Aggregatibacter actinomycetemcomitans as an early colonizer of oral tissues: epithelium as a reservoir?

A Rose by Any Other Name: The Long Intricate History of Localized Aggressive Periodontitis

This review addresses the recent World Workshop Consensus Conference (WWCC) decision to eliminate Localized Aggressive Periodontitis (LAgP) in young adults as a distinct form of periodontitis. A "Consensus" implies widespread, if not unanimous, agreement among participants. However, a significant number of attendees were opposed to the elimination of the LAgP classification. The substantial evidence supporting a unique diagnosis for LAgP includes the (1) incisor/molar pattern of disease, (2) young age of onset, (3) rapid progression of attachment and bone loss, (4) familial aggregation across multiple generations, and (5) defined consortium of microbiological risk factors including Aggregatibacter actinomycetemcomitans. Distinctive clinical signs and symptoms of LAgP are presented, and the microbial subgingival consortia that precede the onset of signs and symptoms are described. Using Bradford-Hill guidelines to assess causation, well-defined longitudinal studies support the unique microbial consortia, including A. actinomycetemcomitans as causative for LAgP. To determine the effects of the WWCC elimination of LAgP on research, we searched three publication databases and discovered a clear decrease in the number of new publications addressing LAgP since the new WWCC classification. The negative effects of the WWCC guidelines on both diagnosis and treatment success are presented. For example, due to the localized nature of LAgP, the practice of averaging mean pocket depth reduction or attachment gain across all teeth masks major changes in disease recovery at high-risk tooth sites. Reinstating LAgP as a distinct disease entity is proposed, and an alternative or additional way of measuring treatment success is recommended based on an assessment of the extension of the time to relapse of subgingival re-infection. The consequences of the translocation of oral microbes to distant anatomical sites due to ignoring relapse frequency are also discussed. Additional questions and future directions are also presented.

From Global to Nano: A Geographical Perspective of Aggregatibacter actinomycetemcomitans

The periodontal disease pathobiont Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) may exert a range of detrimental effects on periodontal diseases in general and, more specifically, with the initiation and progression of Localized Stage III Grade C periodontitis (molar-incisor pattern). In this review of the biogeography of this pathobiont, the full range of geographical scales for A. actinomycetemcomitans, from global origins and transmission to local geographical regions, to more locally exposed probands and families, to the individual host, down to the oral cavity, and finally, to spatial interactions with other commensals and pathobionts within the plaque biofilms at the micron/nanoscale, are reviewed. Using the newest technologies in genetics, imaging, in vitro cultures, and other research disciplines, investigators may be able to gain new insights to the role of this pathobiont in the unique initial destructive patterns of Localized Stage III Grade C periodontitis. These findings may incorporate the unique features of the microbiome that are influenced by variations in the geographic environment within the entire mouth. Additional insights into the geographic distribution of molar-incisor periodontal breakdown for Localized Stage III Grade C periodontitis may derive from the spatial interactions between A. actinomycetemcomitans and other pathobionts such as Porphyromonas gingivalis, Filifactor aclocis, and commensals such as Streptococcus gordonii. In addition, while the association of A. actinomycetemcomitans in systemic diseases is limited at the present time, future studies into possible periodontal disease-systemic disease links may also find A. actinomycetemcomitans and its geographical interactions with other microbiome members to provide important clues as to implications of pathobiological communications.

Bacterial symbionts in oral niche use type VI secretion nanomachinery for fitness increase against pathobionts

Microbial ecosystems experience spatial and nutrient restrictions leading to the coevolution of cooperation and competition among cohabiting species. To increase their fitness for survival, bacteria exploit machinery to antagonizing rival species upon close contact. As such, the bacterial type VI secretion system (T6SS) nanomachinery, typically expressed by pathobionts, can transport proteins directly into eukaryotic or prokaryotic cells, consequently killing cohabiting competitors. Here, we demonstrate for the first time that oral symbiont Aggregatibacter aphrophilus possesses a T6SS and can eliminate its close relative oral pathobiont Aggregatibacter actinomycetemcomitans using its T6SS. These findings bring nearer the anti-bacterial prospects of symbionts against cohabiting pathobionts while introducing the presence of an active T6SS in the oral cavity.

Evaluation of the antibacterial activity of cinnamon essential oil and its individual compounds on Aggregatibacter actinomycetemcomitans isolated from black extrinsic tooth stain: an in vitro study

AIM

Black extrinsic tooth stain (BETS) is a health challenge that commonly affects children. Aggregatibacter actinomycetemcomitans (Aa) presents in higher prevalence within the polymicrobial community of BETS. In this study, the anti-planktonic and anti-sessile activities of cinnamon essential oil (CEO) and its individual compounds against Aa were evaluated. The preventive effect of CEO and its active substances on BETS formation was also studied in vitro.

METHODS

Aa was isolated from a preschool child with BETS and was identified based on the morphological characteristics, MALDI-TOF mass spectroscopy and 16S rRNA sequencing. The effect of CEO and its individual compounds on the growth kinetics of planktonic and sessile Aa cells as well as their antibacterial efficacy and their rate of bacterial killing were examined. The preventive effect of CEO and its active substances on the formation of BETS was evaluated using an ex vivo model. The data were analysed using one-way analysis of variance (ANOVA) and the significance level was set at p < 0.05.

RESULTS

Out of eight individual compounds of CEO, only eugenol, cinnamaldehyde and α-methyl cinnamaldehyde showed anti-Aa activities. The values of the minimum inhibitory concentrations (MICs) were in the following order: CEO (421.5 mg/ml) > α-methyl cinnamaldehyde (26.37 mg/ml) > cinnamaldehyde (0.209 mg/ml) > eugenol (0.052 mg/ml). CEO, eugenol, cinnamaldehyde and α-methyl cinnamaldehyde, respectively, exhibited two-, four-, four- and eightfold increase of sessile MIC compared to their planktonic MIC. The growth kinetics of both planktonic and sessile Aa in the presence of CEO, eugenol, cinnamaldehyde and α-methyl cinnamaldehyde revealed a complete inhibition at the MICs and 5.3%-37.4% biofilm inhibition at sub-MICs. The time-killing study demonstrated that CEO, eugenol and cinnamaldehyde were capable of reducing the survival rate of both planktonic and sessile Aa cells after 15-20 and 25-30 min, respectively. However, α-methyl cinnamaldehyde showed a superior anti-planktonic to anti-biofilm activity. The daily incorporation of CEO, eugenol and cinnamaldehyde at their MICs for 14 days totally prevented the formation of BETS in the ex vivo model; however, in the case of α-methyl cinnamaldehyde, BETS was visually detectable after 10 days.

CONCLUSION

CEO and its individual compounds have marked antibacterial activity against Aa. The effective results against planktonic and sessile Aa within reasonable time indicate that they can be used to prevent BETS.

Aggregatibacter actinomycetemcomitans cytolethal distending toxin modulates host phagocytic function

Cytolethal distending toxins (Cdt) are a family of toxins produced by several human pathogens which infect mucocutaneous tissue and induce inflammatory disease. Human macrophages exposed to Aggregatibacter actinomycetemcomitans (Aa) Cdt respond through canonical and non-canonical inflammasome activation to stimulate cytokine release. The inflammatory response is dependent on PI3K signaling blockade via the toxin's phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase activity; converting PIP3 to phosphatidylinsoitol-3,4-diphosphate (PI3,4P2) thereby depleting PIP3 pools. Phosphoinositides, also play a critical role in phagosome trafficking, serving as binding domains for effector proteins during phagosome maturation and subsequent fusion with lysosomes. We now demonstrate that AaCdt manipulates the phosphoinositide (PI) pools of phagosome membranes and alters Rab5 association. Exposure of macrophages to AaCdt slowed phagosome maturation and decreased phago-lysosome formation, thereby compromising macrophage phagocytic function. Moreover, macrophages exposed to Cdt showed decreased bactericidal capacity leading to increase in Aggregatibacter actinomycetemcomitans survival. Thus, Cdt may contribute to increased susceptibility to bacterial infection. These studies uncover an underexplored aspect of Cdt function and provide new insight into the virulence potential of Cdt in mediating the pathogenesis of disease caused by Cdt-producing organisms such as Aa.

Antibodies to oral pathobionts and colon cancer risk in the CLUE I cohort study

Periodontitis has been associated with an increased risk for gastrointestinal cancers. The objective of our study was to investigate the association of antibodies to oral bacteria and the risk of colon cancer in a cohort setting. Using the CLUE I cohort, a prospective cohort initiated in 1974 in Washington County, Maryland, we conducted a nested case-control study to examine the association of levels of IgG antibodies to 11 oral bacterial species (13 total strains) with risk of colon cancer diagnosed a median of 16 years later (range: 1-26 years). Antibody response was measured using checkerboard immunoblotting assays. We included 200 colon cancer cases and 200 controls matched on age, sex, cigarette smoking status, time of blood draw and pipe or cigar smoking status. Controls were selected using incidence density sampling. Conditional logistic regression models were used to assess the association between antibody levels and colon cancer risk. In the overall analysis, we observed significant inverse associations for 6 of the 13 antibodies measured (P-trends <.05) and one positive association for antibody levels to Aggregatibacter actinomycetemcomitans (ATCC 29523; P-trend = .04). While we cannot rule out a role for periodontal disease in colon cancer risk, findings from our study suggest that a strong adaptive immune response may be associated with a lower risk of colon cancer. More studies will need to examine whether the positive associations we observed with antibodies to A. actinomycetemcomitans reflect a true causal association for this bacterium.

Succession of oral bacterial colonizers on dental implant materials: An in vitro biofilm model

OBJECTIVES

Oral bacterial adhesion on dental implant materials has been extensively studied using in vitro systems but has yielded results restricted to in vitro growth patterns due to limitations in species selection, sustained fastidious anaerobe growth, and mixed culture longevity. The aim of this study was to develop an oral bacterial biofilm model consisting of colonizers representative of the oral microbiome exhibiting temporal shifts characteristic of plaque development and maturation in vivo.

METHODS

Streptococcus oralis, Actinomyces naeslundii, Aggregatibacter actinomycetemcomitans, Veillonella parvula, Fusobacterium nucleatum, and Porphyromonas gingivalis were grown in monoculture prior to combination in mixed culture. Commercially pure titanium (cpTi) and yttria-stabilized zirconia (ZrO2) disks with polished, acid-etched, or sandblasted surfaces were prepared to evaluate oral bacterial adhesion. After 6 h, 1, 3, 7, 14 and 21 days, genomic DNA from planktonic and adherent bacteria was isolated. Quantitative polymerase chain reaction (qPCR) was used to enumerate the amount and proportion of each species.

RESULTS

Early-colonizing S. oralis and A. actinomycetemcomitans, dominated after 6 h prior to secondary colonization by F. nucleatum and V. parvula in planktonic (1 day) and sessile (3 days) form. A. naeslundii maintained relatively low but stable bacterial counts throughout testing. After 14 days, late-colonizing P. gingivalis became established in mixed culture and persisted, becoming the dominant species after 21 days. The composition of adherent bacteria across all substrates was statistically similar at all timepoints with notable exceptions including lower S. oralis bacterial counts on polished cpTi (3 days).

SIGNIFICANCE

Within the present model's limitations, multispecies oral bacterial attachment is similar on surface-treated cpTi and ZrO2.

Interactions between probiotic and oral pathogenic strains

More than 6 billion bacteria and other microorganisms live in the adult oral cavity. As a result of any deleterious effect on this community, some microorganisms will survive better than others, which may trigger pathogenic processes like caries, halitosis, gingivitis or periodontitis. Oral dysbiosis is among the most frequent human health hazards globally. Quality of life of patients deteriorates notably, while treatments are often unpleasant, expensive and irreversible, e.g. tooth loss. In the experiments reported here, we investigated the individual interactions between 8 pathogenic and 8 probiotic strains and a commercially available probiotic product. Almost all pathogens, namely Fusobacterium nucleatum, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Streptococcus mutans, Streptococcus oralis, Streptococcus gordonii, Enterococcus faecalis and Prevotella buccae are pathogens frequently occurring in the oral cavity. The used probiotic strains were Lactobacillus plantarum, Lactobacillus rhamnosus, Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus delbrueckii, Bifidobacterium thermophilum and two Streptococcus dentisani isolates. Using a modified agar diffusion method, we investigated capability of the probiotic bacteria to prevent the growth of the pathogenic ones in order to identify candidates for future therapeutic treatments. The results indicated successful bacteriocin production, i.e. growth inhibition, against every pathogenic bacterium by at least 5 probiotic strains.

Salivary Biomarkers for Dental Caries Detection and Personalized Monitoring

This study investigated the potential of salivary bacterial and protein markers for evaluating the disease status in healthy individuals or patients with gingivitis or caries. Saliva samples from caries- and gingivitis-free individuals (n = 18), patients with gingivitis (n = 17), or patients with deep caries lesions (n = 38) were collected and analyzed for 44 candidate biomarkers (cytokines, chemokines, growth factors, matrix metalloproteinases, a metallopeptidase inhibitor, proteolytic enzymes, and selected oral bacteria). The resulting data were subjected to principal component analysis and used as a training set for random forest (RF) modeling. This computational analysis revealed four biomarkers (IL-4, IL-13, IL-2-RA, and eotaxin/CCL11) to be of high importance for the correct depiction of caries in 37 of 38 patients. The RF model was then used to classify 10 subjects (five caries-/gingivitis-free and five with caries), who were followed over a period of six months. The results were compared to the clinical assessments of dental specialists, revealing a high correlation between the RF prediction and the clinical classification. Due to the superior sensitivity of the RF model, there was a divergence in the prediction of two caries and four caries-/gingivitis-free subjects. These findings suggest IL-4, IL-13, IL-2-RA, and eotaxin/CCL11 as potential salivary biomarkers for identifying noninvasive caries. Furthermore, we suggest a potential association between JAK/STAT signaling and dental caries onset and progression.

Lactobacilli postbiotics reduce biofilm formation and alter transcription of virulence genes of Aggregatibacter actinomycetemcomitans

Periodontitis is characterized by a dysbiotic microbial community and treatment strategies include the reestablishment of symbiosis by reducing pathogens abundance. Aggregatibacter actinomycetemcomitans (Aa) is frequently associated with rapidly progressing periodontitis. Since the oral ecosystem may be affected by metabolic end-products of bacteria, we evaluated the effect of soluble compounds released by probiotic lactobacilli, known as postbiotics, on Aa biofilm and expression of virulence-associated genes. Cell-free pH-neutralized supernatants (CFS) of Lactobacillus rhamnosus Lr32, L. rhamnosus HN001, Lactobacillus acidophilus LA5, and L. acidophilus NCFM were tested against a fimbriated clinical isolate of Aa JP2 genotype (1 × 10⁷  CFU/well) on biofilm formation for 24 hr, and early and mature preformed biofilms (2 and 24 hr). Lactobacilli CFS partially reduced Aa viable counts and biofilms biomass, but did not affect the number of viable non-adherent bacteria, except for LA5 CFS. Furthermore, LA5 CFS and, in a lesser extent HN001 CFS, influenced Aa preformed biofilms. Lactobacilli postbiotics altered expression profile of Aa in a strain-specific fashion. Transcription of cytolethal distending toxin (cdtB) and leukotoxin (ltxA) was downregulated by CFS of LA5 and LR32 CFS. Although all probiotics produced detectable peroxide, transcription of katA was downregulated by lactobacilli CFS. Transcription of dspB was abrogated by LR32 and NCFM CFS, but increased by HN001, whereas expression of pgA was not affected by any postbiotic. Our data indicated the potential of postbiotics from lactobacilli, especially LA5, to reduce colonization levels of Aa and to modulate the expression of virulence factors implicated in evasion of host defenses.

Remnant oral biofilm and microorganisms after autoclaving sterilization of retrieved healing abutments

OBJECTIVE

The purpose of this study was to evaluate the sterilization effectiveness against biofilms on retrieved healing abutments used in implant dentistry.

BACKGROUND

A large number of clinicians reuse healing abutments to decrease treatment costs although it can promote infection due to the presence of remnant biofilm biomass.

METHODS

One hundred and eighty-five titanium healing abutments previously used for 3 months in oral cavity were assessed in this study. Abutments were submitted to cleaning, chemical disinfection, and autoclave sterilization according to clinical guidelines. The abutments were aseptically placed into glass tubes containing specific bacterial growth medium and then incubated for 10 days. From glass tubes with bacterial growth, 100 µl medium was transferred to Schaedler's agar for morphological identification and counting of strict anaerobes and to Columbia blood agar for presumptive identification of facultative anaerobes after incubation. Isolated strains were then identified at species level by enzymatic and biochemical tests within API microorganism detection platform. Also, polymerase chain reaction (PCR) was performed for identification of undefined strains.

RESULTS

After the standard cleaning and sterilization procedures, fifty-six (approximately 30%) retrieved abutments showed the presence of remnant biofilm biomass. The bacteria identified into the remnant biofilms covering the abutments were representative of the commensal oral microbiota including Aggregatibacter actinomycetemcomitans, Prevotella intermedia, and Enterococcus faecalis.

CONCLUSION

Although some healing abutments did not reveal the existence of bacteria, organic components from biofilm biomass are still strongly adhered on the retentive micro-regions and surfaces of abutments and therefore that would support the accumulation of biofilm including pathogenic species leading to patients' cross-infections. Further studies should be performed on the assessment of different materials, design, and connections of the healing abutments associated with clinical disinfection procedures in implant dentistry.

Aggregatibacter, A Low Abundance Pathobiont That Influences Biogeography, Microbial Dysbiosis, and Host Defense Capabilities in Periodontitis: The History of A Bug, And Localization of Disease

Aggregatibacter actinomycetemcomitans, the focus of this review, was initially proposed as a microbe directly related to a phenotypically distinct form of periodontitis called localized juvenile periodontitis. At the time, it seemed as if specific microbes were implicated as the cause of distinct forms of disease. Over the years, much has changed. The sense that specific microbes relate to distinct forms of disease has been challenged, as has the sense that distinct forms of periodontitis exist. This review consists of two components. The first part is presented as a detective story where we attempt to determine what role, if any, Aggregatibacter plays as a participant in disease. The second part describes landscape ecology in the context of how the host environment shapes the framework of local microbial dysbiosis. We then conjecture as to how the local host response may limit the damage caused by pathobionts. We propose that the host may overcome the constant barrage of a dysbiotic microbiota by confining it to a local tooth site. We conclude speculating that the host response can confine local damage by restricting bacteremic translocation of members of the oral microbiota to distant organs thus constraining morbidity and mortality of the host.

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.

Detection of periodontal pathogens in mothers of preterm birth and/or low weight

Background

The present study aims to estimate the possible relationship between periodontal pathogens in the oral cavity and the birth of Preterm Birth (PTB) and/or Low Birth Weight (LBW).

Material and Methods

It’s a case- control study with the subgengival biofilm samples were collected from four sites up deeper until 48 hours postpartum and were processes by Polymerase Chain Reaction (PCR) for presence the periodontal pathogens Prevotella intermedia (Pi), Fusobacterium nucleatum (Fn), Porphyromonas gingivalis (Pg), Treponema denticola (Td),  Tannerella forsythia (Tf) e Aggregatibacter actinomycetemcomitans (Aa). The mothers were divided into case grup (babies weighing < 2500g and/or gestational age < 37 weeks) and control group (babies weighing ≥ 2500g and gestational age ≥ 37 weeks). Chi-square test and the measure of association obtained by Odds Ratio (OR) were used to estimate the association between the variables.

Results

Microbial analyses results showed no significant association between PTB and LBW with most periodontal pathogens in the oral cavity, even with association with the clinical presence of periodontitis.

Conclusions

given the high presence of periodontal pathogens in the biofilm subgengival of recent mothers, it is suggested that the findings of this research serve as the basis for future studies on the pathophysiology involved in the relationship between periodontitis and PTB and/or LBW.

Key words:Low Birth Weight Infant. Premature Infant. Periodontal Diseases. Bacteria. Polymerase Chain Reaction.

Diversity patterns of bacteriophages infecting Aggregatibacter and Haemophilus species across clades and niches

Aggregatibacter and Haemophilus species are relevant human commensals and opportunistic pathogens. Consequently, their bacteriophages may have significant impact on human microbial ecology and pathologies. Our aim was to reveal the prevalence and diversity of bacteriophages infecting Aggregatibacter and Haemophilus species that colonize the human body. Genome mining with comparative genomics, screening of clinical isolates, and profiling of metagenomes allowed characterization of 346 phages grouped in 52 clusters and 18 superclusters. Less than 10% of the identified phage clusters were represented by previously characterized phages. Prophage diversity patterns varied significantly for different phage types, host clades, and environmental niches. A more diverse phage community lysogenizes Haemophilus influenzae and Haemophilus parainfluenzae strains than Aggregatibacter actinomycetemcomitans and “Haemophilus ducreyi”. Co-infections occurred more often in “H. ducreyi”. Phages from Aggregatibacter actinomycetemcomitans preferably lysogenized strains of specific serotype. Prophage patterns shared by subspecies clades of different bacterial species suggest similar ecoevolutionary drivers. Changes in frequencies of DNA uptake signal sequences and guanine–cytosine content reflect phage-host long-term coevolution. Aggregatibacter and Haemophilus phages were prevalent at multiple oral sites. Together, these findings should help exploring the ecoevolutionary forces shaping virus-host interactions in the human microbiome. Putative lytic phages, especially phiKZ-like, may provide new therapeutic options.

Aggregatibacter actinomycetemcomitans (Aa) Under the Radar: Myths and Misunderstandings of Aa and Its Role in Aggressive Periodontitis

Aggregatibacter actinomycetemcomitans (Aa) is a low-abundance Gram-negative oral pathobiont that is highly associated with a silent but aggressive orphan disease that results in periodontitis and tooth loss in adolescents of African heritage. For the most part Aa conducts its business by utilizing strategies allowing it to conceal itself below the radar of the host mucosal immune defense system. A great deal of misinformation has been conveyed with respect to Aa biology in health and disease. The purpose of this review is to present misconceptions about Aa and the strategies that it uses to colonize, survive, and evade the host. In the process Aa manages to undermine host mucosal defenses and contribute to disease initiation. This review will present clinical observational, molecular, and interventional studies that illustrate genetic, phenotypic, and biogeographical tactics that have been recently clarified and demonstrate how Aa survives and suppresses host mucosal defenses to take part in disease pathogenesis. At one point in time Aa was considered to be the causative agent of Localized Aggressive Periodontitis. Currently, it is most accurate to look at Aa as a community activist and necessary partner of a pathogenic consortium that suppresses the initial host response so as to encourage overgrowth of its partners. The data for Aa's activist role stems from molecular genetic studies complemented by experimental animal investigations that demonstrate how Aa establishes a habitat (housing), nutritional sustenance in that habitat (food), and biogeographical mobilization and/or relocation from its initial habitat (transportation). In this manner Aa can transfer to a protected but vulnerable domain (pocket or sulcus) where its community activism is most useful. Aa's “strategy” includes obtaining housing, food, and transportation at no cost to its partners challenging the economic theory that “there ain't no such thing as a free lunch.” This “strategy” illustrates how co-evolution can promote Aa's survival, on one hand, and overgrowth of community members, on the other, which can result in local host dysbiosis and susceptibility to infection.

Interplay between P. gingivalis, F. nucleatum and A. actinomycetemcomitans in murine alveolar bone loss, arthritis onset and progression

Increasing evidence supports the association of periodontitis with rheumatoid arthritis. Even though a prominent role has been postulated for Porphyromonas gingivalis, many bacterial species contribute to the pathogenesis of periodontal disease. We therefore investigated the impact of Porphyromonas gingivalis as well as other major pathobionts on the development of both, periodontitis and arthritis in the mouse. Pathobionts used - either alone or in combination - were Porphyromonas gingivalis, Fusobacterium nucleatum and Aggregatibacter actinomycetemcomintans. Periodontitis was induced via oral gavage in SKG, DBA/1 and F1 (DBA/1 × B10.Q) mice and collagen-induced arthritis was provoked via immunization and boost with bovine collagen type II. Alveolar bone loss was quantified via micro computed tomography, arthritis was evaluated macroscopically and histologically and serum antibodies were assessed. Among the strains tested, only F1 mice were susceptible to P. gingivalis induced periodontitis and showed significant alveolar bone loss. Bone loss was paralleled by antibody titers against P. gingivalis. Of note, mice inoculated with the mix of all three pathobionts showed less alveolar bone loss than mice inoculated with P. gingivalis alone. However, oral inoculation with either F. nucleatum or A. actinomycetemcomintans alone accelerated subsequent arthritis onset and progression. This is the first report of a triple oral inoculation of pathobionts combined with collagen-induced arthritis in the mouse. In this interplay and this particular genetic setting, F. nucleatum and A. actinomycetemcomitans exerted a protective impact on P. gingivalis induced alveolar bone loss. By themselves they did not induce periodontitis yet accelerated arthritis onset and progression.

Effect of total sonicated Aggregatibacter actinomycetemcomitans fragments on gingival stem/progenitor cells

Background

Aggregatibacter-actinomycetemcomitans (A.actinomycetemcomitans) are strongly associated with localized-aggressive-periodontitis (LAgP). The study’s aim was to test for the first time the effect of total sonicated A.actinomycetemcomitans-bacterial-fragments on gingival mesenchymal stem/progenitor cells’ (G-MSCs) proliferation and regenerative gene expression in-vitro.

Material and Methods

G-MSCs were isolated, characterized, expanded and stimulated by total sonicated A.actinomycetemcomitans-bacterial-fragments (0 (negative-control), 15, 60, 120 and 240µg/ml; serovar-b; n=6/group). Cellular proliferation and NF-κβ (NFKB1), Alkaline Phosphatase (ALPL), Collagen-I (COL1A1), Collagen-III (COL3A1), Osteonectin (SPARC) and Osteopontin (SPP1) m-RNA expression were assessed via reverse-transcription-polymerase-chain-reaction (RT-PCR) at 24, 48 and 72 hours and CFUs-ability evaluated at twelve days.

Results

G-MSCs demonstrated stem/progenitor cells’ characteristics. A.actinomycetemcomitans-bacterial-fragments (up to 72 hours) resulted in marked G-MSCs’ proliferation over-time (p<0.001) and elevated NFKB1 (p=0.017), COL1A1 (p=0.025), SPARC (p=0.025), decreased ALPL (p=0.017), with no significant differences for COL3A1 and SPP1 expression or stimulation times (p>0.05; Friedman-test). Longer-term stimulation for twelve days reduced G-MSCs’ CFUs.

Conclusions

Sonicated A.actinomycetemcomitans-bacterial-fragments’ exert beneficial short-term effects on G-MSCs’ proliferative and non-mineralized tissue forming aptitude. Results shed new light on the importance of periodontal treatment for LAgP patients, using power driven sonic/ultrasonic devices, which, in addition to reducing the subgingival microbial load, produces cell-stimulatory A.actinomycetemcomitans-bacterial-fragments, with positive attributes on tissue reparative/regenerative responses of tissue resident stem/progenitor cells in their niche.

Key words:Ultrasonic, Aggregatibacter actinomycetemcomitans, stem cells, gingiva, Aggressive periodontitis.

Development of novel electrospun dual-drug fiber mats loaded with a combination of ampicillin and metronidazole

OBJECTIVE

Our study was performed with the aim of preparing electrospun polylactide fibers with a combination of ampicillin (AMP) and metronidazole (MNZ) and investigating their drug release behavior and the antibacterial effect on Aggregatibacter actinomycetemcomitans and other oral pathogens.

METHODS

AMP and MNZ were integrated as a combination in two separate fibers (dual fiber mats - DFW mix) of electrospun PLA fiber mats by means of multijet electrospinning and in a single fiber (single fiber mats - SFW mix). HPLC (high-performance liquid chromatography) was used to measure the released drug quantities. Agar diffusion tests were used to determine the antibacterial effect of the eluates on A. actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis and Enterococcus faecalis. The neutral red test was made to examine the cytocompatibility of the eluates with human gingival fibroblasts (hGFs).

RESULTS

The release of the active agents varied with the antibiotic concentrations initially used in the fiber mats, but also with the distribution of the active agents in one or two fibers. Of the total quantity of MNZ (AMP), the SFW mix fiber mats released >60% (>70%) within a span of 5min, and 76% (71%) after 96h. With these drug concentrations released by the fiber mats (≥5m%), an antibacterial effect was achieved on A. actinomycetemcomitans and on all other species tested. Fiber mats and their eluates have no cytotoxic influence on human gingival fibroblasts (hGFs).

SIGNIFICANCE

Electrospun AMP/MNZ-loaded polymer fibers are a potential drug delivery system for use in periodontal and endodontic infections.

Profound Effects of Aggregatibacter actinomycetemcomitans Leukotoxin Mutation on Adherence Properties Are Clarified in in vitro Experiments

Leukotoxin (Ltx) is a prominent virulence factor produced by Aggregatibacter actinomycetemcomitans, an oral microorganism highly associated with aggressive periodontitis. Ltx compromises host responsiveness by altering the viability of neutrophils, lymphocytes, and macrophages. Previously, we developed a Rhesus (Rh) monkey colonization model designed to determine the effect of virulence gene mutations on colonization of A. actinomycetemcomitans. Unexpectedly, an A. actinomycetemcomitans leukotoxin (ltxA) mutant (RhAa-VS2) failed to colonize in the Rh model. No previous literature suggested that Ltx was associated with A. actinomycetemcomitans binding to tooth surfaces. These results led us to explore the broad effects of the ltxA mutation in vitro. Results indicated that LtxA activity was completely abolished in RhAa-VS2 strain, while complementation significantly (P<0.0001) restored leukotoxicity compared to RhAa-VS2 strain. RT-PCR analysis of ltx gene expression ruled out polar effects. Furthermore, binding of RhAa-VS2 to salivary-coated hydroxyapatite (SHA) was significantly decreased (P<0.0001) compared to wild type RhAa3 strain. Real time RT-PCR analysis of the genes related to SHA binding in RhAa-VS2 showed that genes related to binding were downregulated [rcpA (P = 0.018), rcpB (P = 0.02), tadA (P = 0.002)] as compared to wild type RhAa3. RhAa-VS2 also exhibited decreased biofilm depth (P = 0.008) and exo-polysaccharide production (P<0.0001). Buccal epithelial cell (BEC) binding of RhAa-VS2 was unaffected. Complementation with ltxA restored binding to SHA (P<0.002) but had no effect on biofilm formation when compared to RhAa3. In conclusion, mutation of ltxA diminished hard tissue binding in vitro, which helps explain the previous in vivo failure of a ltxA knockout to colonize the Rh oral cavity. These results suggest that; 1) one specific gene knockout (in this case ltxA) could affect other seemingly unrelated genes (such as rcpA, rcpB tadA etc), and 2) some caution should be used when interpreting the effect attributed to targeted gene mutations when seen in a competitive in vivo environment.

Aggregatibacter actinomycetemcomitans: virulence of its leukotoxin and association with aggressive periodontitis

Periodontitis is an infection-induced inflammatory disease that causes loss of the tooth supporting tissues. Much focus has been put on comparison of the microbial biofilm in the healthy periodontium with the diseased one. The information arising from such studies is limited due to difficulties to compare the microbial composition in these two completely different ecological niches. A few longitudinal studies have contributed with information that makes it possible to predict which individuals who might have an increased risk of developing aggressive forms of periodontitis, and the predictors are either microbial or/and host-derived factors. The most conspicuous condition that is associated with disease risk is the presence of Aggregatibacter actinomycetemcomitans at the individual level. This Gram-negative bacterium has a great genetic variation with a number of virulence factors. In this review we focus in particular on the leukotoxin that, based on resent knowledge, might be one of the most important virulence factors of A. actinomycetemcomitans.

An In Vitro Comparison of Antimicrobial Effects of Curcumin-Based Photodynamic Therapy and Chlorhexidine, on Aggregatibacter actinomycetemcomitans

INTRODUCTION

Considering the importance of prevention in periodontal diseases and the important role of Aggregatibacter actinomycetemcomitans in induction and progression of these diseases, the aim of the present in vitro study was to compare the antimicrobial effects of chlorhexidine digluconate (CHX), curcumin and light-emitting diode (LED) laser, on this bacterium.

METHODS

Antimicrobial activity of curcumin (5 mg/ml), CHX (2%), LED (120 J/cm(2)) and LED + curcumin (120 J/cm(2) + 2.5 mg/ml) against A. actinomycetemcomitans were tested in vitro, using micro-broth dilution test. One-way analysis of variance (ANOVA) and Tukey's HSD tests served for statistical analysis.

RESULTS

Regarding the minimum inhibitory concentration (MIC), CHX had a significantly lower MIC than curcumin (P < 0.05). Sorted out by bacterial growth from lowest to highest, were CHX, LED + curcumin, curcumin, and LED groups. All the differences were found to be statistically significant (P < 0.05) except for the LED group.

CONCLUSION

We conclude that curcumin is an effective substance in preventing the growth of A. actinomycetemcomitans, whose impact is reinforced when used simultaneously with photodynamic therapy (PDT).

Colonization and Persistence of Labeled and "Foreign" Strains of Aggregatibacter actinomycetemcomitans Inoculated into the Mouths of Rhesus Monkeys

Aggregatibacter actinomycetemcomitans (Aa) is a pathobiont and part of a consortium of bacteria that can lead to periodontitis in humans. Our aim was to develop a model for oral inoculation of labeled Aa into a suitable host in order to study Aa traits and ecological factors that either enhance or repress its persistence. Primate species were screened for Aa to select a host for colonization studies. Macaca mulatta (Rhesus/Rh) was selected. Rh Aa strains were isolated, subjected to sequencing and functional analysis for comparison to human strains. "Best" methods for microbial decontamination prior to inoculation were assessed. Three groups were studied; Group 1 (N=5) was inoculated with Aa Spectinomycin resistant (SpecR) Rh strain 4.35, Group 2 (N=5) inoculated with Aa SpecR human strain IDH 781, and Group 3 (N=5) the un-inoculated control. Repeated feeding with pancakes spiked with SpecRAa followed high dose oral inoculation. Cheek, tongue, and plaque samples collected at baseline 1, 2, 3, and 4 weeks after inoculation were plated on agar; 1) selective for Aa, 2) enriched for total counts, and 3) containing 50 µg/ml of Spec. Aa was identified by colonial morphology and DNA analysis. Rh and human Aa had > 93-98 % genome identity. Rh Aa attached to tissues better than IDH 781 in vitro (p < 0.05). SpecR IDH 781 was not recovered from any tissue at any time; whereas, RhSpecR 4.35 was detected in plaque, but never tongue or cheek, in all monkeys at all times (> 1 × 10⁵ colonies/ml; p < 0.001). In conclusion, the primate model provides a useful platform for studying integration of Aa strains into a reduced but established oral habitat. Primate derived SpecRAa was consistently detected in plaque at all collection periods; however, human derived Aa was never detected. The model demonstrated both microbial as well as tissue specificity.

Integration of non-oral bacteria into in vitro oral biofilms

Biofilms are polymicrobial communities that grow on surfaces in nature. Oral bacteria can spontaneously form biofilms on the surface of teeth, which may compromise the health of the teeth, or their surrounding (periodontal) tissues. While the oral bacteria exhibit high tropism for their specialized ecological niche, it is not clear if bacteria that are not part of the normal oral microbiota can efficiently colonize and grow within oral biofilms. By using an in vitro "supragingival" biofilm model of 6 oral species, this study aimed to investigate if 3 individual bacterial species that are not part of the normal oral microbiota (Eschericia coli, Staphylococcus aureus, Enterococcus faecails) and one not previously tested oral species (Aggregatibacter actinomycetemcomitans) can be incorporated into this established supragingival biofilm model. Staphylococcus aureus and A. actinomycetemcomitans were able to grow efficiently in the biofilm, without disrupting the growth of the remaining species. They localized in sparse small aggregates within the biofilm mass. Enterococcus faecalis and E. coli were both able to populate the biofilm at high numbers, and suppressed the growth of A. oris and S. mutants. Enterococcus faecalis was arranged in a chain-like conformation, whereas E. coli was densely and evenly spread throughout the biofilm mass. In conclusion, it is possible for selected species that are not part of the normal oral microbiota to be introduced into an oral biofilm, under the given experimental micro-environmental conditions. Moreover, the equilibrated incorporation of A. actinomycetemcomitans and S. aureus in this oral biofilm model could be a useful tool in the study of aggressive periodontitis and peri-implantitis, in which these organisms are involved, respectively.

Inactivation of Aggregatibacter actinomycetemcomitans by two different modalities of photodynamic therapy using Toluidine blue O or Radachlorin as photosensitizers: an in vitro study

Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is one of the periodontopathogens strongly associated with aggressive periodontitis. The aim of this investigation was to compare the effect of laser and light-emitting diode on the photodynamic inactivation of A. actinomycetemcomitans. Eighty-four samples of bacterial suspensions (200 μL) were prepared and divided in seven groups: control group (no treatment), laser group (indium-gallium-aluminum-phosphate laser with wavelength of 662 ± 0.1 nm, energy density of 6 j/cm(2), and irradiation time of 34 s), light-emitting diode (LED) group (wavelength 625-635 nm, energy density 6 j/cm(2), time of irradiation 30 s), Toluidine blue O (TBO) group (0.1 mg/mL), Radachlorin group (0.1 %), Radachlorin + laser group (after pre-irradiation time of 10 min, laser was irradiated), and TBO + LED group (after preirradiation time of 10 min, LED was irradiated). Then, 100 μL of each sample was cultured in brain heart infusion (BHI) plates and incubated for 48-72 h in microaerophilic atmosphere for colony counting. Application of Radachlorin + laser resulted in a significant decrease in the concentration of A. actinomycetemcomitans (P values <0.05). Photodynamic therapy with laser + Radachlorin was more effective than that of LED + TBO in suppression of this microorganism (P value <0.05). Within the limits of this study, it can be concluded that photodynamic inactivation using laser and Radachlorin was more effective than that of LED and TBO in eradication of A. actinomycetemcomitans.

Porphyromonas gingivalis gingipain is involved in the detachment and aggregation of Aggregatibacter actinomycetemcomitans biofilm

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are major periodontal pathogens that cause several types of periodontal disease. Our previous study suggested that P. gingivalis gingipains secreted in the subgingival environment are related to the detachment of A.actinomycetemcomitans biofilms. However, it remains unclear whether arginine-specific cysteine proteinase (Rgp) and lysine-specific proteinase (Kgp) play different roles in the detachment of A. actinomycetemcomitans biofilm. The aim of this study was to investigate possible disruptive roles of Kgp and Rgp in the aggregation and attachment of A. actinomycetemcomitans. While P. gingivalis ATCC33277 culture supernatant has an ability to decrease autoaggregation and coaggregation of A. actinomycetemcomitans cells, neither the boiled culture supernatant of ATCC33277 nor the culture supernatant of KDP136 showed this ability. The addition of KYT-1 and KYT-36, specific inhibitors of Rgp and Kgp, respectively, showed no influence on the ability of P. gingivalis culture supernatant. The result of gelatin zymography suggested that other proteases processed by gingipains mediated the decrease of A. actinomycetemcomitans aggregations. We also examined the biofilm-destructive effect of gingipains by assessing the detachment of A. actinomycetemcomitans from polystyrene surfaces. Scanning electron microscope analysis indicated that A. actinomycetemcomitans cells were detached by P. gingivalis Kgp. The quantity of A. actinomycetemcomitans in biofilm was decreased in co-culture with P. gingivalis. However, this was not found after the addition of KYT-36. These findings suggest that Kgp is a critical component for the detachment and decrease of A. actinomycetemcomitans biofilms.

Role of salivary epithelial toll-like receptors 2 and 4 in modulating innate immune responses in chronic periodontitis

BACKGROUND AND OBJECTIVE

Chronic periodontitis is initiated by sequential colonization with a broad array of bacteria and is perpetuated by an immune-inflammatory response to the changing biofilm. Host recognition of microbes is largely mediated by toll-like receptors (TLRs), which interact with conserved pathogen-associated molecular patterns. Based on ligand recognition, TLR-2 and TLR-4 interact with most periodontal pathogens. Extracrevicular bacterial reservoirs, such as the oral epithelial cells, contribute to the persistence of periodontitis. Human saliva is a rich source of oral epithelial cells that express functional TLRs. In this study we investigated the role of salivary epithelial cell (SEC) TLR-2 and TLR-4 in patients with generalized chronic periodontitis.

MATERIAL AND METHODS

Unstimulated whole saliva (UWS) was collected from patients with generalized chronic periodontitis and from healthy individuals after obtaining informed consent. Epithelial cells isolated from each UWS sample were assessed for TLR-2, TLR-4, peptidoglycan recognition protein (PGRP)-3 and PGRP-4 by quantitative real-time PCR. In addition, the SECs were stimulated in vitro with microbial products for up to 24 h. The culture supernatant was assessed for cytokines by ELISA.

RESULTS

Stimulation with TLR-2- or TLR-4-specific ligands induced cytokine secretion with differential kinetics and up-regulated TLR2 and TLR4 mRNAs, respectively, in cultures of SECs from patients with periodontitis. In addition, the SECs from patients with periodontitis exhibited reduced PGRP3 and PGRP4 mRNAs, the TLR-responsive genes with antibacterial properties.

CONCLUSION

SECs derived from the UWS of patients with chronic periodontitis are phenotypically distinct and could represent potential resources for assessing the epithelial responses to periodontal pathogens in the course of disease progression and persistence.

Can salivary activity predict periodontal breakdown in A. actinomycetemcomitans infected adolescents?

OBJECTIVE

While Aggregatibacter actinomycetemcomitans (Aa) is highly associated with localised aggressive periodontitis (LAP) many Aa-carriers do not develop LAP. This study was designed to determine whether specific salivary factors could distinguish between subjects who have Aa initially and remain healthy (H/AA) as compared to those who develop LAP (LAP/AA).

DESIGN

H/AA subjects and healthy controls with no Aa (H) were enrolled in a longitudinal cohort study to investigate initiation of bone loss (LAP) over 3 years. After detection of LAP, stored saliva from 10 H, 10 H/AA, and 10 LAP/AA subjects was thawed, processed, and tested for (1) lactoferrin (Lf) concentration and iron levels; (2) agglutination of Aa; (3) killing of Gram-positive bacteria.

RESULTS

LAP/AA saliva levels of Lf iron were low prior to and after bone loss (3.6+1.7ngFe/μg) (LAP/AA vs. H and H/AA p≤0.01). Saliva from H/AA subjects caused Aa to agglutinate significantly more than H or LAP/AA saliva (p≤0.01). LAP/AA saliva killed Streptococcus mutans, Streptococcus sanguis and Lactobacillus in vitro by >83%. Saliva from H individuals killed these bacteria by <3.3% (LAP/AA vs. H; p≤0.01). H/AA killing was intermediate.

CONCLUSION

LAP/AA saliva showed: low levels of Lf iron, minimal Aa agglutinating activity, and high killing activity against Gram-positive bacteria. Aa-positive healthy saliva (H/AA) showed: higher levels of Lf iron, maximal Aa agglutinating activity, and moderate killing of Gram-positive bacteria. A salivary activity profile can distinguish between subjects who are Aa-positive and remain healthy from those who develop LAP.

Porphyromonas gingivalis displays a competitive advantage over Aggregatibacter actinomycetemcomitans in co-cultured biofilm

BACKGROUND AND OBJECTIVE

Biofilm formation occurs through the events of cooperative growth and competitive survival among multiple species. Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are important periodontal pathogens. The aim of this study was to demonstrate competitive or cooperative interactions between these two species in co-cultured biofilm.

MATERIAL AND METHODS

P. gingivalis strains and gingipain mutants were cultured with or without A. actinomycetemcomitans. Biofilms formed on glass surfaces were analyzed by crystal violet staining and colony counting. Preformed A. actinomycetemcomitans biofilms were treated with P. gingivalis culture supernatants. Growth and proteolytic activities of gingipains were also determined.

RESULTS

Monocultured P. gingivalis strains exhibited a range of biofilm-formation abilities and proteolytic activities. The ATCC33277 strain, noted for its high biofilm-formation ability and proteolytic activity, was found to be dominant in biofilm co-cultured with A. actinomycetemcomitans. In a time-resolved assay, A. actinomycetemcomitans was primarily the dominant colonizer on a glass surface and subsequently detached in the presence of increasing numbers of ATCC33277. Detachment of preformed A. actinomycetemcomitans biofilm was observed by incubation with culture supernatants from highly proteolytic strains.

CONCLUSION

These results suggest that P. gingivalis possesses a competitive advantage over A. actinomycetemcomitans. As the required biofilm-formation abilities and proteolytic activities vary among P. gingivalis strains, the diversity of the competitive advantage is likely to affect disease recurrence during periodontal maintenance.

Stick to your gums: mechanisms of oral microbial adherence

Studies on the adherence properties of oral bacteria have been a major focus in microbiology research for several decades. The ability of bacteria to adhere to the variety of surfaces present in the oral cavity, and to become integrated within the resident microbial communities, confers growth and survival properties. Molecular analyses have revealed several families of Gram-positive bacterial surface proteins, including serine-rich repeat, antigen I/II, and pilus families, that mediate adherence to a variety of salivary and oral bacterial receptors. In Gram-negative bacteria, pili, auto-transporters, and extracellular matrix-binding proteins provide components for host tissue recognition and building of complex microbial communities. Future studies will reveal in greater detail the binding pockets for these adhesin families and their receptors. This information will be crucial for the development of new inhibitors or vaccines that target the functional regions of bacterial proteins that are involved in colonization and pathogenesis.