues that support the dentition. The aims of the present study were to establish the age-dependent relationship between sub-gingival profiles of 22 Prevotella species/phylotypes in children, adolescents and adults from an isolated Aboriginal community and, further, to use this information to identify Prevotella species that could serve as microbial risk indicators.

MATERIALS AND METHODS

DNA isolated from sub-gingival plaque samples (three healthy sites and three inflamed/diseased sites) from adults, adolescents and children was screened for Porphyromonas gingivalis load and 22 Prevotella species/phylotypes by species-specific PCR.

RESULTS

A noticeable feature in adolescents was the marked increase in colonisation by P. gingivalis across all test sites. The mean number of Prevotella species/phylotypes colonising inflamed/diseased sub-gingival sites increased with age. Progressive partitioning of selected Prevotella species/phylotypes to healthy or inflamed/diseased sites was evident. Prevalence of Prevotella intermedia, Prevotella oral clone P4PB_24 and Prevotella oris increased significantly with age in diseased sites. Similarly, significant age-dependent increase in colonisation of healthy as well as inflamed/diseased sub-gingival sites was apparent for Prevotella oralis, Prevotella multiformis, Prevotella denticola, Prevotella strain P4P_53 and Prevotella oral clone BR014.

CONCLUSION

Early colonisation of children by P. gingivalis, P. intermedia and Prevotella oral clone P4PB_24 provides indication of risk for subsequent development of periodontal disease.

CLINICAL RELEVANCE

In the present study, the complexity of Prevotella species within gingival sites is explored as a basis for evaluating contribution of Prevotella species to disease.

Learned and unlearned concepts in periodontal diagnostics: a 50-year perspective

In the past 50 years, conceptual changes in the field of periodontal diagnostics have paralleled those associated with a better scientific understanding of the full spectrum of processes that affect periodontal health and disease. Fifty years ago, concepts regarding the diagnosis of periodontal diseases followed the classical pathology paradigm. It was believed that the two basic forms of destructive periodontal disease were chronic inflammatory periodontitis and 'periodontosis'- a degenerative condition. In the subsequent 25 years it was shown that periodontosis was an infection. By 1987, major new concepts regarding the diagnosis and pathogenesis of periodontitis included: (i) all cases of untreated gingivitis do not inevitably progress to periodontitis; (ii) progression of untreated periodontitis is often episodic; (iii) some sites with untreated periodontitis do not progress; (iv) a rather small population of specific bacteria ('periodontal pathogens') appear to be the main etiologic agents of chronic inflammatory periodontitis; and (v) tissue damage in periodontitis is primarily caused by inflammatory and immunologic host responses to infecting agents. The concepts that were in place by 1987 are still largely intact in 2012. However, in the decades to come, it is likely that new information on the human microbiome will change our current concepts concerning the prevention, diagnosis and treatment of periodontal diseases.

Hygiene hypothesis and periodontitis--a possible association

Hygiene hypothesis has been proposed more than two decades back to explain an increasing prevalence of allergic diseases and atopy. It states that, a lack of early childhood exposure to infectious agents increases susceptibility to allergic diseases and atopy later in life. The evidence in relation to hygiene hypothesis is controversial and inconclusive. Moreover, its underlying mechanisms are elusive and remain to be elucidated. Periodontitis is an inflammatory disease initiated by microorganisms present in the plaque biofilm. Association between periodontitis and various systemic diseases has already been established and is currently an area of interest particularly in periodontal research. Consistent with hygiene hypothesis, some researchers believed that pathogens associated with periodontal diseases might have a protective role in the development of asthma and other allergic diseases. Very few studies attempted to explore the concept of association between periodontitis, asthma and other respiratory allergic diseases which could neither support such a protective role for periodontal diseases nor reject such an association. This suggests a need for additional research to examine the relevance of hygiene hypothesis in periodontics. The purpose of the present article is to review the plausible scientific explanations available for hygiene hypothesis, to review some studies relating periodontitis, asthma and other respiratory allergic diseases and to stress the need for further research.

Five questions about Streptococcus mutans: theoretical study of its transmission and colonisation

PURPOSE

This theoretical study aimed to identify the decisive (and controllable) factors involved in Streptococcus mutans (Sm) infection through addressing questions about (i) the time and prevalence pattern (including the raison d'etre of the discrete period for the infection or WI) of initial Sm colonisation and (ii) the infant's selection of bacterial types and their diversity, which are not yet definitely answered by empirical works.

METHOD

A model of Sm infection (within-host type) was developed. For questions (i): using the basic model, stochastic simulation was performed to reproduce longitudinal observations of the initial colonisation time. A symmetrical or right-skewed gamma distribution was assumed for the maximum colonisable area (K(max)) and transmission rate (mx). Additionally, 3 or 4 developmental modes of colonisable area [K(t)] were assigned based on the K(max) value. For (ii): by extending the basic model to the two-bacterial type model, intraspecific competition analysis focusing on the differences in mx (received by the infancy) and colonisation ability (θD) was performed.

RESULTS

The basic model simulation showed that mx and K(t) played a pivotal role in determining the individual time of initial colonisation and their variations among infants in forming its prevalence patterns (with or without WI). The competition model simulation showed that higher mx could be more advantageous in competitive colonisation than higher θD under repeated invasions. Accordingly, it played a decisive role in infant's selection of initially, persistently and transiently colonising bacterial types, and thus in their diversity.

CONCLUSIONS

(i) The mx is the primary and controllable (risk) factor that extensively affects various aspects of the Sm infection process. (ii) Also, the growing carrying capacity, i.e., K(t) is another important factor when considering how to effectively delay the onset of the colonisation. (iii) Thus, currently, the most feasible and effective control measure for the infection should be microbiological interventions in the primary host with concurrent oral hygiene and dietary control in the exposed child.

Quantification of subgingival bacterial pathogens at different stages of periodontal diseases

Anaerobic gram-negative oral bacteria such as Treponema denticola, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Campylobacter rectus, and Fusobacterium nucleatum are closely associated with periodontal diseases. We measured the relative population (bacterial levels) of these oral pathogens in subgingival tissues of patients at different stages of Korean chronic periodontal diseases. We divided the individuals into those with chronic gingivitis (G), moderate periodontitis (P1), severe periodontitis (P2), and normal individuals (N) (n = 20 for each group) and subgingival tissue samples were collected. We used real-time PCR with TaqMan probes to evaluate the change of periodontal pathogens among different stages of periodontitis. Bacterial levels of A. actinomycetemcomitans and C. rectus are significantly increased in individuals with chronic gingivitis and moderate periodontitis, but unchanged in severe periodontitis patients. These results suggest that analyzing certain bacterial levels among total oral pathogens may facilitate understanding of the role of periodontal bacteria in the early stages of periodontitis.

Bacterial-killing effect of atmospheric pressure non-equilibrium plasma jet and oral mucosa response

Recently, plasma sterilization has attracted increasing attention in dental community for the atmospheric pressure non-equilibrium plasma jet (APNPs), which is driven by a kilohertz pulsed DC power, may be applied to the dental and oral diseases. However, it is still in doubt whether APNPs can effectively kill pathogenic bacteria in the oral cavity and produce no harmful effects on normal oral tissues, especially on normal mucosa. The aim of this study was to evaluate the bacterial-killing effect of APNPs in the biofilms containing a single breed of bacteria (Porphyromonas gingivalis, P.g.), and the pathological changes of the oral mucosa after treatment by APNPs. P.g. was incubated to form the biofilms in vitro, and the samples were divided into three groups randomly: group A (blank control); group B in which the biofilms were treated by APNPs (the setting of the equipment: 10 kHz, 1600 ns and 8 kV); group C in which the biofilms were exposed only to a gas jet without ignition of the plasma. Each group had three samples and each sample was processed for up to 5 min. The biofilms were then fluorescently stained, observed and photographed under a laser scanning confocal microscope. In the animal experiment, six male Japanese white rabbits were divided into two groups randomly (n=3 in each group) in terms of the different post-treatment time (1-day group and 5-day group). The buccal mucosa of the left side and the mucosa of the ventral surface of the tongue were treated by APNPs for 10 min in the same way as the bacterial biofilm experiment in each rabbit, and the corresponding mucosa of the other sides served as normal control. The clinical manifestations of the oral mucosa were observed and recorded every day. The rabbits were sacrificed one or five day(s) after APNPs treatment. The oral mucosa were harvested and prepared to haematoxylin and eosin-stained sections. Clinical observation and histopathological scores were used to assess mucosal changes. The results showed the obvious P.g. biofilms were formed at 10 days, and most of the bacteria in groups A and C were alive under a laser scanning confocal microscope, but the bacteria in the group B were almost all dead. In animal experiment, no ulcers, anabrosis and oral mucositis were found in both the 1-day and 5-day groups. The average mucous membrane irritation index was -0.83 and -0.67 in the 1-day and 5-day groups, respectively, suggesting that no intense mucosal membrane irritation responses occurred. It was concluded that APNPs could effectively kill P.g. in the biofilms and did not cause any pathological changes in the normal mucosa, suggesting that the plasma jet (APNPs) may be applied to oral diseases as a novel sterilization device in the future.

Detection of periodontal pathogens in newborns and children with mixed dentition

We report the age-related prevalence of red complex periodontal pathogens, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia, along with four strains of orange complex pathogens. The bacteria present in samples isolated from tongue, cheek, and subgingival sulcus in edentulous newborns and children with mixed dentition were monitored by polymerase chain reaction (PCR). P. gingivalis was not detected in any site of any subject in the two groups tested. However, T. denticola was not only found in the 6-13 years age group, but also in edentulous newborns at a relatively high prevalence, indicating non-dentition-related colonization by T. denticola. Campylobacter rectus, Prevotella intermedia, T. forsythia, Eikenella corrodens, and Parvimonas micra were found in the oral cavity of most subjects belonging to the 6-13 years age group compared to newborns. This suggested a pronounced association between these colonizing bacteria and the presence of teeth. There was also a strong relation between T. denticola and T. forsythia for their prevalence in the subgingival sulcus of the 6-13 years age group (p < 0.0001), but not in the other sites tested, suggesting that the colonization of dentition-related T. forsythia may be associated with the increased prevalence of non-dentition-related T. denticola in the subgingival sulcus. Overall, these results suggest that dentition is a key determinant of bacterial colonization, especially orange complex bacteria and the red complex bacterium T. forsythia.

Can oral pathogens influence allergic disease?

The hygiene hypothesis contends that fewer opportunities for infections and microbial exposures have resulted in more widespread asthma and atopic disease. Consistent with that hypothesis, decreases in infectious oral diseases over the past half century have coincided with increases in the prevalence of asthma and other allergic diseases. This observation has led some researchers to speculate that exposures to oral bacteria, including pathogens associated with periodontal diseases, such as gingivitis and periodontitis, might play a protective role in the development of asthma and allergy. Colonization of the oral cavity with bacteria, including some species of periodontal pathogens, begins shortly after birth, and the detection of serum antibodies to oral pathogens in early childhood provides evidence of an early immune response to these bacteria. Current knowledge of the immune response to oral bacteria and the immunologic pathogenesis of periodontal diseases suggests biologically plausible mechanisms by which oral pathogens could influence the risk of allergic disease. However, studies investigating the association between oral pathogen exposures and allergic disease are few in number and limited by cross-sectional or case-control design, exclusion of young children, and use of surrogate measures of oral bacterial colonization. Additional studies, particularly well-designed case-control studies among very young children and prospective birth cohort studies, are needed.

Oral microbiota of children in a school-based dental clinic

OBJECTIVES

Dental caries disproportionately affects disadvantaged subjects. This study hypothesized that there were greater caries extent and higher levels of caries-associated and anaerobic subgingival bacterial species in oral samples of Hispanic and immigrant children compared with non-Hispanic and US born children.

METHODS

Children from a school-based dental clinic serving a community with a large Hispanic component were examined, and the extent of caries was recorded. Microbial samples were taken from teeth and the tongues of children. Samples were analyzed using DNA probes to 18 oral bacterial species.

RESULTS

Seventy five children were examined. Extent of caries increased with child age in immigrant, but not in US born or Hispanic children. There were no differences in the microbiota based on ethnicity or whether the child was born in US or not. There was a higher species detection frequency from teeth than tongue samples. Levels of Streptococcus mutans and other Streptococcus spp increased with caries extent. Prevotella intermedia, Tannerella forsythia and Selenomonas spp were detected at low levels in these children.

CONCLUSIONS

We conclude that, while there was a high rate of dental caries in disadvantaged school children, there were no differences in the caries-associated microbiota, including S. mutans, based on ethnicity or immigration status. Furthermore, while anaerobic subgingival, periodontal pathogens were also detected in children, there was no difference in species detection based on ethnicity or immigration status. Increased levels of streptococci, including S. mutans, however, were detected with high caries levels. This suggested that while it is beneficial to target preventive and treatment programs to disadvantaged populations, there is likely no additional benefit to focus on subgroups within a population already at high risk for dental disease.

Enterobacteriaceae and pseudomonadaceae on the dorsum of the human tongue

OBJECTIVE

The aim of this study was to correlate the presence of Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Xanthomonadaceae on the posterior dorsum of the human tongue with the presence of tongue coating, gender, age, smoking habit and denture use.

MATERIAL AND METHODS

Bacteria were isolated from the posterior tongue dorsum of 100 individuals in MacConkey agar medium and were identified by the API 20E system (Biolab-Mérieux).

RESULTS

43% of the individuals, presented the target microorganisms on the tongue dorsum, with greater prevalence among individuals between 40 and 50 years of age (p = 0.001) and non-smokers (p=0.0485).

CONCLUSIONS

A higher prevalence of Enterobacteriaceae and Pseudomonadaceae was observed on the tongue dorsum of the individuals evaluated. There was no correlation between these species and the presence and thickness of tongue coating, gender and presence of dentures.

Microbial risk markers for childhood caries in pediatricians' offices

Dental caries in pre-school children has significant public health and health disparity implications. To determine microbial risk markers for this infection, this study aimed to compare the microbiota of children with early childhood caries with that of caries-free children. Plaque samples from incisors, molars, and the tongue from 195 children attending pediatricians' offices were assayed by 74 DNA probes and by PCR to Streptococcus mutans. Caries-associated factors included visible plaque, child age, race, and snacking habits. Species were detected more frequently from tooth than tongue samples. Lactobacillus gasseri (p < 0.01), Lactobacillus fermentum, Lactobacillus vaginalis, and S. mutans with Streptococcus sobrinus (all p < 0.05) were positively associated with caries. By multifactorial analysis, the probiotic Lactobacillus acidophilus was negatively associated with caries. Prevotella nigrescens was the only species (p < 0.05) significantly associated with caries by the 'false discovery' rate. Analysis of the data suggests that selected Lactobacillus species, in addition to mutans streptococci, are risk markers for early childhood caries.

The Bifidobacterium dentium Bd1 genome sequence reflects its genetic adaptation to the human oral cavity

Bifidobacteria, one of the relatively dominant components of the human intestinal microbiota, are considered one of the key groups of beneficial intestinal bacteria (probiotic bacteria). However, in addition to health-promoting taxa, the genus Bifidobacterium also includes Bifidobacterium dentium, an opportunistic cariogenic pathogen. The genetic basis for the ability of B. dentium to survive in the oral cavity and contribute to caries development is not understood. The genome of B. dentium Bd1, a strain isolated from dental caries, was sequenced to completion to uncover a single circular 2,636,368 base pair chromosome with 2,143 predicted open reading frames. Annotation of the genome sequence revealed multiple ways in which B. dentium has adapted to the oral environment through specialized nutrient acquisition, defences against antimicrobials, and gene products that increase fitness and competitiveness within the oral niche. B. dentium Bd1 was shown to metabolize a wide variety of carbohydrates, consistent with genome-based predictions, while colonization and persistence factors implicated in tissue adhesion, acid tolerance, and the metabolism of human saliva-derived compounds were also identified. Global transcriptome analysis demonstrated that many of the genes encoding these predicted traits are highly expressed under relevant physiological conditions. This is the first report to identify, through various genomic approaches, specific genetic adaptations of a Bifidobacterium taxon, Bifidobacterium dentium Bd1, to a lifestyle as a cariogenic microorganism in the oral cavity. In silico analysis and comparative genomic hybridization experiments clearly reveal a high level of genome conservation among various B. dentium strains. The data indicate that the genome of this opportunistic cariogen has evolved through a very limited number of horizontal gene acquisition events, highlighting the narrow boundaries that separate commensals from opportunistic pathogens.

Distribution of periodontopathic bacterial species in Japanese children with developmental disabilities

Background

Recent developments in molecular biological techniques have enabled rapid detection of periodontopathic bacterial species in clinical specimens. Accumulated evidence suggests that detection of specific bacterial species enables identification of subjects at high risk for the onset of periodontitis. We investigated the distribution of 10 selected periodontopathic bacterial species in dental plaque specimens obtained from children with disabilities who were attending daycare centers.

Methods

A total of 187 children (136 boys, 51 girls) aged 1-6 years old and diagnosed with such disabilities as mental retardation, cerebral palsy, and autism, participated in the study. Subgingival dental plaque specimens were collected from the buccal side of the maxillary left second primary molar after a clinical examination. Bacterial DNA was extracted from the specimens and PCR analyses were carried out to detect 10 selected periodontopathic species using specific primers for each. In addition, statistical analyses were performed to analyze the correlations among clinical parameters and the detected species.

Results

The most frequently detected species was Capnocytophaga sputigena (28.3%), followed by Aggregatibacter actinomycetemcomitans (20.9%) and Campylobacter rectus (18.2%). Eikenella corrodens, Capnocytophaga ochracea, and Prevotella nigrescence were detected in approximately 10% of the specimens, whereas Treponema denticola, Tannerella forsythia, and Prevotella intermedia were rarely found, and Porphyromonas gingivalis was not detected in any of the subjects. The total numbers of detected species were positively correlated with the age of the subjects. There were 10 subjects with positive reactions for T. denticola and/or T. forsythia, in whom the total number of bacterial species was significantly higher as compared to the other subjects. Furthermore, subjects possessing C. rectus showed significantly greater values for periodontal pocket depth, gingival index, and total number of species.

Conclusion

We found that approximately one-fourth of the present subjects with disabilities who possessed at least one of T. denticola, T. forsythia, and C. rectus were at possible risk for periodontitis. Follow-up examinations as well as preventive approaches should be utilized for such individuals.

Prospects for the development of probiotics and prebiotics for oral applications

There has been a paradigm shift towards an ecological and microbial community-based approach to understanding oral diseases. This has significant implications for approaches to therapy and has raised the possibility of developing novel strategies through manipulation of the resident oral microbiota and modulation of host immune responses. The increased popularity of using probiotic bacteria and/or prebiotic supplements to improve gastrointestinal health has prompted interest in the utility of this approach for oral applications. Evidence now suggests that probiotics may function not only by direct inhibition of, or enhanced competition with, pathogenic micro-organisms, but also by more subtle mechanisms including modulation of the mucosal immune system. Similarly, prebiotics could promote the growth of beneficial micro-organisms that comprise part of the resident microbiota. The evidence for the use of pro or prebiotics for the prevention of caries or periodontal diseases is reviewed, and issues that could arise from their use, as well as questions that still need to be answered, are raised. A complete understanding of the broad ecological changes induced in the mouth by probiotics or prebiotics will be essential to assess their long-term consequences for oral health and disease.

Case definition, aetiology and risk assessment of early childhood caries (ECC): a revisited review

AIM

To provide a review of the existing literature on early childhood caries (ECC) with particular reference on the nomenclature, case definition, epidemiology, etiology and risk assessment.

METHODS

An electronic search was used to identify and critically review papers that have been published and are pertinent to the above issues, evaluate and compile the reported evidence.

RESULTS

The term ECC has been adopted to more accurately describe dental caries that affects primary dentitions, replacing previously used terminology that associated the disease with the nursing habit. Suggested ECC case definition uses caries patterns as defining criteria, however, further refinement to include different clinical expressions of a varying severity is necessary. Significant percentages of preschool child populations are affected by ECC today, with the disease concentrating disproportionately in deprived families. Early colonization by mutans streptococci (MS) is associated with increased ECC development, with bacteria being transmitted in both vertical and horizontal ways. Dietary factors related to sugar consumption predispose to early MS colonization and establishment and increase the risk for ECC development, being part of the causal chain. Inappropriate bottle and breast-feeding behaviors also increase the risk, without showing a direct causal relationship. High risk children belong to ethnic minority groups and to low income families with poor parental behaviors and attitudes.

CONCLUSIONS

Further high-quality studies are needed to explore the role bacteria other than MS may play in caries initiation and progression, elucidate the interaction of the saliva immune defence system with a potentially defective tooth, and investigate the effect distant behavioral factors have on the causal chain that leads to ECC development.

Indigenous Microflora and Innate Immunity of the Head and Neck

The normal flora of the head and neck exists in a delicate balance within tightly regulated ecologic niches, counterbalanced by a highly efficient innate immune system of the host. Invasion by the normal oral flora is rare when mucosal defenses remain intact. An understanding of the indigenous microflora and the innate mucosal defense mechanisms is necessary for an appropriate evaluation of infections and therapies in this area.

The transmission of BANA-positive periodontal bacterial species from caregivers to children

BACKGROUND

The purpose of the authors' study was to use the N-benzoyl-DL-arginine-2-naphthy-lamide (BANA) test (BANAMet LLC, Ann Arbor, Mich.) to obtain information regarding the prevalence of an enzyme unique to certain periodontal pathogens in plaque samples of children, as well as the potential transmission of these pathogens from caregivers to children.

METHODS

The authors tested 218 subjects (3 to 10 years old) and 195 care-givers at four pediatric dentistry clinics in Taipei, Taiwan.

RESULTS

Forty-four percent of the children had at least one plaque sample that tested positive and/or weakly positive. Positive results were more frequent in the mixed dentition, as well as in children with gingivitis (P < .001). A logistic regression model showed that if the BANA test results for the care-giver were positive, the odds of the child's also having positive test results were 55 times greater (P < .001; confidence interval [CI] = 14 to 224) than those for a child whose caregiver had negative BANA test results. Other predictors were the presence of a mixed dentition (P < .001; odds ratio [OR] = 11; CI = 3.5 to 33.5) and the children's papillary bleeding scores (P < .001, OR = 3.1, CI = 2.0 to 4.7).

CONCLUSION

The BANA test results were positive for almost one-half of the children. A positive reaction was associated with gingivitis, a mixed dentition, a BANA-positive caregiver or a caregiver with a history of periodontal disease in the family.

CLINICAL IMPLICATIONS

The authors propose an anaerobic periodontal infection risk model in which children with a mixed dentition who have gingivitis and a caregiver with a history of periodontal disease would undergo the BANA test.

Streptococcus gordonii utilizes several distinct gene functions to recruit Porphyromonas gingivalis into a mixed community

Dental plaque biofilm formation proceeds through a developmental pathway initiated by the attachment of pioneer organisms, such as Streptococcus gordonii, to tooth surfaces. Through a variety of synergistic interactions, pioneer organisms facilitate the colonization of later arrivals including Porphyromonas gingivalis, a potential periodontal pathogen. We have investigated genes of S. gordonii required to support a heterotypic biofilm community with P. gingivalis. By screening a plasmid integration library of S. gordonii, genes were identified that are crucial for the accumulation of planktonic P. gingivalis cells into a multispecies biofilm. These genes were further investigated by specific mutation and complementation analyses. The biofilm-associated genes can be grouped into broad categories based on putative function as follows: (i) intercellular or intracellular signalling (cbe and spxB), (ii) cell wall integrity and maintenance of adhesive proteins (murE, msrA and atf), (iii) extracellular capsule biosynthesis (pgsA and atf), and (iv) physiology (gdhA, ccmA and ntpB). In addition, a gene for a hypothetical protein was identified. Biofilm visualization and quantification by confocal microscopy confirmed the role of these genes in the maturation of the multispecies community, including biofilm architectural development. The results suggest that S. gordonii governs the development of heterotypic oral biofilms through multiple genetic pathways.

Dental plaque as a biofilm and a microbial community - implications for health and disease

Dental plaque is a structurally- and functionally-organized biofilm. Plaque forms in an ordered way and has a diverse microbial composition that, in health, remains relatively stable over time (microbial homeostasis). The predominant species from diseased sites are different from those found in healthy sites, although the putative pathogens can often be detected in low numbers at normal sites. In dental caries, there is a shift toward community dominance by acidogenic and acid-tolerating species such as mutans streptococci and lactobacilli, although other species with relevant traits may be involved. Strategies to control caries could include inhibition of biofilm development (e.g. prevention of attachment of cariogenic bacteria, manipulation of cell signaling mechanisms, delivery of effective antimicrobials, etc.), or enhancement of the host defenses. Additionally, these more conventional approaches could be augmented by interference with the factors that enable the cariogenic bacteria to escape from the normal homeostatic mechanisms that restrict their growth in plaque and out compete the organisms associated with health. Evidence suggests that regular conditions of low pH in plaque select for mutans streptococci and lactobacilli. Therefore, the suppression of sugar catabolism and acid production by the use of metabolic inhibitors and non-fermentable artificial sweeteners in snacks, or the stimulation of saliva flow, could assist in the maintenance of homeostasis in plaque. Arguments will be presented that an appreciation of ecological principles will enable a more holistic approach to be taken in caries control.

Population studies of microbial ecology in periodontal health and disease

It has been established that the bacterial diversity in any given environment is severely underestimated when assessed by means of culture-based techniques. Yet, almost all currently available knowledge related to the periodontal microbiota in health and disease has been generated either by culture-based surveys or by methods that require prior species identification by culture. A handful of recent studies using culture-independent molecular methods providing 16S rRNA sequences for both cultivable and not yet cultivated species of human periodontal bacteria demonstrated a high bacterial diversity in the oral cavity. It has been estimated that approximately 500 species may colonize the human oral cavity, half of which have been cultivated to date. A review of the available epidemiological data on the prevalence of certain periodontal microbiota on a population level reveals considerable variation in estimates with respect to 1) sampling strategy, 2) mode of bacterial identification, and 3) race/ethnicity of the studied population. Nevertheless, specific bacterial profiles appear to confer high odds ratios for pathological periodontal conditions and/or progressive periodontal disease. However, the currently recognized periodontal pathogens are commonly recovered from periodontally healthy children, and their carrier rate in adults is substantial. Virulent clones, such as a highly leukotoxic strain of Actinobacillus actinomycetemcomitans, have been found to be closely associated with aggressive forms of periodontitis. In conclusion, while the majority of the periodontal microbiota are commensals, a subset of likely opportunistic pathogens fulfills the epidemiologic requirements needed in order to be ascribed as risk/causative factors. Given the large proportion of the periodontal microbial habitat that is currently insufficiently explored, and assuming that the hitherto uncultivated segment of the bacterial community will include similar levels of pathogenic species, the list of periodontal pathogens should be expected to expand.

Implants in Patients Treated for Generalized Aggressive and Chronic Periodontitis: A 3-Year Prospective Longitudinal Study

BACKGROUND

The aim of the present prospective longitudinal study of periodontally diseased and periodontally healthy patients was a clinical, microbiological, and radiographic comparison of teeth and implants and an assessment of the implant success rate.

METHODS

Thirty-nine partially edentulous patients provided with a total of 150 implants were enrolled in the study. Oral rehabilitation was undertaken in 15 patients treated for generalized aggressive periodontitis (GAgP), 12 patients treated for generalized chronic periodontitis (GCP), and 12 periodontally healthy patients. The examinations of the teeth and implants were carried out within the framework of a 3-month recall schedule over a 3-year period. At each session, clinical parameters for probing depth (PD), gingival recession (GR), attachment level (AL), gingival index (GI), and plaque index (PI) were recorded, and the composition of the subgingival microflora determined by dark-field microscopy. In the periodontally diseased patients, Actinobacillus actinomycetemcomitans (A.a.), Porphyromonas gingivalis (P.g.), and Prevotella intermedia (P.i.) were detected at teeth and implants by DNA analysis in the first and third years after insertion of the superstructure. Intraoral radiographs of the teeth and implants were taken at baseline, immediately after insertion of the superstructure, and then 1 and 3 years later.

RESULTS

The GI and PI at implants and teeth remained below 0.25 and 0.6, respectively, in all patient groups throughout the study period. At the implants and teeth, a slight increase in PD and a continuous attachment loss was recorded in the GAgP patients. The attachment loss was greater at the implants than at the teeth in all groups. The morphological distribution of the microorganisms revealed virtually healthy conditions in all groups. A.a. was detected in two GAgP patients, whereas P.g. and P.i. were found more frequently both in the GAgP and in the GCP patients. Radiographically detected bone loss was higher after 3 years at implants and teeth in the GAgP patients than in the other two groups. The implant success rates recorded were 100% in the periodontally healthy and GCP patients, and 95.7% in the maxilla and 100% in the mandible of the GAgP patients.

CONCLUSIONS

The results show that oral rehabilitation can be performed with implants in patients treated for generalized aggressive and chronic periodontitis. However, slight attachment loss and bone loss were registered at the implants and teeth in the patients with aggressive periodontitis.

Mutans streptococci in preschool twins

OBJECTIVE

The purpose of this study was to determine whether genetic factors influence variation in salivary levels of the mutans streptococci (MS) in preschool twins.

DESIGN

The study population consisted of 48 pairs of monozygotic (MZ) twins and 54 pairs of dizygotic (DZ) twins. Genotyping eight highly polymorphic DNA markers determined zygosity. Demographic data and antibiotic exposure as reported by mothers were obtained by a face-to-face interview. Salivary levels of MS were determined by the Stripmutanstrade mark test. Test results are reported on a scale of 0-3. Regression analysis, two sample t-tests and structural equation modeling were applied to analyse the data.

RESULTS

Only 6% of the participants ever visited a dentist (F component of the DMFS was 0 for this population). Average salivary scores for the mutans streptococci were significantly different between MZ (1.1+/-0.1) and DZ (0.8+/-0.1) twins (p=0.021). High salivary levels of MS (scores 2 and 3) were observed in 42% of MZ twins and in 26% of DZ twins. Regression analysis on the MS salivary levels revealed no significant effects of age, gender and antibiotic intake for MZ or DZ twins. The heritability of mutans streptococci colonisation in 48 pairs MZ and in 26 pairs of DZ twins was estimated to be 52%. The non-shared environment contribution was estimated to be 48%.

CONCLUSIONS

These results suggest that variation in the salivary levels of the mutans streptococci is significantly contributed by genetic factors.

The Relationship BetweenPorphyromonas gingivalisInfection and Local and Systemic Factors in Children

BACKGROUND

Porphyromonas gingivalis (P. gingivalis) is a major pathogen related to periodontitis. There are few reports on the prevalence and effect of P. gingivalis in children. The purpose of the present study was to describe in children the level of DNA-P gingivalis in subgingival plaque and the IgG serum reactivity to P. gingivalis (IgG-Pg), and examine their relationship to demographic, systemic, and oral variables.

METHODS

Thirty-four children, aged 1.83 to 13.42 years, were included in the study; 16 with no systemic disease and 18 with systemic conditions. The demographic data for caries incidence, plaque and gingival indices, probing depth, and alveolar bone height were recorded. The IgG-Pg and DNA-Pg levels were determined by enzyme-linked immunosorbent assay and DNA-DNA hybridization, respectively. The relationships between the IgG-Pg and DNA-Pg values to the demographics, oral parameters, and systemic conditions were examined.

RESULTS

IgG-Pg was evident in 53% of the children and DNA-Pg in 47%. IgG-Pg values significantly correlated positively with age, plaque index, and bone height. DNA-Pg values had statistically significant positive correlations with age. IgG-Pg and DNA-Pg values correlated with probing depth among children with systemic diseases. Neither the IgG-Pg nor the DNA-Pg values had a significant correlation to systemic conditions. Multiple regression analyses indicated that only age remained significantly related to IgG-Pg and DNA-Pg values.

CONCLUSIONS

P. gingivalis can be found in significant levels in the plaque of young children and elicits an immune reaction that increases with age and may be related to incipient signs of periodontal disease. Plaque DNA-Pg and serum IgG-Pg levels correlate significantly.

IgG antibody levels to Porphyromonas gingivalis and clinical measures in children

BACKGROUND

Periodontopathic clinical markers are poorly understood in the pediatric population. Several studies have proposed Porphyromonas gingivalis (P. gingivalis) and an antibody response to the microorganism as factors in periodontal tissue destruction in children. The objective of this study was to examine the prevalence of P. gingivalis in dental plaque and of serum immunoglobulin G (IgG) antibody levels to P. gingivalis, and their relationship to periodontal clinical measures in children.

METHODS

Thirty-one subjects, aged 20 to 163 months, participated in this study. Clinical measures examined included gingivitis, plaque, alveolar bone height, age, gender, ethnicity, medical status, caries, and IgG antibody levels to P. gingivalis. Five ml of blood was collected for serum analysis, and IgG antibody levels to P. gingivalis were determined by using enzyme-linked immunosorbent assay. Plaque samples were examined for the presence of P. gingivalis by DNA-DNA checkerboard. Data were analyzed on a person-level basis for relationships to serum IgG antibody levels to P. gingivalis and on a site-specific level for relationships to the presence of P. gingivalis in plaque.

RESULTS

A majority (77%) of the subjects were systemically healthy, non-white (74%), and did not have detectable P. gingivalis in their plaque. Fifty-two percent of the subjects had positive serum IgG antibody levels to P. gingivalis. Based on univariate linear regression, factors related to IgG antibody levels to P. gingivalis (P<0.05) included age, average gingival index (GI), average probing depth, and number of teeth with alveolar bone crest to cemento-enamel junction (ABC-CEJ) distances >2 mm. When all clinical measures were considered together, only age remained statistically significantly related to serum IgG antibody levels to P. gingivalis.

CONCLUSIONS

Age is one of the most important factors in the development of the immune response to putative microorganisms such as P. gingivalis in children. The role of IgG as a time-sensitive measure of periodontal health in children needs to be investigated further.

Characterization of maternal mutans streptococci transmission in an African American population

In the current literature database, information on microbiological attributes to caries outcomes in African American populations is limited and scattered. Few reports have discussed MS infection and transmission from African American mothers to their children. During the past few years, the research group at the University of Alabama at Birmingham and the Jefferson County Pubic Health Department have done a series of extensive studies to systematically investigate the prevalence of MS colonization, the time of initial MS infection as defined as "the window of infectivity," the source of MS transmission as defined as "the fidelity of transmission, and the chemotherapeutic management of MS transmission and caries prevention. The objective of this report was to summarize the main significant findings generated during a period of 15 years of study. One limitation of the studies outlined in this article is that the research populations were predominately African American families. The inclusion of white and other minorities would make the conclusions more generalizable to the US population as a whole. Nevertheless, the information presented in this report can serve as baseline knowledge for future studies of caries etiology in African American and other ethnic populations.