Aggregatibacter actinomycetemcomitans serotypes, the JP2 clone and cytolethal distending toxin genes in a Thai population

Virulence Factors of the Periodontal Pathogens: Tools to Evade the Host Immune Response and Promote Carcinogenesis

Periodontitis is the most common chronic, inflammatory oral disease that affects more than half of the population in the United States. The disease leads to destruction of the tooth-supporting tissue called periodontium, which ultimately results in tooth loss if uncured. The interaction between the periodontal microbiota and the host immune cells result in the induction of a non-protective host immune response that triggers host tissue destruction. Certain pathogens have been implicated periodontal disease formation that is triggered by a plethora of virulence factors. There is a collective evidence on the impact of periodontal disease progression on systemic health. Of particular interest, the role of the virulence factors of the periodontal pathogens in facilitating the evasion of the host immune cells and promotion of carcinogenesis has been the focus of many researchers. The aim of this review is to examine the influence of the periodontal pathogens Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), Porphyromonas gingivalis (P. gingivalis), and Fusobacterium nucleatum (F. nucleatum) in the modulation of the intracellular signaling pathways of the host cells in order to evade the host immune response and interfere with normal host cell death and the role of their virulence factors in this regard.

Prevalence of Aggregatibacter actinomycetemcomitans and Periodontal Findings among 14 to 15-Year Old Danish Adolescents: A Descriptive Cross-Sectional Study

Aggregatibacter actinomycetemcomitans (Aa) is a keystone pathogen associated with periodontitis in adolescents. The knowledge on the prevalence of Aa and periodontitis among adolescents in Northern Europe is sparse. A total of 525 14- to 15-year-old adolescents from the municipality of Aarhus, Denmark, underwent a full-mouth clinical examination. Plaque score (PS), bleeding on probing (BOP), probing pocket depth (PPD), and clinical attachment loss (CAL) were recorded. Subgingival plaque samples (SPS) and stimulated saliva samples (SSS) were collected and analyzed for the presence of JP2 and non-JP2 genotypes of Aa using real-time PCR. A total of 70 (13.3%) individuals were positive for Aa, with 17 found in SPS, 19 in SSS, and 35 in both. The highly leukotoxic JP2 genotype of Aa was not detected. The individuals positive for Aa in both SPS and SSS had poorer periodontal outcomes (PPD and CAL) than individuals without Aa and individuals carrying Aa in either SPS or SSS only. In conclusion, 13% of 14- to 15-year-old Danish adolescents were positive for Aa, and the presence of Aa in both SPS and SSS was associated with poorer periodontal outcomes.

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.

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.

Profiling of Aggregatibacter actinomycetemcomitans Serotypes B and C and the genotypes in periodontal health and disease

BACKGROUND

A. actinomycetemcomitans is prevalent in periodontitis but is found in some periodontally healthy individuals as well. Certain serotypes of the organism have shown to determine severity of the disease. The distribution of serotype and genotype is affected by geographic and ethnic variation. Therefore, the present study was aimed to detect serotypes b & c of A. actinomycetemcomitans and the genotypes and find its correlation with periodontal status.

MATERIALS AND METHODS

A total of 75 subjects (25 aggressive periodontitis, 25 chronic periodontitis and 25 periodontally healthy) in age range of 14-55 yrs were included. Subgingival plaque samples were collected and checked for the presence of A. actinomycetemcomitans. Following isolation of the organism, detection of the serotype b or c was done by multiplex PCR. Genotyping of A. actinomycetemcomitans was done by arbitrarily primed PCR(polymerase chain reaction).

RESULTS

Out of 75 plaque samples, 35(46.66%) tested positive for A. actinomycetemcomitans. Serotype c was detected in 19/35 (54.28%), whereas serotype b alone was not detected in any of the samples. Two samples were positive for both the serotypes (b and c) (5.71%) and 14 (40%) were untypeable. 14 different arbitrarily primed PCR genotypes were obtained among 35 A. actinomycetemcomitans isolates.

CONCLUSION

Serotype c was predominant in periodontally diseased as well as periodontally healthy individuals. An association could be present between genotype - serotype and genotype - periodontal status.

Serotypes of Aggregatibacter actinomycetemcomitans in relation to periodontal status and assessment of leukotoxin in periodontal disease: A clinico-microbiological study

Context:

Aggregatibacter actinomycetemcomitans (A.a) serotypes may add some important information of the pathogenetic background of periodontal infections. A.a leukotoxin is an important virulence factor in the pathogenesis of periodontal disease and its rate of progression. When compared to minimally leukotoxic strains, variants of A.a highly leukotoxic strains produce 10–20 times more leukotoxin.

Aims:

The aim of the present study was to detect serotypes a, b, c, d, and e of A.a its leukotoxin and find its correlation with periodontal status.

Settings and Design:

Microbiological analysis and cross-sectional study.

Materials and Methods:

A total of 80 subjects (40 chronic periodontitis and 40 aggressive periodontitis) in the age range of 14–55 years were selected. Subgingival plaque samples were collected and checked for the presence of A.a. Following isolation of the organism, detection of the serotypes and leukotoxin assessment was done.

Statistical Analysis Used:

The proportions of A.a were calculated using descriptive statistics in terms of percentage. Chi-square test was used to find association between serotype, leukotoxin, and periodontal disease in individual group.

Results:

Out of 80 plaque samples, 45% tested positive for A.a. serotype b was detected in 33.33%, whereas serotype e in 8.33% samples and serotype c in 2.77% samples. Serotypes a and d were not detected in any of the samples. A combination of serotypes was seen in 47.22% of the sites. Of these 76.47% showed a combination of 2 serotypes, while 23.52%showed a combination of 3 serotypes. 8.33% showed untypable serotype. All samples had low-toxic variants of A.a.

Conclusions:

Serotype b and serotype e were predominant in chronic periodontitis, and serotype b was predominant in aggressive periodontitis. An association could be present between serotype and periodontal disease.

Pro-inflammatory cytokine responses in human gingival epithelial cells after stimulation with cell wall extract of Aggregatibacter actinomycetemcomitans subtypes

Varying cytokine responses of human gingival epithelial cells (HGECs) by Aggregatibacter actinomycetemcomitans subtypes have been found. Most studies have used reference strains, whereas a few has evaluated the cytokine expression in response to clinical subtypes of this bacterial species. This study aimed to examine whether there was any difference in cytokine responses of HGECs stimulated with cell wall extract (CWE) from A. actinomycetemcomitans subtypes included clinical strains from Thai adult periodontitis, various serotypes and non-serotypeable strains, strains from deep or shallow pockets, and reference serotype strains. Totally 50 clinical strains and 7 reference strains of A. actinomycetemcomitans were analyzed for the expression of IL-1β, IL-6, IL-8, and TNF-α mRNAs in HGECs by real time-PCR, and the IL-8 concentrations in cell-free supernatant measured using ELISA. An in vitro effect of released IL-8 on neutrophil migration was examined using transwell chambers. Result showed that among four cytokines studied, IL-8 mRNA was highly up-regulated by both clinical and reference strains. Serotype f revealed the highest expression compared to other serotypes. The JP2-like leukotoxin promoter gene and non-serotypeable (NS1 and NS2) demonstrated lower IL-8 responses compared to serotypeable strains, and IL-8 responses upon stimulation with clinical strains from deep pockets were also significantly lower than those isolated from shallow pockets (P < 0.01). Our findings suggest that the clinical isolates of A. actinomycetemcomitans associating with deep pockets, JP2-like leukotoxin promoter gene, NS1, and NS2 may interfere neutrophil function via minimal and immunosuppressing IL-8 responses, which may enhance their survival and virulence.

Prevalence and comparative analysis of the type IV secretion system in Aggregatibacter actinomycetemcomitan

BACKGROUD/PURPOSE

Aggregatibacter actinomycetemcomitans has emerged as one of the aetiological agents in periodontal disease. Although Type IV secretion systems (T4SSs) are widely distributed in many bacteria, the genetic features and distribution of T4SSs in A. actinomycetemcomitans remain unclear. In this study, we investigated the prevalence of A. actinomycetemcomitans serotypes and their T4SSs in a Taiwanese population.

METHODS

A comparative analysis of 20 A. actinomycetemcomitans genomes and their T4SSs deposited in GenBank was performed. One hundred subjects, including 20 periodontitis and 80 normal subjects, were enrolled and PCR identification of A. actinomycetemcomitans serotypes and T4SS genes were performed.

RESULTS

Of 100 subjects, serotypes C (22%) and E (11%) were most common. In addition, T4SSs were distributed in all of the serotypes. The prevalence of T4SSs and their location in plasmids in periodontitis subjects were 1.28-2 fold higher but not significantly different compared to normal subjects. Of 20 A. actinomycetemcomitans genomes, only ten with complete T4SS modules could be detected, which was highly correlated with localized aggressive periodontitis (p < 0.1). Nine of ten T4SS modules were from periodontitis subjects. Phylogenetic analysis of 10 T4SSs in A. actinomycetemcomitans showed that they were clustered into two groups, T4SS_AaI and T4SS_AaII, with only T4SS_AaI appearing in the Taiwanese subjects.

CONCLUSION

A. actinomycetemcomitans strains with different serotypes carrying T4SS_AaI are widely distributed in a Taiwanese population. This is the first report to show the distribution and detailed comparative genomics of T4SSs in A. actinomycetemcomitans.

Characterization and serotype distribution of Aggregatibacter actinomycetemcomitans: Relationship of serotypes to herpesvirus and periodontal status in Indian subjects

BACKGROUND

The virulence of Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) in any individual depends on the type of strain of this bacterium. To our knowledge, there have been no studies reported in Indian subjects about A. actinomycetemcomitans serotype occurrence, co-existence with herpes virus and the possible influence of such co-existence on periodontal pathology.

METHODS

Subjects for this study were a subset of a larger study to identify the prevalence of A. actinomycetemcomitans in chronic periodontitis. A total of 63 subjects (12 periodontally healthy and 51 with chronic periodontitis) who were positive for A. actinomycetemcomitans were serotyped for strain-level identification. The presence of Human Cytomegalovirus (CMV) and Epstein-Barr virus (EBV) was tested in subgingival plaque samples by polymerase chain reaction.

RESULTS

All five serotypes a to e were detected. Of the samples analyzed 38.09% harbored a single serotype, 36.5% had two serotypes, 6.3% demonstrated three and 4.7% demonstrated four serotypes. None of the samples showed presence of JP2 strain. Serotypes b, c, and e were most frequently identified in these individuals (46.03%, 36.5% and 38.09% respectively). Presence of serotypes b and c and absence of serotype d was associated with increased PD and CAL. Among 63 samples analyzed, 11 samples had CMV, four samples had EBV and nine samples had both these viruses. The PD and CAL were significantly higher (p = 0.04) when a combination of CMV and one of the serotypes was present indicating a pathological role of the coexistence.

CONCLUSION

Multiple serotypes are associated with chronic periodontitis in Indians, however, JP2 strains are not detectable in this cohort. Presence of multiple serotypes and a combination of any serotype with herpesvirus is associated with greater severity of the disease.

Differential human Th22-lymphocyte response triggered by Aggregatibacter actinomycetemcomitans serotypes

OBJECTIVE

In Aggregatibacter actinomycetemcomitans, different serotypes have been described based on lipopolysaccharide (LPS) antigenicity. When T lymphocytes were stimulated with these serotypes, different patterns of T-helper (Th)1 and Th17-type of immune responses were reported. Recently, two new Th phenotypes have been described and named Th9 and Th22 lymphocytes; however, their role in the pathogenesis of periodontitis remains unclear. This study aimed to investigate the potential Th9 and/or Th22 lymphocyte responses when stimulated with autologous dendritic cells infected with different A. actinomycetemcomitans serotypes.

METHODS

Monocyte-derived dendritic cells and naïve CD4⁺ T lymphocytes were obtained from healthy donors and stimulated with different serotypes of A. actinomycetemcomitans at a multiplicity of infection MOI=10² or their purified LPS (10-50ng/ml). The levels for the Th9 and Th22-associated cytokines, as well as the transcription factor master-switch genes implied in their differentiation Spi-B and AhR, were quantified by qPCR and ELISA.

RESULTS

When stimulated with the serotype b of A. actinomycetemcomitans, higher levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α were detected in dendritic cells, as well as higher levels of IL-22 and AhR were detected in T lymphocytes, when compared with stimulation with the other serotypes.

CONCLUSIONS

The serotype b of A. actinomycetemcomitans has a higher capacity of trigger Th22-type of immune response in both dendritic cells and T lymphocytes. These data allow us to suggest that, when the serotype b of A. actinomycetemcomitans is a significant part of the subgingival biofilm, the Th22 polarization might be triggered within the periodontal lesion.

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.

A Cytolethal Distending Toxin Variant from Aggregatibacter actinomycetemcomitans with an Aberrant CdtB That Lacks the Conserved Catalytic Histidine 160

The periodontopathogen Aggregatibacter actinomycetemcomitans synthesizes several virulence factors, including cytolethal distending toxin (CDT). The active CDT holoenzyme is an AB-type tripartite genotoxin that affects eukaryotic cells. Subunits CdtA and CdtC (B-components) allow binding and intracellular translocation of the active CdtB (A-component), which elicits nuclear DNA damage. Different strains of A. actinomycetemcomitans have diverse virulence genotypes, which results in varied pathogenic potential and disease progression. Here, we identified an A. actinomycetemcomitans strain isolated from two patients with advance chronic periodontitis that has a regular cdtABC operon, which, however, codes for a unique, shorter, variant of the CdtB subunit. We describe the characteristics of this CdtBΔ116–188, which lacks the intact nuclear localisation signal and the catalytic histidine 160. We show that the A. actinomycetemcomitans DO15 isolate secretes CdtBΔ116–188, and that this subunit cannot form a holotoxin and is also not genotoxic if expressed ectopically in HeLa cells. Furthermore, the A. actinomycetemcomitans DO15 isolate is not toxic, nor does it induce cellular distention upon infection of co-cultivated HeLa cells. Biological significance of this deletion in the cdtB remains to be explained.

Microbiology of aggressive periodontitis

For decades, Aggregatibacter actinomycetemcomitans has been considered the most likely etiologic agent in aggressive periodontitis. Implementation of DNA-based microbiologic methodologies has considerably improved our understanding of the composition of subgingival biofilms, and advanced open-ended molecular techniques even allow for genome mapping of the whole bacterial spectrum in a sample and characterization of both the cultivable and not-yet-cultivable microbiota associated with periodontal health and disease. Currently, A. actinomycetemcomitans is regarded as a minor component of the resident oral microbiota and as an opportunistic pathogen in some individuals. Its specific JP2 clone, however, shows properties of a true exogenous pathogen and has an important role in the development of aggressive periodontitis in certain populations. Still, limited data exist on the impact of other microbes specifically in aggressive periodontitis. Despite a wide heterogeneity of bacteria, especially in subgingival samples collected from patients, bacteria of the red complex in particular, and those of the orange complex, are considered as potential pathogens in generalized aggressive periodontitis. These types of bacterial findings closely resemble those found for chronic periodontitis, representing a mixed polymicrobial infection without a clear association with any specific microorganism. In aggressive periodontitis, the role of novel and not-yet-cultivable bacteria has not yet been elucidated. There are geographic and ethnic differences in the carriage of periodontitis-associated microorganisms, and they need to be taken into account when comparing study reports on periodontal microbiology in different study populations. In the present review, we provide an overview on the colonization of potential periodontal pathogens in childhood and adolescence, and on specific microorganisms that have been suspected for their role in the initiation and progression of aggressive forms of periodontal disease.

Aggregatibacter actinomycetemcomitans, a potent immunoregulator of the periodontal host defense system and alveolar bone homeostasis

Aggregatibacter actinomycetemcomitans is a perio-pathogenic bacteria that has long been associated with localized aggressive periodontitis. The mechanisms of its pathogenicity have been studied in humans and preclinical experimental models. Although different serotypes of A. actinomycetemcomitans have differential virulence factor expression, A. actinomycetemcomitans cytolethal distending toxin (CDT), leukotoxin, and lipopolysaccharide (LPS) have been most extensively studied in the context of modulating the host immune response. Following colonization and attachment in the oral cavity, A. actinomycetemcomitans employs CDT, leukotoxin, and LPS to evade host innate defense mechanisms and drive a pathophysiologic inflammatory response. This supra-physiologic immune response state perturbs normal periodontal tissue remodeling/turnover and ultimately has catabolic effects on periodontal tissue homeostasis. In this review, we have divided the host response into two systems: non-hematopoietic and hematopoietic. Non-hematopoietic barriers include epithelium and fibroblasts that initiate the innate immune host response. The hematopoietic system contains lymphoid and myeloid-derived cell lineages that are responsible for expanding the immune response and driving the pathophysiologic inflammatory state in the local periodontal microenvironment. Effector systems and signaling transduction pathways activated and utilized in response to A. actinomycetemcomitans will be discussed to further delineate immune cell mechanisms during A. actinomycetemcomitans infection. Finally, we will discuss the osteo-immunomodulatory effects induced by A. actinomycetemcomitans and dissect the catabolic disruption of balanced osteoclast-osteoblast-mediated bone remodeling, which subsequently leads to net alveolar bone loss.

Aggregatibacter actinomycetemcomitans serotypes and DGGE subtypes in Thai adults with chronic periodontitis

OBJECTIVE

To investigate the distribution of Aggregatibacter actinomycetemcomitans serotypes and DGGE subtypes among isolates from Thai chronic periodontitis patients.

DESIGN

Forty-four adult Thai periodontitis patients were assessed by a full mouth recording for CAL, PPD, and BOP. Seventy-nine strains of A. actinomycetemcomitans were isolated from deep pockets on selective TSBV agar and 17 strains were isolated from shallow pockets. The strains were serotyped using PCR and subtyped using DGGE.

RESULTS

The prevalence of A. actinomycetemcomitans was 84.1%. Non-serotypeable A. actinomycetemcomitans strains occurred equally frequent as serotypeable (54.5%); serotype a 18.2%, serotype c 15.9%, serotype e 9.1%, and serotype f 11.4%. Serotype b and d were not detected. A JP2 like strain but serotyped as c was isolated from two patients, and another two strains showed an 886bp insertion on the ltx promoter of their A. actinomycetemcomitans isolates. DGGE typing disclosed 16 different subtypes among the non-serotypeable strains. Two of them (NS1 and NS2) were more common (12.7 and 10.1%) among the strains than the other 14 subtypes (˂5.1%). Most patients showed only one subtype (32.4%) but 29.7% had 2 and 3 different subtypes while 8.1% revealed 4 subtypes in one and the same deep pocket.

CONCLUSION

This study showed a greater subtype diversity of A. actinomycetemcomitans predominated by non-serotypeable strains than previously reported in an adult Thai population. It was also revealed for the first time that isolates with a 530bp deletion or 886bp insertion of the ltx promoter were serotyped as serotype c.

Serotype b of Aggregatibacter actinomycetemcomitans increases osteoclast and memory T-lymphocyte activation

During periodontitis, alveolar bone resorption is associated with activation of T helper type 17 (Th17) lymphocytes and receptor activator of nuclear factor-κB ligand (RANKL) -induced osteoclasts. We previously reported that serotype b of Aggregatibacter actinomycetemcomitans has a higher capacity to trigger Th17-type differentiation and function in activated T lymphocytes and its lipopolysaccharide is a more potent immunogen compared with the other serotypes. This study aimed to investigate whether serotype b of A. actinomycetemcomitans induces higher Th17-associated RANKL production, RANKL-induced osteoclast activation, and antigen-specific memory T lymphocyte proliferation. On naive CD4(+) T lymphocytes stimulated with autologous dendritic cells primed with different A. actinomycetemcomitans serotypes, RANKL production, T-bet, GATA-3, RORC2 and Foxp3 expression, RORC2/RANKL intracellular double-expression, TRAP(+) osteoclast activation, and bone resorption were quantified. The frequency of proliferating memory T lymphocytes in response to A. actinomycetemcomitans serotypes was determined in periodontitis and healthy subjects. Naive CD4(+) T lymphocytes stimulated by serotype b-primed dendritic cells elicited higher levels of RANKL, RORC2, TRAP(+) osteoclasts, and bone resorption than the same cells stimulated with the other serotypes. RANKL positively correlated and co-expressed with RORC2. Memory T lymphocytes responding to serotype b were more frequently detected in periodontitis patients than healthy subjects. These results indicate that serotype b of A. actinomycetemcomitans is associated with higher production of RANKL and these increased levels are associated with Th17 lymphocyte induction, osteoclast activation, and bone resorption.

T-lymphocyte phenotype and function triggered by Aggregatibacter actinomycetemcomitans is serotype-dependent

BACKGROUND AND OBJECTIVE

Based on lipopolysaccharide (LPS) antigenicity, different Aggregatibacter actinomycetemcomitans serotypes have been described. Serotype b strains have demonstrated a stronger capacity to trigger cytokine production on dendritic cells (DCs). As DCs regulate the development of T-lymphocyte lineages, the objective of this investigation was to study the response of T lymphocytes after being stimulated with autologous DCs primed with different bacterial strains belonging to the most prevalent serotypes of A. actinomycetemcomitans in humans: a-c.

MATERIAL AND METHODS

Human DCs were primed with increasing multiplicity of infection (10(-1) -10(2) ) or the purified LPS (10-50 ng/mL) of A. actinomycetemcomitans serotypes a-c and then used to stimulate autologous naïve CD4(+) T lymphocytes. The T-helper (Th) type 1, Th2, Th17 and T-regulatory transcription factors T-bet, GATA-3, RORC2 and Foxp3, which are the master-switch genes implied in their specific differentiation, as well as T-cell phenotype-specific cytokine patterns were quantified by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. In addition, the intracellular expression of T-bet/interferon-γ, GATA-3/interleukin-4, RORC2/interleukin-17A and Foxp3/transforming growth factor-β1 was analysed by double staining and flow cytometry.

RESULTS

All the A. actinomycetemcomitans serotypes led to T-lymphocyte activation; however, when T lymphocytes were stimulated with DCs primed with the A. actinomycetemcomitans serotype b strain or their purified LPS, higher levels of Th1- and Th17-associated transcription factors and cytokines were detected compared with similar experiments with the other serotypes.

CONCLUSION

These results demonstrate that serotype b of A. actinomycetemcomitans has a higher capacity of trigger Th1 and Th17 phenotype and function and it was demonstrated that their LPS is a more potent immunogen compared with the other serotypes.

Cytolethal Distending Toxin: A Unique Variation on the AB Toxin Paradigm

Some of the most potent toxins produced by plants and bacteria are members of a large family known as the AB toxins. AB toxins are generally characterized by a heterogenous complex consisting of two protein chains arranged in various monomeric or polymeric configurations. The newest class within this superfamily is the cytolethal distending toxin (Cdt). The Cdt is represented by a subfamily of toxins produced by a group of taxonomically distinct Gram negative bacteria. Members of this subfamily have a related AB-type chain or subunit configuration and properties distinctive to the AB paradigm. In this review, the unique structural and cytotoxic properties of the Cdt subfamily, target cell specificities, intoxication pathway, modes of action, and relationship to the AB toxin superfamily are compared and contrasted.

Pathogenicity of the highly leukotoxic JP2 clone of Aggregatibacter actinomycetemcomitans and its geographic dissemination and role in aggressive periodontitis

For decades, Aggregatibacter actinomycetemcomitans has been associated with aggressive forms of periodontitis in adolescents. In the middle of the 1990s, a specific JP2 clone of A. actinomycetemcomitans, belonging to the cluster of serotype b strains of A. actinomycetemcomitans and having a number of other characteristics, was found to be strongly associated with aggressive forms of periodontitis, particularly in North Africa. Although several longitudinal studies still point to the bacterial species, A. actinomycetemcomitans as a risk factor of aggressive periodontitis, it is now also widely accepted that the highly leukotoxic JP2 clone of A. actinomycetemcomitans is implicated in rapidly progressing forms of aggressive periodontitis. The JP2 clone strains are highly prevalent in human populations living in Northern and Western parts of Africa. These strains are also prevalent in geographically widespread populations that have originated from the Northwest Africa. Only sporadic signs of a dissemination of the JP2 clone strains to non-African populations have been found despite Africans living geographically widespread for hundreds of years. It remains an unanswered question if a particular host tropism exists as a possible explanation for the frequent colonization of the Northwest African population with the JP2 clone. Two exotoxins of A. actinomycetemcomitans are known, leukotoxin (LtxA) and cytolethal distending toxin (Cdt). LtxA is able to kill human immune cells, and Cdt can block cell cycle progression in eukaryotic cells and thus induce cell cycle arrest. Whereas the leukotoxin production is enhanced in JP2 clone strains thus increasing the virulence potential of A. actinomycetemcomitans, it has not been possible so far to demonstrate such a role for Cdt. Lines of evidence have led to the understanding of the highly leukotoxic JP2 clone of A. actinomycetemcomitans as an aetiological factor of aggressive periodontitis. Patients, who are colonized with the JP2 clone, are likely to share this clone with several family members because the clone is transmitted through close contacts. This is a challenge to the clinicians. The patients need intense monitoring of their periodontal status as the risk for developing severely progressing periodontal lesions are relatively high. Furthermore, timely periodontal treatment, in some cases including periodontal surgery supplemented by the use of antibiotics, is warranted. Preferably, periodontal attachment loss should be prevented by early detection of the JP2 clone of A. actinomycetemcomitans by microbial diagnostic testing and/or by preventive means.

Characterization and serotype distribution of Aggregatibacter actinomycetemcomitans isolated from a population of periodontitis patients in Spain

OBJECTIVE

There is no study characterizing the variability of Aggregatibacter actinomycetemcomitans isolates in periodontitis patients in Spain. It is therefore the aim of this investigation to study the serotype distribution of A. actinomycetemcomitans strains isolated from periodontitis patients in Spain. The polymorphism of the genes that codifies the leukotoxin and the operon of the cytolethal-distending toxin (cdt) will also be investigated.

DESIGN

From a total of 701 patients samples, 40 A. actinomycetemcomitans-positive periodontitis patients were included in the study (mean age 45.3, 62.5% females) and their clinical periodontal status was assessed. On average, 1-3 isolates from each patient were sub-cultured and characterized by PCR.

RESULTS

Using culture the prevalence of A. actinomycetemcomitans was 5.7%. The most frequent serotype was "b", being 30 patients infected by a unique serotype, while 7 patients showed co-colonization, mostly with serotypes "a" and "b". From the 79 pure isolates obtained, 24 were from serotype "a", 30 from serotype "b", 12 from serotype "c" and 4 from serotype "d". Further characterization of these samples showed that none of these 79 isolates demonstrated the 530-bp deletion in the leukotoxin's promoter region that characterizes the JP2 strain. Conversely 65.8% of the isolates were cdt+.

CONCLUSIONS

The most common serotypes were "a" and "b", being serotype "b" the most prevalent in mono-colonization, while serotypes "e" and "f" were not detected. In the majority of samples, operon that codifies the cdt (65.8%) and the genes responsible for the codification of leukotoxin (100%) were found. None of the isolates were JP2 strains.

Quantitative molecular detection of putative periodontal pathogens in clinically healthy and periodontally diseased subjects

Periodontitis is a multi-microbial oral infection with high prevalence among adults. Putative oral pathogens are commonly found in periodontally diseased individuals. However, these organisms can be also detected in the oral cavity of healthy subjects. This leads to the hypothesis, that alterations in the proportion of these organisms relative to the total amount of oral microorganisms, namely their abundance, rather than their simple presence might be important in the transition from health to disease. Therefore, we developed a quantitative molecular method to determine the abundance of various oral microorganisms and the portion of bacterial and archaeal nucleic acid relative to the total nucleic acid extracted from individual samples. We applied quantitative real-time PCRs targeting single-copy genes of periodontal bacteria and 16S-rRNA genes of Bacteria and Archaea. Testing tongue scrapings of 88 matched pairs of periodontally diseased and healthy subjects revealed a significantly higher abundance of P. gingivalis and a higher total bacterial abundance in diseased subjects. In fully adjusted models the risk of being periodontally diseased was significantly higher in subjects with high P. gingivalis and total bacterial abundance. Interestingly, we found that moderate abundances of A. actinomycetemcomitans were associated with reduced risk for periodontal disease compared to subjects with low abundances, whereas for high abundances, this protective effect leveled off. Moderate archaeal abundances were health associated compared to subjects with low abundances. In conclusion, our methodological approach unraveled associations of the oral flora with periodontal disease, which would have gone undetected if only qualitative data had been determined.

Breaking the Gingival Epithelial Barrier: Role of the Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin in Oral Infectious Disease

The Gram-negative bacterium Aggregatibacter actinomycetemcomitans is part of the HACEK group that causes infective endocarditis, a constituent of the oral flora that promotes some forms of periodontal disease and a member of the family of species that secrete a cytolethal distending toxin (Cdt). The family of bacteria that express the cdt genes participate in diseases that involve the disruption of a mucosal or epithelial layer. In vitro studies have shown that human gingival epithelial cells (HGEC) are native targets of the Cdt that typically induces DNA damage that signals growth arrest at the G₂/M interphase of the cell cycle. The gingival epithelium is an early line of defense in the oral cavity against microbial assault. When damaged, bacteria collectively gain entry into the underlying connective tissue where microbial products can affect processes and pathways in infiltrating inflammatory cells culminating in the destruction of the attachment apparatus of the tooth. One approach has been the use of an ex vivo gingival explant model to assess the effects of the Cdt on the morphology and integrity of the tissue. The goal of this review is to provide an overview of these studies and to critically examine the potential contribution of the Cdt to the breakdown of the protective gingival barrier.

Serotypes of Aggregatibacter actinomycetemcomitans in relation to periodontal status and geographic origin of individuals-a review of the literature

Objectives: Several studies have focused on the relationship among serotype distribution, ethnical status and geographic populations, and periodontal conditions. Studies that have investigated the prevalence and the distribution of A. actinomycetemcomitans serotypes and the relation between the different serotypes of the bacterium and periodontal status were reviewed. Material and Methods: A systematic literature search for publications regarding the distribution of A. actinomycetemcomitans serotypes in subgingival samples of periodontitis patients and periodontally healthy subjects by employing polymerase chain reaction (PCR) was conducted. Results: From the 85 studies identified in the first analysis, only 12 met all inclusion and exclusion criteria. Clinical isolates from diverse geographic populations with different periodontal conditions were evaluated. Serotypes a, b and c were largely found, and serotype c was the most prevalent. They were isolated from various periodontal conditions, including aggressive periodontitis. Conclusions: The available literature suggests that serotypes a, b, and c are globally dominant, serotypes d and e are rare, and the prevalence of the most recently identified serotype fis still unknown. It is widely accepted that distribution patterns of A. actinomycetemcomitans vary among subjects of different ethnicity and geographic regions. The correlation of different serotypes with various periodontal conditions remains unclear.

Key words:Aggregatibacter actinomycetemcomitans, serotypes, periodontal disease, prevalence.