Actinobacillus actinomycetemcomitans in human periodontal disease: a cross-sectional microbiological investigation

Microbial interactions impact stress tolerance in a model oral community

Understanding the molecular mechanisms governing microbial interactions is crucial for unraveling the complexities of microbial communities and their ecological impacts. Here, we employed a two-species model system comprising the oral bacteria Aggregatibacter actinomycetemcomitans and Streptococcus gordonii to investigate how synergistic and antagonistic interactions between microbes impact their resilience to environmental change and invasion by other microbes. We used an in vitro colony biofilm model and focused on two S. gordonii-produced extracellular molecules, L-lactate and H2O2, which are known to impact fitness of this dual-species community. While the ability of A. actinomycetemcomitans to cross-feed on S. gordonii-produced L-lactate enhanced its fitness during co-culture, this function showed little impact on the ability of co-cultures to resist environmental change. In fact, the ability of A. actinomycetemcomitans to catabolize L-lactate may be detrimental in the presence of tetracycline, highlighting the complexity of interactions under antimicrobial stress. Furthermore, H2O2, known for its antimicrobial properties, had negative impacts on both species in our model system. However, H2O2 production by S. gordonii enhanced A. actinomycetemcomitans tolerance to tetracycline, suggesting a protective role under antibiotic pressure. Finally, S. gordonii significantly inhibited the bacterium Serratia marcescens from invading in vitro biofilms, but this inhibition was lost during co-culture with A. actinomycetemcomitans and in a murine abscess model, where S. gordonii actually promoted S. marcescens invasion. These data indicate that microbial interactions can impact fitness of a bacterial community upon exposure to stresses, but these impacts are highly environment dependent.

IMPORTANCE

Microbial interactions are critical modulators of the emergence of microbial communities and their functions. However, how these interactions impact the fitness of microbes in established communities upon exposure to environmental stresses is poorly understood. Here, we utilized a two-species community consisting of Aggregatibacter actinomycetemcomitans and Streptococcus gordonii to examine the impact of synergistic and antagonistic interactions on microbial resilience to environmental fluctuations and susceptibility to microbial invasion. We focused on the S. gordonii-produced extracellular molecules, L-lactate and H2O2, which have been shown to mediate interactions between these two microbes. We discovered that seemingly beneficial functions, such as A. actinomycetemcomitans cross-feeding on S. gordonii-produced L-Lactate, can paradoxically exacerbate vulnerabilities, such as susceptibility to antibiotics. Moreover, our data highlight the context-dependent nature of microbial interactions, emphasizing that a seemingly potent antimicrobial, such as H2O2, can have both synergistic and antagonistic effects on a microbial community dependent on the environment.

Real-time flow cytometry to assess qualitative and quantitative responses of oral pathobionts during exposure to antiseptics

Antiseptics are widely used in oral healthcare to prevent or treat oral diseases, such as gingivitis and periodontitis. However, the incidence of bacteria being tolerant to standard antiseptics has sharply increased over the last few years. This stresses the urgency for surveillance against tolerant organisms, as well as the discovery of novel antimicrobials. Traditionally, susceptibility to antimicrobials is assessed by broth micro-dilution or disk diffusion assays, both of which are time-consuming, labor-intensive, and provide limited information on the mode of action of the antimicrobials. The abovementioned limitations highlight the need for the development of new methods to monitor and further understand antimicrobial susceptibility. In this study, we used real-time flow cytometry, combined with membrane permeability staining, as a quick and sensitive technology to study the quantitative and qualitative responses of two oral pathobionts to different concentrations of chlorhexidine (CHX), cetylpyridinium chloride (CPC), or triclosan. Apart from the real-time monitoring of cell damage, we further applied a phenotypic fingerprinting method to differentiate between the bacterial subpopulations that arose due to treatment. We quantified the pathobiont damage rate of different antiseptics at different concentrations within 15 minutes of exposure and identified the conditions under which the bacteria were most susceptible. Moreover, we detected species-specific and treatment-specific phenotypic subpopulations. This proves that real-time flow cytometry can provide information on the susceptibility of different microorganisms in a short time frame while differentiating between antiseptics and thus could be a valuable tool in the discovery of novel antimicrobial compound, while at the same time deciphering their mode of action.

IMPORTANCE

With increasing evidence that microorganisms are becoming more tolerant to standard antimicrobials, faster and more accessible antimicrobial susceptibility testing methods are needed. However, traditional susceptibility assays are laborious and time-consuming. To overcome the abovementioned limitations, we introduce a novel approach to define antimicrobial susceptibility in a much shorter time frame with the use of real-time flow cytometry. Furthermore, phenotypic fingerprinting analysis can be applied on the data to study the way antiseptics affect the bacterial cell morphology over time and, thus, gain information on the mode of action of a certain compound.

Unravelling the Oral-Gut Axis: Interconnection Between Periodontitis and Inflammatory Bowel Disease, Current Challenges, and Future Perspective

As the opposite ends of the orodigestive tract, the oral cavity and the intestine share anatomical, microbial, and immunological ties that have bidirectional health implications. A growing body of evidence suggests an interconnection between oral pathologies and inflammatory bowel disease [IBD], implying a shift from the traditional concept of independent diseases to a complex, reciprocal cycle. This review outlines the evidence supporting an 'oral-gut' axis, marked by a higher prevalence of periodontitis and other oral conditions in IBD patients and vice versa. We present an in-depth examination of the interconnection between oral pathologies and IBD, highlighting the shared microbiological and immunological pathways, and proposing a 'multi-hit' hypothesis in the pathogenesis of periodontitis-mediated intestinal inflammation. Furthermore, the review underscores the critical need for a collaborative approach between dentists and gastroenterologists to provide holistic oral-systemic healthcare.

Aggregatibacter actinomycetemcomitans: From the Oral Cavity to the Heart Valves

Aggregatibacter actinomycetemcomitans (A. actinomycetecomitans) is a Gram-negative bacterial species that is an essential component of the oral microbiota. Due to its aggregative properties, it plays a role in the pathogenesis of human diseases. The presence of the surface proteins Fim, Briae, and microvesicles enables the bacterium to adhere to the epithelial surface and the tooth's surface. The presence of leukotoxin A (LtxA), which plays an important role in the pathogenicity of the bacterium, has been associated with both periodontitis and the etiology of rheumatoid arthritis (RA). A. actinomycetecomitans is also associated with several other systemic diseases and complications, such as endocarditis and different abscesses. In addition to leukotoxin A, A. actinomycetecomitans possesses several different virulence factors, including bacteriocins, chemotaxis inhibitory factors, cytotoxic factors, Fc-binding proteins, immunosuppressive factors, lipopolysaccharide collagenase, fibroblast inhibitory factors, antibiotic resistance determinants, adhesins, invasive factors and factors that inhibit the function of polymorphonuclear leukocytes. The ability of A. actinomycetemcomitans lipopolysaccharide to induce macrophages to secrete the interleukins IL-1, IL-1β, and tumor necrosis factor (TNF) is of considerable importance. The primary etiologic factor in the pathogenesis of periodontal disease is the oral biofilm colonized by anaerobic bacteria. Among these, A. actinomycetemcomitans occupies an important place as a facultative anaerobic bacterium. In addition, A. actinomycetemcomitans possesses many virulence factors that contribute to its potential to cause cancer. This article provides an overview of the virulence factors of A. actinomycetecomitans and its association with various systemic diseases, its oncogenic potential, and the treatment options for infections caused by A. actinomycetecomitans.

Point-of-care diagnostic devices for periodontitis - current trends and urgent need

Point of care (POC) diagnostic devices provide a method for rapid accurate identification of disease through analysis of biologically relevant substances. This review focuses on the utility of POC testing for early detection of periodontitis, a critical factor in treating the disease. Accessing the oral cavity for biological sampling is less invasive when compared to other internal test sites, and oral fluids contain biomarkers indicative of periodontitis. The ease of access makes the mouth an excellent target location for the development of POC devices. In this review, accepted standards in industry by which these devices must adhere, provided by the World Health Organization such as REASSURED and CLIA, are discussed. An overview is provided for many periodontal biomarkers currently being investigated as a means of predicting periodontal disease and its progression. POC devices currently being investigated for the identification and monitoring of periodontal disease such as paper-based and lab-on-a-chip based devices are outlined. Limitations of current POC devices on the market are provided and future directions in leveraging biomarkers as an adjunctive method for oral diagnosis along with AI-based analysis systems are discussed. Here, we present the ESSENCE sensor platform, which combines a porous non-planar electrode with enhanced shear flow to achieve unprecedented sensitivity and selectivity. The combination of the ESENCE chip with an automated platform allows us to meet the WHO's ASSURED criteria. This platform promises to be an exciting POC candidate for early detection of periodontitis.

Lipoxin A4 levels predict site-specific clinical improvements post scaling and root planing and correlate negatively with periodontal pathogens in severe periodontitis

BACKGROUND

Serving as a stop signal of inflammation, the role of lipoxin A4 (LXA4) in periodontitis remains to be clarified. This study is aimed to examine the changes in LXA4 levels in gingival crevicular fluid (GCF) after scaling and root planing (SRP) and to determine the relationship between LXA4 levels and treatment outcomes and periodontal pathogens in severe periodontitis.

METHODS

A total of 74 GCF samples were collected from 21 severe periodontitis participants at the deepest affected sites. These sites were re-sampled at 1, 3, and 6 months after SRP. Besides, GCF samples were also collected from 25 periodontally healthy participants. Clinical parameters including probing depth (PD) and clinical attachment level (CAL) in periodontitis group were recorded. LXA4 levels and periodontal pathogens in the GCF were analyzed by ELISA and PCR, respectively. Correlations between GCF LXA4 levels and treatment effect and periodontal pathogens were assessed.

RESULTS

LXA4 levels in GCF significantly increased after SRP (p < 0.05), but remained lower than those observed in healthy individuals (p < 0.05). Sites with lower baseline LXA4 concentrations were more likely to experience greater improvements in PD at 6 months post-SRP (area under the curve [AUC] = 0.792), and the improvements were positively correlated with the increase of LXA4 at these sites post-treatment (p < 0.05). Furthermore, more elevated LXA4 levels were observed in sites that became negative for Prevotella intermedia or Tannerella forsythia after SRP.

CONCLUSION

Baseline LXA4 in GCF has the potential to predict the site-specific response of severe periodontal lesions to SRP. The increase of LXA4 levels after treatment was positively correlated with clinical improvements and negatively correlated with the presence of Prevotella intermedia or Tannerella forsythia.

Association between human herpes simplex virus and periodontitis: results from the continuous National Health and Nutrition Examination Survey 2009-2014

BACKGROUND

Periodontitis is a common chronic oral disease which seriously affects people's quality of life. Although human herpes simplex virus (HSV) is also found in periodontal lesions, the association between HSV infection and periodontitis is unclear.

METHODS

The National Health and Nutrition Examination Survey (NHANES) data for 2009-2010, 2011-2012 and 2013-2014 was combined, and the association between HSV infection and periodontitis in the general population and particular subgroups was investigated through weighted multi-logistic analyses.

RESULTS

There were 4,733 participants aged 30-50 years old with clinically assessed periodontitis concurrent with HSV infection. In general analysis, after adjusted for covariates, both HSV-1 (OR = 1.09, P < 0.001) and HSV-2 (OR = 1.06, P = 0.030) infection was significantly associated with periodontitis. In subgroup analyses, compared with patients without HSV infection, patients with HSV-1( +) & HSV-2( +) and HSV-1( +) & HSV-2(-) infection showed higher risk of periodontitis in all subgroups (OR = 1.15, OR = 1.09, P < 0.001), while patients with HSV-1(-) & HSV-2( +) infection showed higher risk of and periodontitis only in the subgroup of people aged 40-50 years (OR = 1.10, P = 0.032) and the Mexican-American subgroup (OR = 1.35, P = 0.042). When only severe periodontitis is considered, HSV infection was associated with periodontitis, no matter the patient was infected with either of the virus or both.

CONCLUSIONS

HSV-1 infection was significantly associated with periodontitis and severe periodontitis, while HSV-2 infection was associated with severe periodontitis, and periodontitis in 40-50-year-olds and Mexican-Americans.

Unraveling the Link between Periodontitis and Inflammatory Bowel Disease: Challenges and Outlook

Periodontitis and Inflammatory Bowel Disease (IBD) are chronic inflammatory conditions, characterized by microbial dysbiosis and hyper-immunoinflammatory responses. Growing evidence suggest an interconnection between periodontitis and IBD, implying a shift from the traditional concept of independent diseases to a complex, reciprocal cycle. This review outlines the evidence supporting an "Oral-Gut" axis, marked by a higher prevalence of periodontitis in IBD patients and vice versa. The specific mechanisms linking periodontitis and IBD remain to be fully elucidated, but emerging evidence points to the ectopic colonization of the gut by oral bacteria, which promote intestinal inflammation by activating host immune responses. This review presents an in-depth examination of the interconnection between periodontitis and IBD, highlighting the shared microbiological and immunological pathways, and proposing a "multi-hit" hypothesis in the pathogenesis of periodontitis-mediated intestinal inflammation. Furthermore, the review underscores the critical need for a collaborative approach between dentists and gastroenterologists to provide holistic oral-systemic healthcare.

Regulation of adhesin synthesis in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a gram-negative bacterium associated with periodontal disease and a variety of disseminated extra-oral infections. Tissue colonization is mediated by fimbriae and non-fimbriae adhesins resulting in the formation of a sessile bacterial community or biofilm, which confers enhanced resistance to antibiotics and mechanical removal. The environmental changes experienced by A. actinomycetemcomitans during infection are detected and processed by undefined signaling pathways that alter gene expression. In this study, we have characterized the promoter region of the extracellular matrix protein adhesin A (EmaA), which is an important surface adhesin in biofilm biogenesis and disease initiation using a series of deletion constructs consisting of the emaA intergenic region and a promotor-less lacZ sequence. Two regions of the promoter sequence were found to regulate gene transcription and in silico analysis indicated the presence of multiple transcriptional regulatory binding sequences. Analysis of four regulatory elements, CpxR, ArcA, OxyR, and DeoR, was undertaken in this study. Inactivation of arcA, the regulator moiety of the ArcAB two-component signaling pathway involved in redox homeostasis, resulted in a decrease in EmaA synthesis and biofilm formation. Analysis of the promoter sequences of other adhesins identified binding sequences for the same regulatory proteins, which suggests that these proteins are involved in the coordinate regulation of adhesins required for colonization and pathogenesis.

Green Alternatives as Antimicrobial Agents in Mitigating Periodontal Diseases: A Narrative Review

Periodontal diseases and dental caries are the most common infectious oral diseases impacting oral health globally. Oral cavity health is crucial for enhancing life quality since it serves as the entranceway to general health. The oral microbiome and oral infectious diseases are strongly correlated. Gram-negative anaerobic bacteria have been associated with periodontal diseases. Due to the shortcomings of several antimicrobial medications frequently applied in dentistry, the lack of resources in developing countries, the prevalence of oral inflammatory conditions, and the rise in bacterial antibiotic resistance, there is a need for reliable, efficient, and affordable alternative solutions for the prevention and treatment of periodontal diseases. Several accessible chemical agents can alter the oral microbiota, although these substances also have unfavorable symptoms such as vomiting, diarrhea, and tooth discoloration. Natural phytochemicals generated from plants that have historically been used as medicines are categorized as prospective alternatives due to the ongoing quest for substitute products. This review concentrated on phytochemicals or herbal extracts that impact periodontal diseases by decreasing the formation of dental biofilms and plaques, preventing the proliferation of oral pathogens, and inhibiting bacterial adhesion to surfaces. Investigations examining the effectiveness and safety of plant-based medicines have also been presented, including those conducted over the past decade.

Complete Genome Sequence of Aggregatibacter actinomycetemcomitans Strain CU1000N

Here, we report the complete genome sequence of Aggregatibacter actinomycetemcomitans strain CU1000N. This rough strain is used extensively as a model organism to characterize localized aggressive periodontitis pathogenesis, the basic biology and oral cavity colonization of A. actinomycetemcomitans, and its interactions with other members of the oral microbiome.

Periodontal Disease: The Good, The Bad, and The Unknown

Periodontal disease is classically characterized by progressive destruction of the soft and hard tissues of the periodontal complex, mediated by an interplay between dysbiotic microbial communities and aberrant immune responses within gingival and periodontal tissues. Putative periodontal pathogens are enriched as the resident oral microbiota becomes dysbiotic and inflammatory responses evoke tissue destruction, thus inducing an unremitting positive feedback loop of proteolysis, inflammation, and enrichment for periodontal pathogens. Keystone microbial pathogens and sustained gingival inflammation are critical to periodontal disease progression. However, recent studies have revealed the importance of previously unidentified microbes involved in disease progression, including various viruses, phages and bacterial species. Moreover, newly identified immunological and genetic mechanisms, as well as environmental host factors, including diet and lifestyle, have been discerned in recent years as further contributory factors in periodontitis. These factors have collectively expanded the established narrative of periodontal disease progression. In line with this, new ideologies related to maintaining periodontal health and treating existing disease have been explored, such as the application of oral probiotics, to limit and attenuate disease progression. The role of systemic host pathologies, such as autoimmune disorders and diabetes, in periodontal disease pathogenesis has been well noted. Recent studies have additionally identified the reciprocated importance of periodontal disease in potentiating systemic disease states at distal sites, such as in Alzheimer's disease, inflammatory bowel diseases, and oral cancer, further highlighting the importance of the oral cavity in systemic health. Here we review long-standing knowledge of periodontal disease progression while integrating novel research concepts that have broadened our understanding of periodontal health and disease. Further, we delve into innovative hypotheses that may evolve to address significant gaps in the foundational knowledge of periodontal disease.

Adaptation by Ancient Horizontal Acquisition of Butyrate Metabolism Genes in Aggregatibacter actinomycetemcomitans

There has been considerable interest in the impact of short-chain fatty acids (SCFAs) on inflammatory effects related to the microbiome. Here, we present evidence that SCFAs may also be important in disease by providing an energy source or disease-associated cue for colonizing pathogens.

Like the bacterial residents of the human gut, it is likely that many of the species in the human oral microbiota have evolved to better occupy and persist in their niche. Aggregatibacter actinomycetemcomitans (Aa) is both a common colonizer of the oral cavity and has been implicated in the pathogenesis of periodontal disease. Here, we present a whole-genome phylogenetic analysis of Aa isolates from humans and nonhuman primates that revealed an ancient origin for this species and a long history of association with the Catarrhini, the lineage that includes Old World monkeys (OWM) and humans. Further genomic analysis showed a strong association with the presence of a short-chain fatty acid (SCFA) catabolism locus (atoRDAEB) in many human isolates that was absent in almost all nonhuman OWM isolates. We show that this locus was likely acquired through horizontal gene transfer. When grown under conditions that are similar to those at the subgingival site of periodontitis (anaerobic, SCFA replete), Aa strains with atoRDAEB formed robust biofilms and showed upregulation of genes involved in virulence, colonization, and immune evasion. Both an isogenic deletion mutant and nonhuman primate isolates lacking the ato locus failed to grow in a robust biofilm under these conditions, but grew well under the carbohydrate-rich conditions similar to those found above the gumline. We propose that the acquisition of the ato locus was a key evolutionary step allowing Aa to utilize SCFAs, adapt, and modulate subgingival disease.

Oral microbiome and pregnancy: A bidirectional relationship

The oral cavity contains the second most complex microbial population within the human body, with more than 700 bacterial organisms. Recent advances in Next Generation Sequencing technology have unraveled the complexities of the oral microbiome and provided valuable insights into its role in health and disease. The human oral microbiome varies dramatically during the different stages of life, including pregnancy. The total viable microbial counts in pregnant women are known to be higher compared to non-pregnant women, especially in the first trimester of pregnancy. A balanced oral microbiome is vital for a healthy pregnancy, as perturbations in the oral microbiome composition can contribute to pregnancy complications. On the other hand, physiological changes and differences in hormonal levels during pregnancy, increase susceptibility to various oral diseases such as gingivitis and periodontitis. A growing body of evidence supports the link between the composition of the oral microbiome and adverse pregnancy outcomes such as preterm birth, preeclampsia, low birth weight among others. This review aims to summarize the dynamics of oral microbiome during pregnancy and to discuss the relationship between a dysbiotic oral microbiome and pregnancy complications.

Oral and Fecal Microbiome in Molar-Incisor Pattern Periodontitis

In order to improve our understanding on the microbial complexity associated with Grade C/molar-incisor pattern periodontitis (GC/MIP), we surveyed the oral and fecal microbiomes of GC/MIP and compared to non-affected individuals (Control). Seven Afro-descendants with GC/MIP and seven age/race/gender-matched controls were evaluated. Biofilms from supra/subgingival sites (OB) and feces were collected and submitted to 16S rRNA sequencing. Aggregatibacter actinomycetemcomitans (Aa) JP2 clone genotyping and salivary nitrite levels were determined. Supragingival biofilm of GC/MIP presented greater abundance of opportunistic bacteria. Selenomonas was increased in subgingival healthy sites of GC/MIP compared to Control. Synergistetes and Spirochaetae were more abundant whereas Actinobacteria was reduced in OB of GC/MIP compared to controls. Aa abundance was 50 times higher in periodontal sites with PD≥ 4 mm of GC/MIP than in controls. GC/MIP oral microbiome was characterized by a reduction in commensals such as Kingella, Granulicatella, Haemophilus, Bergeyella, and Streptococcus and enrichment in periodontopathogens, especially Aa and sulfate reducing Deltaproteobacteria. The oral microbiome of the Aa JP2-like+ patient was phylogenetically distant from other GC/MIP individuals. GC/MIP presented a higher abundance of sulfidogenic bacteria in the feces, such as Desulfovibrio fairfieldensis, Erysipelothrix tonsillarum, and Peptostreptococcus anaerobius than controls. These preliminary data show that the dysbiosis of the microbiome in Afro-descendants with GC/MIP was not restricted to affected sites, but was also observed in supragingival and subgingival healthy sites, as well as in the feces. The understanding on differences of the microbiome between healthy and GC/MIP patients will help in developing strategies to improve and monitor periodontal treatment.

Periodontitis: a host mediated disruption of microbial homeostasis

PURPOSE OF REVIEW

In a prolific scientific career, Dr. Robert J. Genco dedicated himself to enriching our understanding of the pathogenesis of periodontitis. During a period of time in the 1970s and 1980s, when periodontitis was considered a classic infectious disease, Bob had the foresight to investigate and characterize the immune/inflammatory response in periodontitis, particularly Juvenile Periodontitis. His leadership in this area brought to the fore our appreciation of host-microbiome interactions that many years later (2008) culminated in the realization that periodontitis is a fundamental inflammatory disease. In this review, the question of how the host regulates the inflammatory response will be addressed in the context of how more recently-discovered pathways of resolution of inflammation play a role in disease pathogenesis.

RECENT FINDINGS

The host inflammatory response to commensal organisms creates excess inflammation in susceptible individuals and likely drives the dysbiosis of the oral microbiome observed in people with Periodontitis. In periodontal health, the oral microbiome is in balance with the host response. It is the loss of this symbiotic relationship with excess inflammation and microbiome dysbiosis that characterizes progressive disease. In recent years, the role of mediators of resolution of inflammation in the loss of balance and their potential use as therapeutics to restore homeostasis has extended our knowledge of how the host drives immune responses to affect oral dysbiosis.

SUMMARY

Dr. Genco provided the foundation for our ever-emerging understanding host-microbial interactions. The discovery of inflammation resolution pathways has furthered our knowledge in periodontal homeostasis. More studies are needed to understand how the host regulates the microbiome to fulfill the ultimate goal of more efficient therapeutics for periodontitis and related inflammatory diseases.

Herpesvirus-bacteria synergistic interaction in periodontitis

The etiopathogenesis of severe periodontitis includes herpesvirus-bacteria coinfection. This article evaluates the pathogenicity of herpesviruses (cytomegalovirus and Epstein-Barr virus) and periodontopathic bacteria (Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis) and coinfection of these infectious agents in the initiation and progression of periodontitis. Cytomegalovirus and A. actinomycetemcomitans/P. gingivalis exercise synergistic pathogenicity in the development of localized ("aggressive") juvenile periodontitis. Cytomegalovirus and Epstein-Barr virus are associated with P. gingivalis in adult types of periodontitis. Periodontal herpesviruses that enter the general circulation may also contribute to disease development in various organ systems. A 2-way interaction is likely to occur between periodontal herpesviruses and periodontopathic bacteria, with herpesviruses promoting bacterial upgrowth, and bacterial factors reactivating latent herpesviruses. Bacterial-induced gingivitis may facilitate herpesvirus colonization of the periodontium, and herpesvirus infections may impede the antibacterial host defense and alter periodontal cells to predispose for bacterial adherence and invasion. Herpesvirus-bacteria synergistic interactions, are likely to comprise an important pathogenic determinant of aggressive periodontitis. However, mechanistic investigations into the molecular and cellular interaction between periodontal herpesviruses and bacteria are still scarce. Herpesvirus-bacteria coinfection studies may yield significant new discoveries of pathogenic determinants, and drug and vaccine targets to minimize or prevent periodontitis and periodontitis-related systemic diseases.

Insights into the study and origin of the citrullinome in rheumatoid arthritis

The presence of autoantibodies and autoreactive T cells to citrullinated proteins and citrullinating enzymes in patients with rheumatoid arthritis (RA), together with the accumulation of citrullinated proteins in rheumatoid joints, provides substantial evidence that dysregulated citrullination is a hallmark feature of RA. However, understanding mechanisms that dysregulate citrullination in RA has important challenges. Citrullination is a normal process in immune and non-immune cells, which is likely activated by different conditions (eg, inflammation) with no pathogenic consequences. In a complex inflammatory environment such as the RA joint, unique strategies are therefore required to dissect specific mechanisms involved in the abnormal production of citrullinated proteins. Here, we will review current models of citrullination in RA and discuss critical components that, in our view, are relevant to understanding the accumulation of citrullinated proteins in the RA joint, collectively referred to as the RA citrullinome. In particular, we will focus on potential caveats in the study of citrullination in RA and will highlight methods to precisely detect citrullinated proteins in complex biological samples, which is a confirmatory approach to mechanistically link the RA citrullinome with unique pathogenic pathways in RA.

Periodontal herpesvirus morbidity and treatment

Four billion individuals worldwide have a history of periodontitis, with the poorest people in society most affected. Periodontitis can lead to unsightly drifting of teeth and tooth loss that may interfere with the wellbeing of daily living and has also been linked to at least 57 medical diseases and disabilities. The etiology of severe periodontitis includes active herpesviruses, specific bacterial pathogens, and destructive immune responses, but herpesviruses seem to be the major pathogenic determinant. Periodontal herpesviruses that disseminate via the systemic circulation to nonoral sites may represent a major link between periodontitis and systemic diseases. Current treatment of periodontitis focuses almost exclusively on bacterial biofilm and will require revision. Periodontal therapy that targets both herpesviruses and bacterial pathogens can provide long-term clinical improvement and potentially reduces the risk of systemic diseases. Molecular diagnostic tests for periodontal pathogens may enable early microbial identification and preemptive therapy. This review details an efficient and reliable anti-infective treatment of severe periodontitis that can be carried out in minimal time with minimal cost.

Aggregatibacter Actinomycetemcomitans: Clinical Significance of a Pathobiont Subjected to Ample Changes in Classification and Nomenclature

Aggregatibacter actinomycetemcomitans is a Gram-negative bacterium that is part of the oral microbiota. The aggregative nature of this pathogen or pathobiont is crucial to its involvement in human disease. It has been cultured from non-oral infections for more than a century, while its portrayal as an aetiological agent in periodontitis has emerged more recently. A. actinomycetemcomitans is one species among a plethora of microorganisms that constitute the oral microbiota. Although A. actinomycetemcomitans encodes several putative toxins, the complex interplay with other partners of the oral microbiota and the suppression of host response may be central for inflammation and infection in the oral cavity. The aim of this review is to provide a comprehensive update on the clinical significance, classification, and characterisation of A. actinomycetemcomitans, which has exclusive or predominant host specificity for humans.

Toll-like receptor-2 and -4 responses regulate neutrophil infiltration into the junctional epithelium and significantly contribute to the composition of the oral microbiota

BACKGROUND

Oral gingival tissue, especially the junctional epithelium (JE), is constantly exposed to sub-gingival plaque. A key component of gingival health is the regulation of the number of neutrophils that migrate into the gingival crevice to counteract its harmful effects. This report investigates the contribution of innate defense receptors, Toll-like receptor (TLR)2, TLR4, and both (TLR2/4) to the maintenance of neutrophil homeostasis in the JE.

METHODS

Bacterial composition was analyzed from whole oral swabs collected from 12- to 14-week-old TLR2, TLR4, TLR2/4 double knock-out (KO) mice using a MiSeq platform targeting the V3-V4 region of the 16S ribosomal RNA gene. Mandibles were histologically examined for quantification of neutrophils in the JE and bone loss. Lastly, total bacterial load was quantitated using quantitative real-time PCR.

RESULTS

Compared with wild-type, all TLR KO mice displayed significantly increased recruitment of neutrophils (P = 0.0079) into the JE. In addition, TLR4 and TLR2/4 KO mice demonstrated a significant increase in the number of bacteria (P = 0.0022 and P = 0.0152, respectively). Lastly, comparative compositional analyses of the oral microbiome revealed that each KO strain harbored unique microbial communities that are distinct from each other but maintained similar levels of alveolar bone.

CONCLUSIONS

Neutrophil migration into healthy mouse JE does not require TLR2 or TLR4. However, a significant increase in the number of neutrophils as well as a significant change in the oral microbial composition in both TLR2 and TLR4 KO mice demonstrate that these TLRs contribute to the homeostatic relationship between bacteria and the host in healthy mice periodontal tissue.

Rheumatoid Arthritis-Associated Mechanisms of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans

Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology characterized by immune-mediated damage of synovial joints and antibodies to citrullinated antigens. Periodontal disease, a bacterial-induced inflammatory disease of the periodontium, is commonly observed in RA and has implicated periodontal pathogens as potential triggers of the disease. In particular, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans have gained interest as microbial candidates involved in RA pathogenesis by inducing the production of citrullinated antigens. Here, we will discuss the clinical and mechanistic evidence surrounding the role of these periodontal bacteria in RA pathogenesis, which highlights a key area for the treatment and preventive interventions in RA.

Dental hypofunction alters subgingival microorganisms: a pilot study

BACKGROUND

The aim of this study was to evaluate dental plaque compositions, vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF) 1-alpha levels in gingival crevicular fluid (GCF) at hypofunctional and normofunctional teeth in healthy individuals and chronic periodontitis patients.

METHODS

Sixty systemically healthy individuals were enrolled. Study groups were: group 1 hypofunctional healthy group (group 1, N.=15); group 2 hypofunctional periodontitis group (group 2, N.=15); group 3 normofunctional healthy group (group 3, N.=15); and group 4 normofunctional periodontitis group (group 4, N.=15). Clinical periodontal measurements (plaque index, gingival index and clinical attachment level) were recorded. Dental plaque and GCF samples were taken. VEGF and HIF 1-alpha levels in GCF were determined. Subgingival plaque samples were evaluated for 11 different bacterial species as, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia, Peptostreptococcus micros, Fusobacterium nucleatum, Campylobacter rectus, Eubacterium nodatum, Eikenella corrodens and Capnocytophaga species.

RESULTS

Tannerella forsythia, Peptostreptococcus micros, Eubacterium nodatum levels decreased in hypofunctional healthy and periodontitis groups (P<0.05). Porphyromonas gingivalis levels increased in hypofunctional healthy group and decreased in hypofunctional periodontitis group (P<0.05). There was also a decrease in Eikenella corrodens levels in hypofunctional periodontitis group (P<0.05). There were no difference regarding the Aggregatibacter actinomycetemcomitans, Capnocytophaga spp., Prevotella intermedia and Fusobacterium nucleatum levels among the groups (P>0.05). VEGF and HIF-1α levels in both GCF and serum samples were also similar (P>0.05).

CONCLUSIONS

Within the limits of this study, the authors found that the levels of four significant bacterial strains were decreased in both hypofunctional healthy and hypofunctional periodontitis groups compared to normofunctional equivalents. Though not evaluated in this study, this situation could be due to periodontal ligament atrophy and related physiological alterations.

Effects of Monolaurin on Oral Microbe-Host Transcriptome and Metabolome

The aim of this in vitro study was to evaluate the effects of monolaurin against Aggregatibacter actinomycetemcomitans (Aa) and determine their effects on the host transcriptome and metabolome, using an oral cell/bacteria co-culture dual-chamber model to mimic the human periodontium. For this, the Aa, was applied to cross the monolayer of epithelial keratinocytes (OBA-9) to reach the fibroblasts layer (HGF-1) in the basal chamber. The Monolaurin treatments (25 or 50 μM) were added immediately after the inoculation of the dual-chamber with Aa. After 24 h, the transcriptional factors and metabolites produced were quantified in the remaining cell layers (insert and basal chamber) and in supernatant released from the cells. The genes IL-1α, IL-6, IL-18, and TNF analyzed in HGF-1 concentrations showed a decreased expression when treated with both concentration of Monolaurin. In keratinocytes, the genes IL-6, IL-18, and TNF presented a higher expression and the expression of IL-1α decreased when treated with the two cited concentrations. The production of glycerol and pyruvic acid increased, and the 2-deoxytetronic acid NIST, 4-aminobutyric acid, pinitol and glyceric acid, presented lower concentrations because of the treatment with 25 and/or 50 μM of Monolaurin. Use of monolaurin modulated the immune response and metabolite production when administered for 24 h in a dual-chamber model inoculated with A. actinomycetemcomitans. In summary, this study indicates that monolaurin had antimicrobial activity and modulated the host immune response and metabolite production when administered for 24 h in a dual-chamber model inoculated with A. actinomycetemcomitans.

Amphiregulin-producing γδ T cells are vital for safeguarding oral barrier immune homeostasis

Loss of oral barrier homeostasis leads to the development of periodontitis, the most common chronic inflammatory condition of mankind. Therefore, it is important to better understand the immune mediators acting at this unique barrier to safeguard tissue integrity. Here we identify a vital role for γδ T cells in constraining pathological inflammation at the oral barrier, as the absence of γδ T cells resulted in enhanced pathology during periodontitis. We show that oral barrier γδ T cells produce the reparative cytokine Amphiregulin, administration of which rescued the elevated oral pathology of tcrδ^−/− mice. Collectively, we identify a pathway controlling oral immunity mediated by barrier-resident γδ T cells, highlighting that these cells are crucial guards of oral barrier immune homeostasis.

γδ T cells are enriched at barrier sites such as the gut, skin, and lung, where their roles in maintaining barrier integrity are well established. However, how these cells contribute to homeostasis at the gingiva, a key oral barrier and site of the common chronic inflammatory disease periodontitis, has not been explored. Here we demonstrate that the gingiva is policed by γδ T cells with a T cell receptor (TCR) repertoire that diversifies during development. Gingival γδ T cells accumulated rapidly after birth in response to barrier damage, and strikingly, their absence resulted in enhanced pathology in murine models of the oral inflammatory disease periodontitis. Alterations in bacterial communities could not account for the increased disease severity seen in γδ T cell-deficient mice. Instead, gingival γδ T cells produced the wound healing associated cytokine amphiregulin, administration of which rescued the elevated oral pathology of tcrδ^−/− mice. Collectively, our results identify γδ T cells as critical constituents of the immuno-surveillance network that safeguard gingival tissue homeostasis.

Robert J. Genco: Pioneer in Oral Science Advancement

Professor Robert J. Genco made extraordinary research advances in immunology, periodontology, and microbiology research, pioneering major advances in oral science. In addition to his extraordinary research advancements in oral biology, his pioneering advances in oral science leadership at the local/university, national, and international levels are recognized worldwide, as are his educational advancements. In his era, he is truly the "father" of oral science.

Drinking alcohol is associated with variation in the human oral microbiome in a large study of American adults

BACKGROUND

Dysbiosis of the oral microbiome can lead to local oral disease and potentially to cancers of the head, neck, and digestive tract. However, little is known regarding exogenous factors contributing to such microbial imbalance.

RESULTS

We examined the impact of alcohol consumption on the oral microbiome in a cross-sectional study of 1044 US adults. Bacterial 16S rRNA genes from oral wash samples were amplified, sequenced, and assigned to bacterial taxa. We tested the association of alcohol drinking level (non-drinker, moderate drinker, or heavy drinker) and type (liquor, beer, or wine) with overall microbial composition and individual taxon abundance. The diversity of oral microbiota and overall bacterial profiles differed between heavy drinkers and non-drinkers (α-diversity richness p = 0.0059 and β-diversity unweighted UniFrac p = 0.0036), and abundance of commensal order Lactobacillales tends to be decreased with higher alcohol consumption (fold changes = 0.89 and 0.94 for heavy and moderate drinkers, p trend = 0.005 [q = 0.064]). Additionally, certain genera were enriched in subjects with higher alcohol consumption, including Actinomyces, Leptotrichia, Cardiobacterium, and Neisseria; some of these genera contain oral pathogens, while Neisseria can synthesize the human carcinogen acetaldehyde from ethanol. Wine drinkers may differ from non-drinkers in microbial diversity and profiles (α-diversity richness p = 0.048 and β-diversity unweighted UniFrac p = 0.059) after controlling for drinking amount, while liquor and beer drinkers did not. All significant differences between drinkers and non-drinkers remained after exclusion of current smokers.

CONCLUSIONS

Our results, from a large human study of alcohol consumption and the oral microbiome, indicate that alcohol consumption, and heavy drinking in particular, may influence the oral microbiome composition. These findings may have implications for better understanding the potential role that oral bacteria play in alcohol-related diseases.

What is the influence of tonsillectomy on the level of periodontal pathogens on the tongue dorsum and in periodontal pockets

BACKGROUND

For periodontal treatment, the full mouth disinfection approach suggests disinfection of oral soft tissues, such as tongue and tonsils concomitant to scaling and root planning since patients might benefit from treatment of these oral niches either. Periodontopathogenes in tonsillar tissue support this hypothesis. This prospective controlled clinical study investigated the change in the oral flora of patients who underwent tonsillectomy. Pockets were tested for eleven bacterial species before and six weeks after the surgical intervention.

METHODS

Fifty generally healthy adults were included in this study. The test group consisted of 25 patients with tonsillectomy. The control group included 25 patients with otorhinolarynologic surgery without involvement of the oral cavity. Clinical parameters such as probing pocket depth, bleeding-on-probing index and plaque index were registered the evening before surgery. Also bacterial samples from the gingival sulcus and dorsum linguae were taken, and an additional sample from the removed tonsils in the test group. Six weeks after the intervention microbial samples of pockets and tongue were taken again. Data were tested for significant differences using Wilcoxon rank and Whitney-u-test.

RESULTS

No relevant intra- or intergroup differences were found for the change of the eleven investigated species.

CONCLUSION

Based on the results of the present study, tonsillectomy does not seem to have an immediate relevant effect on the bacterial flora of tongue or periodontium. This study design was approved by the ethical committee of Zurich (KEK-ZH-Nr.2013-0419).

TRIAL REGISTRATION

The trial was retrospectively registered in the German Clinical Trials Register ( DRK00014077 ) on February 20, 2018.

Insights into the Evolution of Host Association through the Isolation and Characterization of a Novel Human Periodontal Pathobiont, Desulfobulbus oralis

The human oral microbiota encompasses representatives of many bacterial lineages that have not yet been cultured. Here we describe the isolation and characterization of previously uncultured Desulfobulbus oralis, the first human-associated representative of its genus. As mammalian-associated microbes rarely have free-living close relatives, D. oralis provides opportunities to study how bacteria adapt and evolve within a host. This sulfate-reducing deltaproteobacterium has adapted to the human oral subgingival niche by curtailing its physiological repertoire, losing some biosynthetic abilities and metabolic independence, and by dramatically reducing environmental sensing and signaling capabilities. The genes that enable free-living Desulfobulbus to synthesize the potent neurotoxin methylmercury were also lost by D. oralis, a notably positive outcome of host association. However, horizontal gene acquisitions from other members of the microbiota provided novel mechanisms of interaction with the human host, including toxins like leukotoxin and hemolysins. Proteomic and transcriptomic analysis revealed that most of those factors are actively expressed, including in the subgingival environment, and some are secreted. Similar to other known oral pathobionts, D. oralis can trigger a proinflammatory response in oral epithelial cells, suggesting a direct role in the development of periodontal disease.

Animal-associated microbiota likely assembled as a result of numerous independent colonization events by free-living microbes followed by coevolution with their host and other microbes. Through specific adaptation to various body sites and physiological niches, microbes have a wide range of contributions, from beneficial to disease causing. Desulfobulbus oralis provides insights into genomic and physiological transformations associated with transition from an open environment to a host-dependent lifestyle and the emergence of pathogenicity. Through a multifaceted mechanism triggering a proinflammatory response, D. oralis is a novel periodontal pathobiont. Even though culture-independent approaches can provide insights into the potential role of the human microbiome “dark matter,” cultivation and experimental characterization remain important to studying the roles of individual organisms in health and disease.

Utilization of Variant and Fusion Proteins To Functionally Map the Aggregatibacter actinomycetemcomitans Trimeric Autotransporter Protein ApiA

The Gram-negative bacterium Aggregatibacter actinomycetemcomitans is a causative agent of localized aggressive periodontitis. Critical to its infection process is the first and essential step of attachment, which is related to the coordinated functions of surface components comprised of proteins and extracellular polysaccharides. One such protein is the outer membrane trimeric autotransporter protein ApiA, a versatile virulence factor with numerous functions, including cell binding, invasion, serum resistance, autoaggregation, and induction of cytokine release. Here we report on the use of Escherichia coli strains expressing protein variants to define the separate functions ascribed to the N terminus and those related to the C terminus. Importantly, a hybrid protein that comprised the N terminus of trimeric ApiA and the β-barrel domain of monomeric autotransporter Aae was constructed, which allowed the expression of a monomer surface-exposed domain of ApiA. Functional and phenotypic analyses demonstrated that the C terminus of ApiA forms an independent domain that is crucial for general stability and trimer formation, which appears to be associated with autoaggregation, biofilm formation, and surface expression. Importantly, the results show that the monomeric form of the N-terminal passenger domain of ApiA, while surface exposed, is sufficient for binding to buccal epithelial cells; however, it is not sufficient to allow aggregation and biofilm formation, strengthening the importance of the role of trimerization in these phenotypes.

Aggregatibacter (Actinobacillus) actimycetemcomitans leukotoxin and human periodontitis - A historic review with emphasis on JP2

Aggregatibacter (Actinobacillus) actimycetemcomitans (Aa) is a gram-negative bacterium that colonizes the human oral cavity and is causative agent for localized aggressive (juvenile) periodontitis (AgP). In the middle of 1990s, a specific JP2 clone of belonging to the cluster of serotype b strains of Aa with highly leukotoxicity (leukotoxin, LtxA) able to kill human immune cells was isolated. JP2 clone of Aa was strongly associated with in particularly in rapidly progressing forms of aggressive periodontitis. The JP2 clone of Aa is transmitted through close contacts. Therefore, AgP patients need intense monitoring of their periodontal status as the risk for developing severely progressing periodontitis lesions are relatively high. Furthermore, timely periodontal treatment, including periodontal surgery supplemented by the use of antibiotics, is warranted. More importantly, periodontal attachment loss should be prevented by early detection of the JP2 clone of Aa by microbial diagnosis testing and/or preventive means.

Detection of Aggregatibacter actinomycetemcomitans leukotoxin and fimbria-associated protein gene genotypes among periodontitis patients and healthy controls: A case-control study

BACKGROUND

Aggregatibacter actinomycetemcomitans has been reported in higher proportions in subgingival microbiota of individuals with aggressive periodontitis (AgP) compared with those with chronic periodontitis (ChP) and healthy controls. The major virulence factors are the ones that help in colonization and evasion of host's defenses. Hence, this study was aimed to assess the prevalence of A. actinomycetemcomitans 16S rRNA and its virulent genotypes (leukotoxin [lktA] and fimbria-associated protein [fap]).

MATERIALS AND METHODS

In this case- control study We performed periodontal examination and measured probing depth and clinical attachment level (CAL). Subgingival plaque samples from 200 (ChP: n = 128 and AgP: n = 72) periodontitis patients and 200 healthy controls were screened for the presence of A. actinomycetemcomitans 16S rRNA, lktA, and fap genotypes by polymerase chain reaction. The prevalence of genotypes between periodontitis patients and healthy controls was compared with Pearson's Chi-square test. P < 0.05 was considered statistically significant.

RESULTS

Mean pocket probing depth and CAL were high as compared to the healthy controls. The prevalence of A. actinomycetemcomitans in ChP (n = 128), AgP (n = 72), and healthy individuals (n = 200) was 32.0%, 61.1%, and 2.5%, respectively. A. actinomycetemcomitans lktA genotype prevalence was 71.8% among periodontitis patients, while A. actinomycetemcomitans fap genotype showed 31.8% prevalence. The prevalence of these genotypes was insignificant in healthy controls.

CONCLUSION

The high odds ratio for A. actinomycetemcomitans prevalence suggests its strong link to periodontitis. Detection of A. actinomycetemcomitans lktA + genotype may be a useful marker for AgP as its prevalence was found to be high in AgP.

Inflammasome and Oral Diseases

One of the main steps in the development of the life in the earth is multicellularity. It enables cell differentiation and the development of morphological structures within an organism and is an essential factor in how to recognize friendly cells that are part of the multicellular organism and which foreign organisms can be harmful. Recognition includes devices such as the major histocompatibility complex (MHC), and the pattern recognition receptors (PRRs). PRRs are a group of proteins expressed by cells of the innate immune system that identify two classes of products: pathogen-associated molecular patterns (PAMPs), related to microbial pathogens, and damage-associated molecular patterns (DAMPs), associated with cell components that are released during cell damage or death. All these activate the inflammasome, which is a multiprotein oligomer that includes caspase 1, PYCARD, NALP, and caspase 5 (also known as caspase 11 or ICH-3). It is responsible for activation of inflammatory processes and has been shown to induce cell pyroptosis, a programmed cell death distinct from apoptosis, and promotes the maturation of the inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18). We review whether inflammasome is related to diseases that can occur in the oral cavity. The mouth is always a possible environment for the development of pathological conditions because of the wide variety of microorganisms. Small variations in the equilibrium of the oral flora can cause disorders that could affect the organism in a systemic form. We provide data on periodontal disease, candidiasis, herpes virus, oral cancer, caries, and other oral diseases. There are very few papers that study this issue; therefore, we need more investigation and publications about inflammatory molecular processes, and more specifically, related to the inflammasome complex.

Draft Genome Sequences of Aggregatibacter actinomycetemcomitans Strains 310a and 310b

We report the draft genome sequences of Aggregatibacter actinomycetemcomitans strains 310a (310-TR) and 310b (310-OS). Strain 310a is a clinical isolate with a rough phenotype. Strain 310b is a laboratory-adapted isolate derived from the passage of 310a and displays a smooth phenotype.

Himar1 Transposon for Efficient Random Mutagenesis in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is the primary etiological agent of aggressive periodontal disease. Identification of novel virulence factors at the genome-wide level is hindered by lack of efficient genetic tools to perform mutagenesis in this organism. The Himar1 mariner transposon is known to yield a random distribution of insertions in an organism’s genome with requirement for only a TA dinucleotide target and is independent of host-specific factors. However, the utility of this system in A. actinomycetemcomitans is unknown. In this study, we found that Himar1 transposon mutagenesis occurs at a high frequency (×10^-4), and can be universally applied to wild-type A. actinomycetemcomitans strains of serotypes a, b, and c. The Himar1 transposon inserts were stably inherited in A. actinomycetemcomitans transconjugants in the absence of antibiotics. A library of 16,000 mutant colonies of A. actinomycetemcomitans was screened for reduced biofilm formation. Mutants with transposon inserts in genes encoding pilus, putative ion transporters, multidrug resistant proteins, transcription regulators and enzymes involved in the synthesis of extracellular polymeric substance, bacterial metabolism and stress response were discovered in this screen. Our results demonstrated the utility of the Himar1 mutagenesis system as a novel genetic tool for functional genomic analysis in A. actinomycetemcomitans.

Aggregatibacter actinomycetemcomitans in African Americans with Localized Aggressive Periodontitis

This study aims to investigate the prevalence of the highly leukotoxic JP2 sequence versus the minimally leukotoxic non-JP2 sequence of Aggregatibacter actinomycetemcomitans within a cohort of 180 young African Americans, with and without localized aggressive periodontitis (LAP), in north Florida. The study included patients aged 5 to 25 y: 60 LAP patients, 60 healthy siblings (HS), and 60 unrelated healthy controls (HC). Subgingival plaque was collected from LAP sites-diseased (PD ≥5 mm with bleeding on probing) and healthy (PD ≤3 mm with no bleeding on probing)-and from healthy sites of HS and HC. Plaque DNA was extracted and analyzed by polymerase chain reaction for the detection of the JP2 and non-JP2 sequences of A. actinomycetemcomitans. Overall, 90 (50%) subjects tested positive for the JP2 sequence. Fifty (83.33%) LAP subjects were carriers of the highly leukotoxic JP2 sequence, detected in 45 (75%) diseased sites and 34 (56.67%) healthy sites. Additionally, JP2 carriage was found in 16 HS (26.67%) and 24 HC (40%; P < 0.0001, among groups). The non-JP2 sequence was detected in 26 (14.44%) total subjects: 17 (28.33%) LAP patients detected in equal amounts of diseased and healthy sites (n = 11, 18.33%), 6 (10%) HS sites, and 3 (5%) HC sites (P < 0.05, among groups). The JP2 sequence was strongly associated with LAP-diseased sites in young African Americans, significantly more so than the non-JP2 (ClinicalTrials.gov NCT01330719). Knowledge Transfer Statement: Clinicians may use the results of this study to identify susceptible individuals to aggressive periodontitis, potentially leading to more appropriate selection of therapeutic choices.

Defining Genetic Fitness Determinants and Creating Genomic Resources for an Oral Pathogen

Periodontitis is a microbial infection that destroys the structures that support the teeth. Although it is typically a chronic condition, rapidly progressing, aggressive forms are associated with the oral pathogen Aggregatibacter actinomycetemcomitans One of this bacterium's key virulence traits is its ability to attach to surfaces and form robust biofilms that resist killing by the host and antibiotics. Though much has been learned about A. actinomycetemcomitans since its initial discovery, we lack insight into a fundamental aspect of its basic biology, as we do not know the full set of genes that it requires for viability (the essential genome). Furthermore, research on A. actinomycetemcomitans is hampered by the field's lack of a mutant collection. To address these gaps, we used rapid transposon mutant sequencing (Tn-seq) to define the essential genomes of two strains of A. actinomycetemcomitans, revealing a core set of 319 genes. We then generated an arrayed mutant library comprising >1,500 unique insertions and used a sequencing-based approach to define each mutant's position (well and plate) in the library. To demonstrate its utility, we screened the library for mutants with weakened resistance to subinhibitory erythromycin, revealing the multidrug efflux pump AcrAB as a critical resistance factor. During the screen, we discovered that erythromycin induces A. actinomycetemcomitans to form biofilms. We therefore devised a novel Tn-seq-based screen to identify specific factors that mediate this phenotype and in follow-up experiments confirmed 4 mutants. Together, these studies present new insights and resources for investigating the basic biology and disease mechanisms of a human pathogen.IMPORTANCE Millions suffer from gum disease, which often is caused by Aggregatibacter actinomycetemcomitans, a bacterium that forms antibiotic-resistant biofilms. To fully understand any organism, we should be able to answer: what genes does it require for life? Here, we address this question for A. actinomycetemcomitans by determining the genes in its genome that cannot be mutated. As for the genes that can be mutated, we archived these mutants into a library, which we used to find genes that contribute to antibiotic resistance, leading us to discover that antibiotics cause A. actinomycetemcomitans to form biofilms. We then devised an approach to find genes that mediate this process and confirmed 4 genes. These results illuminate new fundamental traits of a human pathogen.

The in vivo T helper type 17 and regulatory T cell immune responses to Aggregatibacter actinomycetemcomitans

The periodontal pathogen Aggregatibacter actinomycetemcomitans is known to elicit a systemic immune response in the infected host, and occasionally causes non-oral infections. Detailed information on its immunopathological responses and the involvement of bacterial virulence factors remains to be elucidated. The aim of this study was to assess the systemic immune response to A. actinomycetemcomitans oral infection. We used an animal model that simulates systemic dissemination of the bacteria by injecting live wild-type (WT) D7S-1 and a double knockout mutant of leukotoxin and cytolethal distending toxin (ΔltxΔcdt) A. actinomycetemcomitans strains in rat oral mucosa. Draining lymph nodes were examined for regulatory T (Treg) and T helper type 17 (Th17) cell subsets and their associated mediators. An increase in the proportion of Th17 cells and a decrease in Treg cells over the experimental period of 3 weeks were similarly observed for rats challenged with WT and ΔltxΔcdt. Significant upregulation and downregulation of proinflammatory cytokines in the Th17 gene pathway was noted, as well as several qualitative differences between WT and ΔltxΔcdt. Furthermore, we observed differential fold regulation in key genes associated with a proinflammatory response in ΔltxΔcdt-inoculated rats relative to D7S-1 group. This suggests that although the knockout of these two virulence factors (ΔltxΔcdt) may suppress certain proinflammatory genes, it causes similar over-expression of other genes compared with D7S-1, indicating a common factor that still remains in the pathogenicity of A. actinomycetemcomitans.

Natural Killer Cells in the Orchestration of Chronic Inflammatory Diseases

Inflammation, altered immune cell phenotype, and functions are key features shared by diverse chronic diseases, including cardiovascular, neurodegenerative diseases, diabetes, metabolic syndrome, and cancer. Natural killer cells are innate lymphoid cells primarily involved in the immune system response to non-self-components but their plasticity is largely influenced by the pathological microenvironment. Altered NK phenotype and function have been reported in several pathological conditions, basically related to impaired or enhanced toxicity. Here we reviewed and discussed the role of NKs in selected, different, and “distant” chronic diseases, cancer, diabetes, periodontitis, and atherosclerosis, placing NK cells as crucial orchestrator of these pathologic conditions.

Periodontal Application of Manuka Honey: Antimicrobial and Demineralising Effects In Vitro

Background. Topical application of manuka honey is effective in the treatment of burns and soft-tissue infections. The aim of this study was to assess the antibacterial activity of manuka honey against plaque-associated bacteria in vitro in order to evaluate the potential application as an adjunct to periodontal treatment. Materials and Methods. The minimum bacteriostatic and bactericidal concentrations (MIC and MBC) of manuka honey were compared to those of white clover honey against a variety of plaque-associated bacteria, at the natural and neutral pH. Dissolved calcium was measured following incubation of honeys with hydroxyapatite (HA) beads to assess their potential to demineralise oral hard tissues. Results. Both honeys inhibited most tested oral bacteria at similar MIC/MBC, but Streptococcus mutans was comparatively resistant. The honeys at pH neutral had little effect on antimicrobial activity. Incubation of HA beads in honey solutions resulted in pH-dependent calcium dissolution, and inoculation with S. mutans promoted further demineralisation by both types of honey. Conclusion. Manuka honey is antimicrobial towards representative oral bacteria. However, the relative resistance of S. mutans in association with the high concentrations of fermentable carbohydrates in honey and the direct demineralising effect at natural pH mitigate against the application of honey as an adjunct in the treatment of periodontal disease.

Oral microbe-host interactions: influence of β-glucans on gene expression of inflammatory cytokines and metabolome profile

Background

The aim of this study was to evaluate the effects of β-glucan on the expression of inflammatory mediators and metabolomic profile of oral cells [keratinocytes (OBA-9) and fibroblasts (HGF-1) in a dual-chamber model] infected by Aggregatibacter actinomycetemcomitans. The periodontopathogen was applied and allowed to cross the top layer of cells (OBA-9) to reach the bottom layer of cells (HGF-1) and induce the synthesis of immune factors and cytokines in the host cells. β-glucan (10 μg/mL or 20 μg/mL) were added, and the transcriptional factors and metabolites produced were quantified in the remaining cell layers and supernatant.

Results

The relative expression of interleukin (IL)-1-α and IL-18 genes in HGF-1 decreased with 10 μg/mL or 20 μg/mL of β-glucan, where as the expression of PTGS-2 decreased only with 10 μg/mL. The expression of IL-1-α increased with 20 μg/mL and that of IL-18 increased with 10 μg/mL in OBA-9; the expression of BCL 2, EP 300, and PTGS-2 decreased with the higher dose of β-glucan. The production of the metabolite 4-aminobutyric acid presented lower concentrations under 20 μg/mL, whereas the concentrations of 2-deoxytetronic acid NIST and oxalic acid decreased at both concentrations used. Acetophenone, benzoic acid, and pinitol presented reduced concentrations only when treated with 10 μg/mL of β-glucan.

Conclusions

Treatment with β-glucans positively modulated the immune response and production of metabolites.

Periodontal Surgery Involving Modified Widman Flap Procedure and Connective Tissue Graft for Generalized Aggressive Periodontitis: A Case Report

We report a case of generalized aggressive periodontitis (AgP) requiring periodontal treatment including flap surgery and ridge augmentation. The patient was a 39-year-old woman who presented with the chief complaint of pus discharge from tooth #36. No other obvious signs of gingival inflammation were observed. Periodontal examination revealed multiple sites with a probing depth of ≥10 mm. Radiography showed pro-nounced bone defects in the maxillary incisors and molar region. Real-time PCR was used to detect Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Tannerella forsythia in subgingival plaque; all 3 pathogens were found. Based on a clinical diagnosis of generalized AgP, periodontal therapy was initiated, which resulted in an improvement in clinical and microbiological parameters. A modified Widman flap procedure was then performed on sites with residual periodontal pockets. Next, a connective tissue graft was performed for ridge augmentation at #22, which had shown evidence of ridge resorption. Postoperative reevaluation revealed a reduction in probing depth and an improvement in marginal bone levels. Oral function was then restored using a fixed bridge prosthesis and maintenance therapy initiated. The periodontal condition has remained stable over a 2.5-year period. In the present case of AgP, surgical intervention reduced periodontal pockets and periodontal pathogens and improved the architecture of both the hard and soft tissues, allowing subsequent care of the periodontium to be performed efficiently by the patient.

Mitogen-Activated Protein Kinase 2 Signaling Shapes Macrophage Plasticity in Aggregatibacter actinomycetemcomitans-Induced Bone Loss

Aggregatibacter actinomycetemcomitans is associated with aggressive periodontal disease, which is characterized by inflammation-driven alveolar bone loss. A. actinomycetemcomitans activates the p38 mitogen-activated protein kinase (MAPK) and MAPK-activated protein kinase 2 (MK2) stress pathways in macrophages that are involved in host responses. During the inflammatory process in periodontal disease, chemokines are upregulated to promote recruitment of inflammatory cells. The objective of this study was to determine the role of MK2 signaling in chemokine regulation during A. actinomycetemcomitans pathogenesis. Utilizing a murine calvarial model, Mk2+/+ and Mk2-/- mice were treated with live A. actinomycetemcomitans bacteria at the midsagittal suture. MK2 positively regulated the following macrophage RNA: Emr1 (F4/80), Itgam (CD11b), Csf1r (M-CSF Receptor), Itgal (CD11a), Tnf, and Nos2 Additionally, RNA analysis revealed that MK2 signaling regulated chemokines CCL3 and CCL4 in murine calvarial tissue. Utilizing the chimeric murine air pouch model, MK2 signaling differentially regulated CCL3 and CCL4 in the hematopoietic and nonhematopoietic compartments. Bone resorption pits in calvaria, observed by micro-computed tomography, and osteoclast formation were decreased in Mk2-/- mice compared to Mk2+/+ mice after A. actinomycetemcomitans treatment. In conclusion, these data suggest that MK2 in macrophages contributes to regulation of chemokine signaling during A. actinomycetemcomitans-induced inflammation and bone loss.

Complete Genome Sequence of Aggregatibacter actinomycetemcomitans Strain IDH781

We report here the complete genomic sequence and methylome of Aggregatibacter actinomycetemcomitans strain IDH781. This rough strain is used extensively as a model organism to characterize localized aggressive periodontitis pathogenesis, the basic biology and oral cavity colonization of A. actinomycetemcomitans, and its interactions with other members of the oral microbiome.

Surface display of Aggregatibacter actinomycetemcomitans autotransporter Aae and dispersin B hybrid act as antibiofilm agents

Among the various proteins expressed by the periodontopathogen Aggregatibacter actinomycetemcomitans, two proteins play important roles for survival in the oral cavity. The autotransporter Aae facilitates the attachment of the pathogen to oral epithelial cells, which act as a reservoir, while the biofilm-degrading glycoside hydrolase dispersin B facilitates the movement of daughter cells from the mature biofilm to a new site. The objective of this study was to use the potential of these two proteins to control biofilms. To this end, we generated a hybrid construct between the Aae C-terminal translocating domain and dispersin B, and mobilized it into Escherichia coli Rosetta (DE3) pLysS cells. Immunofluorescence analysis of the modified E. coli cells confirmed the presence of dispersin B on the surface. Further, the membrane localization of the displayed dispersin B was confirmed with Western blot analysis. The integrity of the E. coli cells displaying the dispersin B was confirmed through FACS analysis. The hydrolytic activity of the surface-displayed dispersin B was confirmed by using 4-methylumbelliferyl-β-d-glucopyranoside as the substrate. The detachment ability of the dispersin B surface-displaying E. coli cells was shown using Staphylococcus epidermidis and Actinobacillus pleuropneumoniae biofilms in a microtiter assay. We concluded that the Aae β-domain is sufficient to translocate foreign enzymes in the native folded form and that the method of Aae-mediated translocation of surface displayed enzymes might be useful for control of biofilms.

Localized aggressive periodontitis immune response to healthy and diseased subgingival plaque

AIM

The objective of this case-control study was to compare the inflammatory response of peripheral blood from localized aggressive periodontitis (LAP) patients when stimulated with healthy or diseased plaque samples.

MATERIALS AND METHODS

Whole blood and subgingival plaque samples were collected from 13 LAP subjects, 14 siblings of LAP subjects and six periodontally healthy individuals. Whole blood was stimulated for 24 h with plaque samples generated from healthy or diseased sites. The levels of 14 cyto/chemokines were detected using multiplex technology.

RESULTS

Localized aggressive periodontitis-derived cultures displayed higher levels of G-CSF, INFγ, IL10, IL12p40, IL1β, IL-6, IL-8, MCP-1, MIP-1α, and TNFα, than control cultures regardless of stimulus used. Whole blood from healthy siblings displayed higher levels of IL-6 compared to control subjects, but lower levels than those observed in cultures from LAP participants.

CONCLUSIONS

This study suggests that although bacteria is an important factor in eliciting the hyper-inflammatory response observed in LAP patients, the predisposition of host's response to bacterial presence may play a more significant role than the components of the stimulatory plaque.

Azithromycin enhances phagocytic killing of Aggregatibacter actinomycetemcomitans Y4 by human neutrophils

BACKGROUND

Aggregatibacter actinomycetemcomitans resists killing by neutrophils and is inhibited by azithromycin (AZM) and amoxicillin (AMX). AZM actively concentrates inside host cells, whereas AMX enters by diffusion. The present study is conducted to determine whether AZM is more effective than AMX at enhancing phagocytic killing of A. actinomycetemcomitans by neutrophils.

METHODS

Killing assays were conducted in the presence of either 2 μg/mL AZM or 16 μg/mL AMX (equipotent against A. actinomycetemcomitans). Neutrophils were loaded by incubation with the appropriate antibiotic. Opsonized A. actinomycetemcomitans strain Y4 was incubated with the indicated antibiotic alone, with loaded neutrophils and antibiotic, or with control neutrophils (without antibiotic) at multiplicities of infection (MOIs) of 30 and 90 bacteria per neutrophil.

RESULTS

Neutrophil incubation with 2 μg/mL AZM yielded an intracellular concentration of 10 μg/mL. At an MOI of 30, neutrophils loaded with AZM failed to kill significantly more bacteria than control neutrophils during the 60- and 90-minute assay periods. At an MOI of 90, neutrophils loaded with AZM killed significantly more bacteria than either AZM alone or control neutrophils during 60- and 90-minute incubations (P < 0.05), and killed significantly more bacteria after 90 minutes than the sum of the killing produced by AZM alone or neutrophils alone. Neutrophils incubated with AMX under identical conditions also killed significantly more bacteria than either AMX alone or control neutrophils, but there was no evidence of synergism between AMX and neutrophils.

CONCLUSIONS

Neutrophils possess a concentrative transport system for AZM that may enhance killing of A. actinomycetemcomitans. Its effects are most pronounced when neutrophils are greatly outnumbered by bacteria.