Phenotypic and genotypic features of Aggregatibacter actinomycetemcomitans isolated from patients with periodontal disease

Connections between Exoproteome Heterogeneity and Virulence in the Oral Pathogen Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a Gram-negative bacterial pathogen associated with severe periodontitis and nonoral diseases. Clinical isolates of A. actinomycetemcomitans display a rough (R) colony phenotype with strong adherent properties. Upon prolonged culturing, nonadherent strains with a smooth (S) colony phenotype emerge. To date, most virulence studies on A. actinomycetemcomitans have been performed with S strains of A. actinomycetemcomitans, whereas the virulence of clinical R isolates has received relatively little attention. Since the extracellular proteome is the main bacterial reservoir of virulence factors, the present study was aimed at a comparative analysis of this subproteome fraction for a collection of R isolates and derivative S strains, in order to link particular proteins to the virulence of A. actinomycetemcomitans with serotype b. To assess the bacterial virulence, we applied different infection models based on larvae of the greater wax moth Galleria mellonella, a human salivary gland-derived epithelial cell line, and freshly isolated neutrophils from healthy human volunteers. A total number of 351 extracellular A. actinomycetemcomitans proteins was identified by mass spectrometry, with the S strains consistently showing more extracellular proteins than their parental R isolates. A total of 50 known extracellular virulence factors was identified, of which 15 were expressed by all investigated bacteria. Importantly, the comparison of differences in exoproteome composition and virulence highlights critical roles of 10 extracellular proteins in the different infection models. Together, our findings provide novel clues for understanding the virulence of A. actinomycetemcomitans and for development of potential preventive or therapeutic avenues to neutralize this important oral pathogen.

IMPORTANCE Periodontitis is one of the most common inflammatory diseases worldwide, causing high morbidity and decreasing the quality of life of millions of people. The bacterial pathogen Aggregatibacter actinomycetemcomitans is strongly associated with aggressive forms of periodontitis. Moreover, it has been implicated in serious nonoral infections, including endocarditis and brain abscesses. Therefore, it is important to investigate how A. actinomycetemcomitans can cause disease. In the present study, we applied a mass spectrometry approach to make an inventory of the virulence factors secreted by different clinical A. actinomycetemcomitans isolates and derivative strains that emerged upon culturing. We subsequently correlated the secreted virulence factors to the pathogenicity of the investigated bacteria in different infection models. The results show that a limited number of extracellular virulence factors of A. actinomycetemcomitans have central roles in pathogenesis, indicating that they could be druggable targets to prevent or treat oral disease.

Oleoresins and naturally occurring compounds of Copaifera genus as antibacterial and antivirulence agents against periodontal pathogens

Invasion of periodontal tissues by Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans can be associated with aggressive forms of periodontitis. Oleoresins from different copaifera species and their compounds display various pharmacological properties. The present study evaluates the antibacterial and antivirulence activity of oleoresins obtained from different copaifera species and of ten isolated compounds against two causative agents of periodontitis. The following assays were performed: determination of the minimum inhibitory concentration (MIC), determination of the minimum bactericidal concentration (MBC), and determination of the antibiofilm activity by inhibition of biofilm formation and biofilm eradication tests. The antivirulence activity was assessed by hemagglutination, P. gingivalis Arg-X and Lis-X cysteine protease inhibition assay, and A. actinomycetemcomitans leukotoxin inhibition assay. The MIC and MBC of the oleoresins and isolated compounds 1, 2, and 3 ranged from 1.59 to 50 μg/mL against P. gingivalis (ATCC 33277) and clinical isolates and from 6.25 to 400 μg/mL against A. actinomycetemcomitans (ATCC 43717) and clinical isolates. About the antibiofilm activity, the oleoresins and isolated compounds 1, 2, and 3 inhibited biofilm formation by at least 50% and eradicated pre-formed P. gingivalis and A. actinomycetemcomitans biofilms in the monospecies and multispecies modes. A promising activity concerning cysteine protease and leucotoxin inhibition was also evident. In addition, molecular docking analysis was performed. The investigated oleoresins and their compounds may play an important role in the search for novel sources of agents that can act against periodontal pathogens.

Expression of IL-10 in A.actinomycetemcomitans Induced Rat Treated by Purple Miana Leaves

Periodontitis therapy originating from local natural resources is still lacking so it needs to be researched and developed, one of the natural resources from Soppeng Regency in South Sulawesi, Indonesia is the purple miana leaf. It has not been reported before about the effect of purple miana leaf extract on periodontitis related to IL-10 mRNA expression. This study aims to determine the effect of purple miana leaf extract on IL-10 mRNA expression in rat induced by Aggregatibacter actinomycetemcomitans. Rats were divided into three groups, purple miana leaf extract (PMLE), negative control (aquades), antibiotic (levofloxacin nine mg/kg body weight) as positive control. Rat blood was drawn before (H1) and after induction of 3x108 cfu/ml Aggregatibacter actinomycetemcomitans in the gingival sulcus of the mandibular anterior teeth/after periodontitis (H8) and seven days after intervention (H15). IL 10 mRNA expression was measured by Real-time PCR. The results obtained are processed using SPSS. There were no significant differences in H1-H8 in all groups. IL-10 mRNA expression on H8-H15 has a different pattern between PMLE, negative control and positive control. In the negative control, there was a decrease in IL-10 mRNA expression in H8-H15. In PMLE and positive control, an increase in IL-10 mRNA expression. The treatment of purple miana leaf extract in rat induced with Aggregatibacter actinomycetemcomitans significantly had the same effect as levofloxacin on IL-10 mRNA expression.

Qualitative, quantitative and genotypic evaluation of Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum isolated from individuals with different periodontal clinical conditions

Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum are strongly associated with periodontitis, and their evaluations are relevant to understand their role in the etiology and progression of periodontal diseases. In this study, the qualitative and quantitative detection of A. actinomycetemcomitans and F. nucleatum, as well as their genetic diversity, were evaluated in individuals with gingivitis, chronic periodontitis and periodontally healthy. In addition, the biotyping, serotyping, and prevalence of the ltx and cdt genes in A. actinomycetemcomitans were also determined. Subgingival biofilms obtained from gingivitis (70), periodontitis (75) and healthy (95) individuals were analyzed by cultures and PCR. Bacterial typing and presence of ltx and cdt genes in A. actinomycetemcomitans were also verified. DNA from A. actinomycetemcomitans and F. nucleatum was detected respectively, in 65.7% and 57.1% of gingivitis, 80% and 68% of periodontitis, and 57.8% and 37.8% of healthy. A. actinomycetemcomitans from gingivitis were biotypes I, II, IV, V, and X, and serotypes a, c, and e. In periodontitis, biotypes II, VI, and X, and serotypes a, b, and c were found. In healthy subjects, biotypes II and X, and serotypes b and c were found. The LTX and ltxA were observed in strains from gingivitis and periodontitis pockets. Subsequently, our data also showed no direct relationship between ltxA gene expression and leukotoxin gene 530-bp presence. On the other hand, cdt gene predominated during the inflammatory disease process. Our results strongly support a role of A. actinomycetemcomitans and F. nucleatum in advanced stage of periodontal disease.

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.

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.

Leukotoxicity of Aggregatibacter actinomycetemcomitans in generalized aggressive periodontitis in Brazilians and their family members

OBJECTIVE

The purpose of this study was to examine the leukotoxin promoter types of Aggregatibacter actinomycetemcomitans clones in subjects with generalized aggressive periodontitis (GAgP) and in their family members (FM).

MATERIAL AND METHODS

Thirty-five patients with GAgP (33.9±7.1 years), 33 of their FM (22.8±11.4 years), and 41 patients with chronic periodontitis (CP) (44.1±9.4 years) were clinically analyzed using the plaque index, gingival index, probing depth (PD), and clinical attachment level (CAL). Subgingival biofilm samples were collected from four interproximal periodontal sites (>PD and >CAL) of each patient. The presence of A. actinomycetemcomitans and its leukotoxic clone was confirmed by polymerase chain reaction (PCR).

RESULTS

A. actinomycetemcomitans was observed in 23 (51.1%) GAgP patients and 16 (30.1%) CP patients. Thirty-seven (94.8%) patients showed minimally leukotoxic strains and 2 (5.1%) showed highly leukotoxic strains. In the FM group, 10 (30.3%) had aggressive periodontitis (AgP), 12 (36.3%) had CP, 11 (33.3%) were periodontally healthy or had gingivitis, and 12.2% were A. actinomycetemcomitans positive. Greater full mouth PD and CAL were observed in GAgP patients positive for the bacteria than those negative for it (p<;0.05), and the presence of A. actinomycetemcomitans positively correlated with GAgP (Odds ratio, 3.1; confidence interval, 1.4-7.0; p=0.009).

CONCLUSIONS

The presence of A. actinomycetemcomitans was associated with the clinical condition of GAgP, with most patients exhibiting a generalized form of the disease and minimally leukotoxic clones. Most of the relatives of GAgP patients presented either CP or AgP.

Progression of attachment loss is strongly associated with presence of the JP2 genotype of Aggregatibacter actinomycetemcomitans: a prospective cohort study of a young adolescent population

AIM

To assess the progression of attachment loss (AL) during a 2-year period according to the presence of JP2 and non-JP2 genotypes of Aggregatibacter actinomycetemcomitans in a Ghanaian adolescent population.

METHODS

A total of 500 adolescents (mean age 13.2 years, SD ± 1.5) were enrolled in the study. After 2 years, 397 (79.4%) returned for a periodontal re-examination, including the measurement of AL. The carrier status of the JP2 and non-JP2 genotypes of A. actinomycetemcomitans was evaluated in a baseline examination 2 years earlier.

RESULTS

Individuals who carried the JP2 genotype of A. actinomycetemcomitans had a significantly increased risk [relative risk (RR) = 7.3] of developing AL ≥ 3 mm. The mean AL at the follow-up and the mean 2-year progression of AL were significantly higher in the JP2 genotype-positive group (n = 38) compared with the group positive for the non-JP2 genotypes of A. actinomycetemcomitans (n = 169), and the group of A. actinomycetemcomitans-negative individuals (n = 190). The JP2 genotype was strongly associated with the progression of AL ≥ 3 mm (OR = 14.3). The non-JP2 genotypes of A. actinomycetemcomitans were also, however, less pronounced, associated with the progression of AL ≥ 3 mm (OR = 3.4).

CONCLUSION

The JP2 genotype of A. actinomycetemcomitans is strongly associated with the progression of AL.