Characterization of the O-polysaccharide structure of lipopolysaccharide from Actinobacillus actinomycetemcomitans serotype b

Engineering Planar Gram-Negative Outer Membrane Mimics Using Bacterial Outer Membrane Vesicles

Antibiotic resistance is a major challenge in modern medicine. The unique double membrane structure of gram-negative bacteria limits the efficacy of many existing antibiotics and adds complexity to antibiotic development by limiting transport of antibiotics to the bacterial cytosol. New methods to mimic this barrier would enable high-throughput studies for antibiotic development. In this study, we introduce an innovative approach to modify outer membrane vesicles (OMVs) from Aggregatibacter actinomycetemcomitans, to generate planar supported lipid bilayer membranes. Our method first involves the incorporation of synthetic lipids into OMVs using a rapid freeze-thaw technique to form outer membrane hybrid vesicles (OM-Hybrids). Subsequently, these OM-Hybrids can spontaneously rupture when in contact with SiO2 surfaces to form a planar outer membrane supported bilayer (OM-SB). We assessed the formation of OM-Hybrids using dynamic light scattering and a fluorescence quenching assay. To analyze the formation of OM-SBs from OM-Hybrids we used quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence recovery after photobleaching (FRAP). Additionally, we conducted assays to detect surface-associated DNA and proteins on OM-SBs. The interaction of an antimicrobial peptide, polymyxin B, with the OM-SBs was also assessed. These findings emphasize the capability of our platform to produce planar surfaces of bacterial outer membranes, which in turn, could function as a valuable tool for streamlining the development of antibiotics.

Chemical synthesis of the O-antigen repeating unit of Actinobacillus actinomycetemcomitans serotype f

Herein, we report the total synthesis of the trisaccharide repeating unit of the O-antigen of Actinobacillus actinomycetemcomitans serotype f. The trisaccharide comprising of α-(1-2) and α-(1-3)-linked L-rhamnopyranosides backbone with the latter rhamnose containing a branching N-acetyl-d-galactosaminopyranoside at the C2-O via a β-glycosidic bond was synthesized by two methods. Initially, the protected trisaccharide has been synthesized by step-wise assembly of the monosaccharide building blocks and subsequently the former was synthesized by the one-pot assembly of the latter components. The synthesized trisaccharide contains an aminoethyl linker appended as an O-glycoside at the reducing end, thereby providing scope for further conjugation for different applications.

Human Serum Mediated Bacteriophage Life Cycle Switch in Aggregatibacter actinomycetemcomitans Is Linked to Pyruvate Dehydrogenase Complex

Antimicrobial resistance is rising as a major global public health threat and antibiotic resistance genes are widely spread among species, including human oral pathogens, e.g., Aggregatibacter actinomycetemcomitans. This Gram-negative, capnophilic, facultative anaerobe is well recognized as a causative agent leading to periodontal diseases, as well as seriously systemic infections including endocarditis. A. actinomycetemcomitans has also evolved mechanisms against complement-mediated phagocytosis and resiliently survives in serum-rich in vivo environments, i.e., inflamed periodontal pockets and blood circulations. This bacterium, however, demonstrated increasing sensitivity to human serum, when being infected by a pseudolysogenic bacteriophage S1249, which switched to the lytic state as a response to human serum. Concomitantly, the pyruvate dehydrogenase complex (PDHc), which is composed of multiple copies of three enzymes (E1, E2, and E3) and oxidatively decarboxylates pyruvate to acetyl-CoA available for tricarboxylic acid (TCA) cycle, was found up-regulated 10-fold in the bacterial lysogen after human serum exposure. The data clearly indicated that certain human serum components induced phage virion replication and egress, resulting in bacterial lysis. Phage manipulation of bacterial ATP production through regulation of PDHc, a gatekeeper linking glycolysis to TCA cycle through aerobic respiration, suggests that a more efficient energy production and delivery system is required for phage progeny replication and release in this in vivo environment. Insights into bacteriophage regulation of bacterial fitness in a mimic in vivo condition will provide alternative strategies to control bacterial infection, in addition to antibiotics.

Genomic Islands Shape the Genetic Background of Both JP2 and Non-JP2 Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a periodontal pathogen associated with periodontitis. This species exhibits substantial variations in gene content among different isolates and has different virulence potentials. This study examined the distribution of genomic islands and their insert sites among genetically diverse A. actinomycetemcomitans strains by comparative genomic analysis. The results showed that some islands, presumably more ancient, were found across all genetic clades of A. actinomycetemcomitans. In contrast, other islands were specific to individual clades or a subset of clades and may have been acquired more recently. The islands for the biogenesis of serotype-specific antigens comprise distinct genes located in different loci for serotype a and serotype b–f strains. Islands that encode the same cytolethal distending toxins appear to have been acquired via distinct mechanisms in different loci for clade b/c and for clade a/d/e/f strains. The functions of numerous other islands remain to be elucidated. JP2 strains represent a small branch within clade b, one of the five major genetic clades of A. actinomycetemcomitans. In conclusion, the complex process of genomic island acquisition, deletion, and modification is a significant force in the genetic divergence of A. actinomycetemcomitans. Assessing the genetic distinctions between JP2 and non-JP2 strains must consider the landscape of genetic variations shaped by evolution.

The serotype a-EmaA adhesin of Aggregatibacter actinomycetemcomitans does not require O-PS synthesis for collagen binding activity

Aggregatibacter actinomycetemcomitans, a causative agent of periodontitis and non-oral diseases, synthesizes a trimeric extracellular matrix protein adhesin A (EmaA) that mediates collagen binding and biofilm formation. EmaA is found as two molecular forms, which correlate with the serotype of the bacterium. The canonical protein (b-EmaA), associated with serotypes b and c, has a monomeric molecular mass of 202 kDa. The collagen binding activity of b-EmaA is dependent on the presence of O-polysaccharide (O-PS), whereas biofilm activity is independent of O-PS synthesis. The EmaA associated with serotype a strains (a-EmaA) has a monomeric molecular mass of 173 kDa and differs in the amino acid sequence of the functional domain of the protein. In this study, a-emaA was confirmed to encode a protein that forms antenna-like appendages on the surface of the bacterium, which were found to be important for both collagen binding and biofilm formation. In an O-PS-deficient talose biosynthetic (tld) mutant strain, the electrophoretic mobility of the a-EmaA monomers was altered and the amount of membrane-associated EmaA was decreased when compared to the parent strain. The mass of biofilm formed remained unchanged. Interestingly, the collagen binding activity of the mutant strain was similar to the activity associated with the parent strain, which differs from that observed with the canonical b-EmaA isoform. These data suggest that the properties of the a-EmaA isoform are like those of b-EmaA, with the exception that collagen binding activity is independent of the presence or absence of the O-PS.

O-Polysaccharide Plays a Major Role on the Virulence and Immunostimulatory Potential of Aggregatibacter actinomycetemcomitans During Periodontal Infection

Aggregatibacter actinomycetemcomitans is a Gram-negative oral bacterium with high immunostimulatory and pathogenic potential involved in the onset and progression of periodontitis, a chronic disease characterized by aberrant immune responses followed by tooth-supporting bone resorption, which eventually leads to tooth loss. While several studies have provided evidence related to the virulence factors of A. actinomycetemcomitans involved in the host cell death and immune evasion, such as its most studied primate-specific virulence factor, leukotoxin, the role of specific lipopolysaccharide (LPS) domains remain poorly understood. Here, we analyzed the role of the immunodominant domain of the LPS of A. actinomycetemcomitans termed O-polysaccharide (O-PS), which differentiates the distinct bacterial serotypes based on its antigenicity. To determine the role of the O-PS in the immunogenicity and virulence of A. actinomycetemcomitans during periodontitis, we analyzed the in vivo and in vitro effect of an O-PS-defective transposon mutant serotype b strain, characterized by the deletion of the rmlC gene encoding the α-L-rhamnose sugar biosynthetic enzyme. Induction of experimental periodontitis using the O-PS-defective rmlC mutant strain resulted in lower tooth-supporting bone resorption, infiltration of Th1, Th17, and Th22 lymphocytes, and expression of Ahr, Il1b, Il17, Il23, Tlr4, and RANKL (Tnfsf11) in the periodontal lesions as compared with the wild-type A. actinomycetemcomitans strain. In addition, the O-PS-defective rmlC mutant strain led to impaired activation of antigen-presenting cells, with less expression of the co-stimulatory molecules CD40 and CD80 in B lymphocytes and dendritic cells, and downregulated expression of Tnfa and Il1b in splenocytes. In conclusion, these data demonstrate that the O-PS from the serotype b of A. actinomycetemcomitans plays a key role in the capacity of the bacterium to prime oral innate and adaptive immune responses, by triggering the Th1 and Th17-driven tooth-supporting bone resorption during periodontitis.

Inhibitory effect of serotype a of Aggregatibacter actinomycetemcomitans on the increased destructive potential of serotype b

OBJECTIVE

The serotype b of Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) induces higher cytokine production in dendritic cells (DCs) compared with the other serotypes. However, this increased immunostimulatory potential was modified when DCs were co-infected with the other A. actinomycetemcomitans serotypes. This study aimed to analyze whether the production of interferon gamma (IFN-γ), C-reactive protein (CRP), matrix metalloproteinase (MMP)-2, and MMP-9, as well as the activity of osteoclasts, also varies when DCs are co-infected with the A. actinomycetemcomitans serotypes.

MATERIALS AND METHODS

Human DCs were stimulated with the A. actinomycetemcomitans serotypes using the following stimulatory conditions: serotype a/b/c/a+b/a+c/b+c/a+b+c. The IFN-γ, CRP, and MMP-2 levels were quantified by ELISA. The active form of MMP-9 was quantified using fluorescent functional assays. The MMP-2 gelatinolytic activity was identified by zymogram. The osteoclast activity was determined by quantifying the TRAP expression and resorption-pit formation using cytochemistry and osteoassays.

RESULTS

Higher levels of IFN-γ, CRP, MMP-2, MMP-9, and osteoclast activity were detected when DCs were stimulated with the serotype b of A. actinomycetemcomitans compared with the others. This increased immunostimulatory potential attributed to serotype b diminished when DCs were co-infected with the serotype a.

CONCLUSIONS

This study provides new insights into the virulence of A. actinomycetemcomitans and reveals important differences in the immunostimulatory and pro-destructive potential among its serotypes.

Virulence and Pathogenicity Properties of Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a periodontal pathogen colonizing the oral cavity of a large proportion of the human population. It is equipped with several potent virulence factors that can cause cell death and induce or evade inflammation. Because of the large genetic diversity within the species, both harmless and highly virulent genotypes of the bacterium have emerged. The oral condition and age, as well as the geographic origin of the individual, influence the risk to be colonized by a virulent genotype of the bacterium. In the present review, the virulence and pathogenicity properties of A. actinomycetemcomitans will be addressed.

Serotype b of Aggregatibacter actinomycetemcomitans triggers pro-inflammatory responses and amyloid beta secretion in hippocampal cells: a novel link between periodontitis and Alzheimer´s disease?

Introduction: Previous reports have proposed that Periodontal disease (PDis) predisposes to Alzheimer's disease (AD), both highly prevalent pathologies among the elderly. The bacteria Aggregatibacter actinomycetemcomitans (Aa), associated with the most aggressive forms of PDis, are classified in different serotypes with distinct virulence according to the antigenicity of their lipopolysaccharide (LPS). Methods: Here, we determined the effects of purified LPS, from serotypes a, b or c of Aa, on primary cultures of microglia or mixed hippocampal cells. Results: We found that both culture types exhibited higher levels of inflammatory cytokines (IL-1β, IL-6 and TNFα) when treated with serotype b-LPS, compared with controls, as quantified by qPCR and/or ELISA. Also, cultures treated with serotype a-LPS displayed increased mRNA levels of the modulatory cytokines IL-4 and IL-10. Mixed hippocampal cultures treated with serotype b-LPS exhibited severe neuronal morphological changes and displayed increased levels of secreted Aβ_1-42 peptide. These results indicate that LPS from different Aa serotypes triggers discriminatory immune responses, which differentially affect primary hippocampal cells. Conclusion: Altogether, our results show that treatment with serotype b-LPS triggers the secretion of proinflammatory cytokines by microglia, induces neurite shrinking, and increases the extracellular Aβ1-42 levels, all features strongly associated with the etiology of AD.

A Nonfimbrial Adhesin of Aggregatibacter actinomycetemcomitans Mediates Biofilm Biogenesis

Periodontitis is an inflammatory disease caused by polymicrobial biofilms. The periodontal pathogen Aggregatibacter actinomycetemcomitans displays two proteinaceous surface structures, the fimbriae and the nonfimbrial extracellular matrix binding protein A (EmaA), as observed by electron microscopy. Fimbriae participate in biofilm biogenesis and the EmaA adhesins mediate collagen binding. However, in the absence of fimbriae, A. actinomycetemcomitans still retains the potential to form robust biofilms, suggesting that other surface macromolecules participate in biofilm development. Here, isogenic mutant strains lacking EmaA structures, but still expressing fimbriae, were observed to have reduced biofilm potential. In strains lacking both EmaA and fimbriae, biofilm mass was reduced by 80%. EmaA enhanced biofilm formation in different strains, independent of the fimbriation state or serotype. Confocal microscopy revealed differences in cell density within microcolonies between the EmaA positive and mutant strains. EmaA-mediated biofilm formation was found to be independent of the glycosylation state and the precise three-dimensional conformation of the protein, and thus this function is uncorrelated with collagen binding activity. The data suggest that EmaA is a multifunctional adhesin that utilizes different mechanisms to enhance bacterial binding to collagen and to enhance biofilm formation, both of which are important for A. actinomycetemcomitans colonization and subsequent infection.

Characterization and production of multifunctional cationic peptides derived from rice proteins

Food proteins have been identified as a source of bioactive peptides. These peptides are inactive within the sequence of the parent protein and must be released during gastrointestinal digestion, fermentation, or food processing. Of bioactive peptides, multifunctional cationic peptides are more useful than other peptides that have specific activity in promotion of health and/or the treatment of diseases. We have identified and characterized cationic peptides from rice enzymes and proteins that possess multiple functions, including antimicrobial, endotoxin-neutralizing, arginine gingipain-inhibitory, and/or angiogenic activities. In particular, we have elucidated the contribution of cationic amino acids (arginine and lysine) in the peptides to their bioactivities. Further, we have discussed the critical parameters, particularly proteinase preparations and fractionation or purification, in the enzymatic hydrolysis process for producing bioactive peptides from food proteins. Using an ampholyte-free isoelectric focusing (autofocusing) technique as a tool for fractionation, we successfully prepared fractions containing cationic peptides with multiple functions.

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.

Identification of genes involved in biosynthesis of Actinobacillus pleuropneumoniae serotype 1 O-antigen and biological properties of rough mutants

Actinobacillus pleuropneumoniae is an important pathogen of swine. Lipopolysaccharide (LPS) has been identified as the major adhesin of A. pleuropneumoniae and it is involved in adherence to porcine respiratory tract cells. We previously generated seven rough LPS mutants of A. pleuropneumoniae serotype 1 by using a mini-Tn 10 transposon mutagenesis system [Rioux S, Galarneau C, Harel J et al. Isolation and characterization of mini-Tn 10 lipopolysaccharide mutants of Actinobacillus pleuropneumoniae serotype 1. Can J Microbiol 1999; 45: 1017—1026]. The purpose of the present study was to characterize these mutants in order to learn more about LPS O-antigen biosynthesis genes and their organization in A. pleuropneumoniae, and to determine the surface properties and virulence in pigs of these isogenic mutants. By mini-Tn 10 insertions in rough mutants, four putative genes (ORF12, ORF16, ORF17, and ORF18) involved in O-antigen biosynthesis in A. pleuropneumoniae serotype 1 were found within a region of 18 ORFs. This region is homologous to the gene cluster of serotype-specific O-polysaccharide biosynthesis from A. actinomycetemcomitans strain Y4 (serotype b). Two mutants showed homology to a protein with identity to glycosyltransferases (ORF12); two others had the mini-Tn 10 insertion localized in genes encoding for two distinct proteins with identity to rhamnosyltransferases (ORF16 and ORF17) and three showed homology to a protein which is known to initiate polysaccharide synthesis (ORF18). These four ORFs were also present in A. pleuropneumoniae serotypes 9 and 11 that express an O-antigen that serologically cross-reacts with serotype 1. Evaluation of some biological properties of rough mutants seems to indicate that the absence of O-chains does not appear to have an influence on the virulence of the bacteria in pigs and on the overall surface hydrophobicity, charge and hemoglobin-binding activity, or on LAL activation. An acapsular mutant was included in the present study in order to compare the influence of O-chains and capsule polysaccharides on different cell surface properties. Our data suggest that capsular polysaccharides and not O-chains polysaccharides have a major influence on surface properties of A. pleuropneumoniae serotype 1 and its virulence in pigs.

Human Serum-Specific Activation of Alternative Sigma Factors, the Stress Responders in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans, a known pathogen causing periodontal disease and infective endocarditis, is a survivor in the periodontal pocket and blood stream; both environments contain serum as a nutrient source. To screen for unknown virulence factors associated with this microorganism, A. actinomycetemcomitans was grown in serum-based media to simulate its in vivo environment. Different strains of A. actinomycetemcomitans showed distinct growth phenotypes only in the presence of human serum, and they were grouped into high- and low-responder groups. High-responders comprised mainly serotype c strains, and showed an unusual growth phenomenon, featuring a second, rapid increase in turbidity after 9-h incubation that reached a final optical density 2- to 7-fold higher than low-responders. Upon further investigation, the second increase in turbidity was not caused by cell multiplication, but by cell death. Whole transcriptomic analysis via RNA-seq identified 35 genes that were up-regulated by human serum, but not horse serum, in high-responders but not in low-responders, including prominently an alternative sigma factor rpoE (σ^E). A lacZ reporter construct driven by the 132-bp rpoE promoter sequence of A. actinomycetemcomitans responded dramatically to human serum within 90 min of incubation only when the construct was carried by a high responder strain. The rpoE promoter is 100% identical among high- and low-responder strains. Proteomic investigation showed potential interactions between human serum protein, e.g. apolipoprotein A1 (ApoA1) and A. actinomycetemcomitans. The data clearly indicated a different activation process for rpoE in high- versus low-responder strains. This differential human serum-specific activation of rpoE, a putative extra-cytoplasmic stress responder and global regulator, suggests distinct in vivo adaptations among different strains of A. actinomycetemcomitans.

Variability of the dendritic cell response triggered by different serotypes of Aggregatibacter actinomycetemcomitans or Porphyromonas gingivalis is toll-like receptor 2 (TLR2) or TLR4 dependent

BACKGROUND

Different serotypes of Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis have been shown to induce differential dendritic cell (DC) responses. This study investigates whether cytokine and CC-chemokine receptor (CCR) production by DCs stimulated with different serotypes of A. actinomycetemcomitans or P. gingivalis is Toll-like receptor 2 (TLR2) and/or TLR4 dependent.

METHODS

DCs were obtained from healthy individuals and primed at a multiplicity of infection (MOI) of 10(2) with different A. actinomycetemcomitans or P. gingivalis serotypes in the presence or absence of anti-TLR2 or anti-TLR4 blocking antibodies. TLR2 and TLR4 expression, CCR5 and CCR6 expression, and interleukin (IL)-1β, IL-10, IL-12, and IL-23 expression and secretion were quantified by flow cytometry, real-time reverse-transcription polymerase chain reaction, and enzyme-linked immunosorbent assay.

RESULTS

When DCs were stimulated with serotype b of A. actinomycetemcomitans or serotype K1 of P. gingivalis, higher levels of TLR2 or TLR4, respectively, were detected compared to DCs stimulated with the other serotypes. Similarly, higher levels of cytokines and CCRs were detected in serotype b- or serotype K1-primed DCs compared to the others, and these increased levels positively correlated with levels of TLR2 or TLR4. When TLR2 signaling was blocked using a specific anti-TLR2 monoclonal antibody, serotype b-induced cytokine and CCR expression was inhibited; when TLR4 signaling was blocked, serotype K1-induced response was inhibited.

CONCLUSIONS

These results demonstrate that the variability of secretion of cytokines and expression of CCRs detected in DCs stimulated with different serotypes of A. actinomycetemcomitans or P. gingivalis is TLR2 or TLR4 dependent, respectively.

Differential expression of CC chemokines (CCLs) and receptors (CCRs) by human T lymphocytes in response to different Aggregatibacter actinomycetemcomitans serotypes

In Aggregatibacter actinomycetemcomitans, different serotypes have been described based on LPS antigenicity. Recently, our research group has reported a differential immunogenicity when T lymphocytes were stimulated with these different serotypes. In particular, it was demonstrated that the serotype b of A. actinomycetemcomitans has a stronger capacity to trigger Th1- and Th17-type cytokine production.

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.

Classification, identification, and clinical significance of Haemophilus and Aggregatibacter species with host specificity for humans

The aim of this review is to provide a comprehensive update on the current classification and identification of Haemophilus and Aggregatibacter species with exclusive or predominant host specificity for humans. Haemophilus influenzae and some of the other Haemophilus species are commonly encountered in the clinical microbiology laboratory and demonstrate a wide range of pathogenicity, from life-threatening invasive disease to respiratory infections to a nonpathogenic, commensal lifestyle. New species of Haemophilus have been described (Haemophilus pittmaniae and Haemophilus sputorum), and the new genus Aggregatibacter was created to accommodate some former Haemophilus and Actinobacillus species (Aggregatibacter aphrophilus, Aggregatibacter segnis, and Aggregatibacter actinomycetemcomitans). Aggregatibacter species are now a dominant etiology of infective endocarditis caused by fastidious organisms (HACEK endocarditis), and A. aphrophilus has emerged as an important cause of brain abscesses. Correct identification of Haemophilus and Aggregatibacter species based on phenotypic characterization can be challenging. It has become clear that 15 to 20% of presumptive H. influenzae isolates from the respiratory tracts of healthy individuals do not belong to this species but represent nonhemolytic variants of Haemophilus haemolyticus. Due to the limited pathogenicity of H. haemolyticus, the proportion of misidentified strains may be lower in clinical samples, but even among invasive strains, a misidentification rate of 0.5 to 2% can be found. Several methods have been investigated for differentiation of H. influenzae from its less pathogenic relatives, but a simple method for reliable discrimination is not available. With the implementation of identification by matrix-assisted laser desorption ionization-time of flight mass spectrometry, the more rarely encountered species of Haemophilus and Aggregatibacter will increasingly be identified in clinical microbiology practice. However, identification of some strains will still be problematic, necessitating DNA sequencing of multiple housekeeping gene fragments or full-length 16S rRNA genes.

A gene cluster for the synthesis of serotype g-specific polysaccharide antigen in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is an important pathogen related to aggressively progressive periodontal breakdown in adolescents and adults. The species can be divided into six serotypes (a-f) according to their surface carbohydrate antigens. Recently, a new serotype g of A. actinomycetemcomitans was proposed. The aim of the present study was to sequence the gene cluster associated with the biosynthesis of the serotype g-specific polysaccharide antigen and develop serotype-specific primers for PCR assay to identify serotype g strains of A. actinomycetemcomitans. The serotype-specific polysaccharide (SSPS) gene cluster of the NUM-Aa 4039 strain contained 21 genes in 21,842-bp nucleotides. The similarity of the SSPS gene cluster sequence was 96.7 % compared with that of the serotype e strain. Seventeen serotype g genes showed more than 90 % homology both in nucleotide and amino acids to the serotype e strain. Three additional genes with 1,579 bp in NUM-Aa 4039 were inserted into the corresponding ORF13 of the serotype e strain. The serotype g-specific primers were designed from the insertion region of NUM-Aa 4039. Serotypes of the a-f strains were not amplified by serotype-specific g primers; only NUM-Aa 4039 showed an amplicon band. The NUM-Aa 4039 strain was three genes in the SSPS gene cluster different from those of serotype e strain. The specific primers derived from these different regions are useful for identification and distribution of serotype g strain among A. actinomycetemcomitans from clinical samples.

Synthesis of lipopolysaccharide O-antigens by ABC transporter-dependent pathways

The O-polysaccharide (O-PS; O-antigen) of bacterial lipopolysaccharides is made up of repeating units of one or more sugar residues and displays remarkable structural diversity. Despite the structural variations, there are only three strategies for O-PS assembly. The ATP-binding cassette (ABC)-transporter-dependent mechanism of O-PS biosynthesis is widespread. The Escherichia coli O9a and Klebsiella pneumoniae O2a antigens provide prototypes, which are distinguished by the fine details that link glycan polymerization and chain termination at the cytoplasmic face of the inner membrane to its export via the ABC transporter. Here, we describe the current understanding of these processes. Since glycoconjugate assembly complexes that utilize an ABC transporter-dependent pathway are widespread among the bacterial kingdom, the models described here are expected to extend beyond O-PS biosynthesis systems.

Lipopolysaccharides mediate leukotoxin secretion in Aggregatibacter actinomycetemcomitans

We previously reported that lipopolysaccharide (LPS) -related sugars are associated with the glycosylation of the collagen adhesin EmaA, a virulence determinant of Aggregatibacter actinomycetemcomitans. In this study, the role of LPS in the secretion of other virulence factors was investigated. The secretion of the epithelial adhesin Aae, the immunoglobulin Fc receptor Omp34 and leukotoxin were examined in a mutant strain with inactivated TDP-4-keto-6-deoxy-d-glucose 3,5-epimerase (rmlC), which resulted in altered O-antigen polysaccharides (O-PS) of LPS. The secretion of Aae and Omp34 was not affected. However, the leukotoxin secretion, which is mediated by the TolC-dependent type I secretion system, was altered in the rmlC mutant. The amount of secreted leukotoxin in the bacterial growth medium was reduced nine-fold, with a concurrent four-fold increase of the membrane-bound toxin in the mutant compared with the wild-type strain. The altered leukotoxin secretion pattern was restored to the wild-type by complementation of the rmlC gene in trans. Examination of the ltxA mRNA levels indicated that the leukotoxin secretion was post-transcriptionally regulated in the modified O-PS containing strain. The mutant strain also showed increased resistance to vancomycin, an antibiotic dependent on TolC for internalization, indicating that TolC was affected. Overexpression of TolC in the rmlC mutant resulted in an increased TolC level in the outer membrane but did not restore the leukotoxin secretion profile to the wild-type phenotype. The data suggest that O-PS mediate leukotoxin secretion in A. actinomycetemcomitans.

ABC transporters involved in export of cell surface glycoconjugates

Complex glycoconjugates play critical roles in the biology of microorganisms. Despite the remarkable diversity in glycan structures and the bacteria that produce them, conserved themes are evident in the biosynthesis-export pathways. One of the primary pathways involves representatives of the ATP-binding cassette (ABC) transporter superfamily. These proteins are responsible for the export of a wide variety of cell surface oligo- and polysaccharides in both Gram-positive and Gram-negative bacteria. Recent investigations of the structure and function of ABC transporters involved in the export of lipopolysaccharide O antigens have revealed two fundamentally different strategies for coupling glycan polymerization to export. These mechanisms are distinguished by the presence (or absence) of characteristic nonreducing terminal modifications on the export substrates, which serve as chain termination and/or export signals, and by the presence (or absence) of a discrete substrate-binding domain in the nucleotide-binding domain polypeptide of the ABC transporter. A bioinformatic survey examining ABC exporters from known oligo- and polysaccharide biosynthesis loci identifies conserved nucleotide-binding domain protein families that correlate well with themes in the structures and assembly of glycans. The familial relationships among the ABC exporters generate hypotheses concerning the biosynthesis of structurally diverse oligo- and polysaccharides, which play important roles in the biology of bacteria with different lifestyles.

A genomic perspective on the potential of Actinobacillus succinogenes for industrial succinate production

BACKGROUND

Succinate is produced petrochemically from maleic anhydride to satisfy a small specialty chemical market. If succinate could be produced fermentatively at a price competitive with that of maleic anhydride, though, it could replace maleic anhydride as the precursor of many bulk chemicals, transforming a multi-billion dollar petrochemical market into one based on renewable resources. Actinobacillus succinogenes naturally converts sugars and CO2 into high concentrations of succinic acid as part of a mixed-acid fermentation. Efforts are ongoing to maximize carbon flux to succinate to achieve an industrial process.

RESULTS

Described here is the 2.3 Mb A. succinogenes genome sequence with emphasis on A. succinogenes's potential for genetic engineering, its metabolic attributes and capabilities, and its lack of pathogenicity. The genome sequence contains 1,690 DNA uptake signal sequence repeats and a nearly complete set of natural competence proteins, suggesting that A. succinogenes is capable of natural transformation. A. succinogenes lacks a complete tricarboxylic acid cycle as well as a glyoxylate pathway, and it appears to be able to transport and degrade about twenty different carbohydrates. The genomes of A. succinogenes and its closest known relative, Mannheimia succiniciproducens, were compared for the presence of known Pasteurellaceae virulence factors. Both species appear to lack the virulence traits of toxin production, sialic acid and choline incorporation into lipopolysaccharide, and utilization of hemoglobin and transferrin as iron sources. Perspectives are also given on the conservation of A. succinogenes genomic features in other sequenced Pasteurellaceae.

CONCLUSIONS

Both A. succinogenes and M. succiniciproducens genome sequences lack many of the virulence genes used by their pathogenic Pasteurellaceae relatives. The lack of pathogenicity of these two succinogens is an exciting prospect, because comparisons with pathogenic Pasteurellaceae could lead to a better understanding of Pasteurellaceae virulence. The fact that the A. succinogenes genome encodes uptake and degradation pathways for a variety of carbohydrates reflects the variety of carbohydrate substrates available in the rumen, A. succinogenes's natural habitat. It also suggests that many different carbon sources can be used as feedstock for succinate production by A. succinogenes.

Antibody to receptor activator of NF-κB ligand ameliorates T cell-mediated periodontal bone resorption

Activated T and B lymphocytes in periodontal disease lesions express receptor activator of NF-κB ligand (RANKL), which induces osteoclastic bone resorption. The objective of this study was to evaluate the effects of anti-RANKL antibody on periodontal bone resorption in vitro and in vivo. Aggregatibacter actinomycetemcomitans outer membrane protein 29 (Omp29) and A. actinomycetemcomitans lipopolysaccharide (LPS) were injected into 3 palatal gingival sites, and Omp29-specific T clone cells were transferred into the tail veins of rats. Rabbit anti-RANKL IgG antibody or F(ab')₂ antibody fragments thereof were injected into the palatal sites in each rat (days -1, 1, and 3). Anti-RANKL IgG antibody significantly inhibited soluble RANKL (sRANKL)-induced osteoclastogenesis in vitro, in a dose-dependent manner, but also gave rise to a rat antibody response to rabbit IgG in vivo, with no significant inhibition of periodontal bone resorption detected. Lower doses (1.5 and 0.15 μg/3 sites) of F(ab')₂ antibody were not immunogenic in the context of the experimental model. Periodontal bone resorption was inhibited significantly by injection of the anti-RANKL F(ab')₂ antibody into gingivae. The sRANKL concentrations for the antibody-treated groups were decreased significantly compared to those for the untreated group. Osteoclasts on the alveolar bone surface were also diminished significantly after antibody injection. Gingival sRANKL concentration and bone loss showed a significant correlation with one another in animals receiving anti-RANKL F(ab')₂ antibody. These results suggest that antibody to RANKL can inhibit A. actinomycetemcomitans-specific T cell-induced periodontal bone resorption by blockade and reduction of tissue sRANKL, providing an immunological approach to ameliorate immune cell-mediated periodontal bone resorption.

Glycosylation of the collagen adhesin EmaA of Aggregatibacter actinomycetemcomitans is dependent upon the lipopolysaccharide biosynthetic pathway

The human oropharyngeal pathogen Aggregatibacter actinomycetemcomitans synthesizes multiple adhesins, including the nonfimbrial extracellular matrix protein adhesin A (EmaA). EmaA monomers trimerize to form antennae-like structures on the surface of the bacterium, which are required for collagen binding. Two forms of the protein have been identified, which are suggested to be linked with the type of O-polysaccharide (O-PS) of the lipopolysaccharide (LPS) synthesized (G. Tang et al., Microbiology 153:2447-2457, 2007). This association was investigated by generating individual mutants for a rhamnose sugar biosynthetic enzyme (rmlC; TDP-4-keto-6-deoxy-d-glucose 3,5-epimerase), the ATP binding cassette (ABC) sugar transport protein (wzt), and the O-antigen ligase (waaL). All three mutants produced reduced amounts of O-PS, and the EmaA monomers in these mutants displayed a change in their electrophoretic mobility and aggregation state, as observed in sodium dodecyl sulfate (SDS)-polyacrylamide gels. The modification of EmaA with O-PS sugars was suggested by lectin blots, using the fucose-specific Lens culinaris agglutinin (LCA). Fucose is one of the glycan components of serotype b O-PS. The rmlC mutant strain expressing the modified EmaA protein demonstrated reduced collagen adhesion using an in vitro rabbit heart valve model, suggesting a role for the glycoconjugant in collagen binding. These data provide experimental evidence for the glycosylation of an oligomeric, coiled-coil adhesin and for the dependence of the posttranslational modification of EmaA on the LPS biosynthetic machinery in A. actinomycetemcomitans.

Adherence of Aggregatibacter actinomycetemcomitans via serotype-specific polysaccharide antigens in lipopolysaccharides

INTRODUCTION

Gram-negative Aggregatibacter actinomycetemcomitans is recognized as an important periodontal pathogen. A striking property of this bacterium is its ability to form a tenacious biofilm adhering to abiotic surfaces. Both fimbrial and non-fimbrial adhesins are believed to be responsible for this ability. In our study, specific markerless mutants in the biosynthesis genes of cell surface polysaccharides were constructed with the Cre-loxP recombination system to identify non-fimbrial adhesin(s).

METHODS

Non-fimbriated A. actinomycetemcomitans strain ATCC29523 (serotype a) was used to construct a deletion mutant of serotype-a specific polysaccharide antigen (SPA-a) in lipopolysaccharide (LPS). The LPS was purified through a polymyxin B column following phenol extraction, and verified by silver staining following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by immunoblot analysis using rabbit antisera raised against SPA-a. Strains were grown in broth for 2 days and examined for the adherence of bacterial cells on the glass surface.

RESULTS

Strain ATCC29523 formed a thin film of bacterial growth on the glass surface. The deletion of SPA-a affected its ability to form this thin film. When this mutant was rescued with the wild-type SPA-a gene cluster, its adherence-positive phenotype was restored.

CONCLUSION

SPA-a in the LPS molecule appears to promote the adherence of A. actinomycetemcomitans cells to abiotic surfaces.

Detection and serotype distribution of Actinobacillus actinomycetemcomitans in cardiovascular specimens from Japanese patients

Actinobacillus actinomycetemcomitans, an important pathogen in periodontitis, has also been detected in cardiovascular tissues. Sixty heart valves were collected during valve replacement surgery from 60 patients (one from each), 10 were from patients with infective endocarditis (IE group) and 50 were from patients with other valvular diseases (non-IE group). In addition, 46 samples of aneurysmal tissue were taken from 46 patients with a thoracic or abdominal aneurysm (Aneurysm group, one from each). Dental plaque samples were taken from 54 of the patients, 31 in the IE and non-IE groups and 23 in the aneurysm group. First, the distribution of A. actinomycetemcomitans in all specimens was analysed using a polymerase chain reaction method, which resulted in a positive reaction in 33 (31.1%) of the cardiovascular specimens and 25 (46.3%) of the dental plaque samples. Next, using serotype-specific sets of primers, the serotype distribution of A. actinomycetemcomitans in the cardiovascular specimens and dental plaque samples was found to be significantly different compared to dental plaque samples from Japanese subjects reported previously.

Reclassification of Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, Haemophilus paraphrophilus and Haemophilus segnis as Aggregatibacter actinomycetemcomitans gen. nov., comb. nov., Aggregatibacter aphrophilus comb. nov. and Aggregatibacter segnis comb. nov., and emended description of Aggregatibacter aphrophilus to include V factor-dependent and V factor-independent isolates

The aim of this study was to reinvestigate the relationships and the generic affiliations of the species Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, Haemophilus paraphrophilus and Haemophilus segnis. The nicotinamide phosphoribosyltransferase gene (nadV) conferring V factor-independent growth was identified in Haemophilus aphrophilus. The gene encodes a polypeptide of 462 amino acids that shows 74.5 % amino acid sequence identity to the corresponding enzyme from Actinobacillus actinomycetemcomitans. Ten isolates of Haemophilus paraphrophilus all carried a nadV pseudogene. DNA from Haemophilus aphrophilus was able to transform Haemophilus paraphrophilus into the NAD-independent phenotype. The transformants carried a full-length nadV inserted in the former locus of the pseudogene. The DNA–DNA relatedness between the type strains of Haemophilus aphrophilus and Haemophilus paraphrophilus was 77 %. We conclude that the division into two species Haemophilus aphrophilus and Haemophilus paraphrophilus is not justified and that Haemophilus paraphrophilus should be considered a later heterotypic synonym of Haemophilus aphrophilus. Forty strains of Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus and Haemophilus segnis were investigated by multilocus sequence analysis. The 40 strains form a monophyletic group clearly separate from other evolutionary lineages of the family Pasteurellaceae. We propose the transfer of Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus and Haemophilus segnis to a new genus Aggregatibacter gen. nov. as Aggregatibacter actinomycetemcomitans comb. nov. (the type species; type strain ATCC 33384T=CCUG 13227T=CIP 52.106T=DSM 8324T=NCTC 9710T), Aggregatibacter aphrophilus comb. nov. (type strain ATCC 33389T=CCUG 3715T=CIP 70.73T=NCTC 5906T) and Aggregatibacter segnis comb. nov. (type strain HK316T=ATCC 33393T=CCUG 10787T=CCUG 12838T=CIP 103292T=NCTC 10977T). The species of the genus Aggregatibacter are independent of X factor and variably dependent on V factor for growth in vitro.

Coaggregation of Porphyromonas gingivalis and Fusobacterium nucleatum PK 1594 is mediated by capsular polysaccharide and lipopolysaccharide

Previous reports have shown that coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum, two important periodontopathogens, is mediated by a galactoside on the surface of P. gingivalis and a lectin on F. nucleatum. In the present study, purified capsular polysaccharide (CPS) and lipopolysaccharide (LPS) of P. gingivalis PK 1924 (serotype K5) were found to be able to bind to F. nucleatum cells and to inhibit binding of F. nucleatum to P. gingivalis serotype K5. Sugar binding studies showed that the requirements for binding of P. gingivalis serotype K5 CPS and LPS to the F. nucleatum lectin are: the presence of a metal divalent ion, an axial free hydroxyl group at position 4 and free equatorial hydroxyl groups at position 3 and 6 of d-galactose. These data suggest that P. gingivalis serotype K5- CPS and LPS act as receptors mediating coaggregation between P. gingivalis and fusobacteria.

Environmental influences on Actinobacillus actinomycetemcomitans biofilm formation

Fresh clinical isolates of the periodontal pathogen Actinobacillus actinomycetemcomitans have an adherent, rough colony morphology that transforms into a minimally adherent, smooth colony phenotype during successive in vitro passage. The objectives of this study were: (1) to compare biofilm formation of the rough (RVs) and smooth variants (SVs) of several strains of A. actinomycetemcomitans grown under various environmental conditions and (2) to examine the dynamics of biofilm formation. A microtitre plate biofilm assay was used to evaluate biofilm formation of strains grown in broth with modified salt concentration and pH, and to evaluate the effect of pre-conditioning films. Scanning electron microscopy (SEM) was used to monitor microscopic changes in morphology. Dynamics of biofilm formation were measured in a flowcell monitored by confocal microscopy. The RVs generally produced greater biofilm than the SVs. However, medium-dependent differences in biofilm formation were evident for some rough/smooth pairs. The RVs were more tolerant to changes in salt and pH, and more resistant to chlorhexidine than the SVs. Horse serum virtually eliminated, and saliva significantly reduced, biofilm formation by the SVs in contrast to the RVs. SEM revealed no alteration in morphology with change of environment. In a flowcell, the RVs produced towers of microcolonies anchored by a small contact area, whereas the SVs produced an open architecture of reduced height. After 7 days in a flowcell, the rough to smooth phenotype transition could be demonstrated. In conclusion, strain, growth medium and conditioning film all affect biofilm formation. The RVs produce biofilms of unique architecture that may serve to protect the bacterium from environmental perturbations.

Selective blockade of voltage-gated potassium channels reduces inflammatory bone resorption in experimental periodontal disease

The effects of the potassium channel (Kv1.3) blocker kaliotoxin on T-cell-mediated periodontal bone resorption were examined in rats. Systemic administration of kaliotoxin abrogated the bone resorption in conjunction with decreased RANKL mRNA expression by T-cells in gingival tissue. This study suggests a plausible therapeutic approach for inflammatory bone resorption by targeting Kv1.3.

INTRODUCTION

Kv1.3 is a critical potassium channel to counterbalance calcium influx at T-cell receptor activation. It is not known if Kv1.3 also regulates RANKL expression by antigen-activated T-cells, and consequently affects in vivo bone resorption mediated by activated T-cells.

MATERIALS AND METHODS

Actinobacillus actinomycetemcomitans 29-kDa outer membrane protein-specific Th1-clone cells were used to evaluate the expression of Kv1.3 (using reverse transcriptase-polymerase chain reaction [RT-PCR] and Western blot analyses) and the effects of the potassium channel blocker kaliotoxin (0-100 nM) on T-cell activation parameters ([3H]thymidine incorporation assays and ELISA) and expression of RANKL and osteoprotegerin (OPG; flow cytometry, Western blot, and RT-PCR analyses). A rat periodontal disease model based on the adoptive transfer of activated 29-kDa outer membrane protein-specific Th1 clone cells was used to analyze the effects of kaliotoxin in T-cell-mediated alveolar bone resorption and RANKL and OPG mRNA expression by gingival T-cells. Stimulated 29-kDa outer membrane protein-specific Th1 clone cells were transferred intravenously on day 0 to all animals used in the study (n = 7 animals per group). Ten micrograms of kaliotoxin were injected subcutaneously twice per day on days 0, 1, 2, and 3, after adoptive transfer of the T-cells. The control group of rats was injected with saline as placebo on the same days as injections for the kaliotoxin-treated group. The MOCP-5 osteoclast precursor cell line was used in co-culture studies with fixed 29-kDa outer membrane protein-specific Th1-clone cells to measure T-cell-derived RANKL-mediated effects on osteoclastogenesis and resorption pit formation assays in vitro. Statistical significance was evaluated by Student's t-test.

RESULTS

Kaliotoxin decreased T-cell activation parameters of 29-kDa outer membrane protein-specific Th1 clone cells in vitro and in vivo. Most importantly, kaliotoxin administration resulted in an 84% decrease of the bone resorption induced in the saline-treated control group. T-cells recovered from the gingival tissue of kaliotoxin-treated rats displayed lower ratios of RANKL and OPG mRNA expression than those recovered from the control group. The ratio of RANKL and osteoprotegerin protein expression and induction of RANKL-dependent osteoclastogenesis by the activated T-cells were also markedly decreased after kaliotoxin treatments in vitro.

CONCLUSION

The use of kaliotoxin or other means to block Kv1.3 may constitute a potential intervention therapy to prevent alveolar bone loss in periodontal disease.

Outer membrane protein 100, a versatile virulence factor of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans (Aa) is one of the pathogenic bacteria involved in periodontal diseases. We have previously identified six major outer membrane proteins (Omps) of Aa Y4. Among them is an Omp with high molecular mass, designated Omp100, which has homology to a variety of virulence factors. Electron microscopic observation indicated that Omp100 is randomly localized on the cell surface of Aa. Aa Y4 has been shown to adhere and invade KB or normal human gingival keratinocytes. Anti-Omp100 antibody inhibited 50% of adhesion and 70% of invasion of Aa Y4 to KB cells. An Omp100 knock-out mutant had a decreased adhesion and invasion efficiency of 60%, compared with that of the wild type. Escherichia coli HB101 expressing Omp100 adhered twofold and invaded 10-fold more than the wild-type E. coli HB101. HB101 expressing Omp100 showed resistance to serum by trapping factor H, an inhibitor for C3b, with Omp100. Omp100 induced inflammatory cytokine responses of interleukin (IL)-8, IL-6 and tumour necrosis factor (TNF)alpha in epithelial cells, and induced IL-1beta and TNFalpha production in mouse macrophages. These results indicate that Omp100 is a versatile virulence factor that may demonstrate potential significance in the onset of periodontal diseases related to Aa.

Actinobacillus actinomycetemcomitans serotype d-specific antigen contains the O antigen of lipopolysaccharide

Actinobacillus actinomycetemcomitans is a gram-negative, facultatively anaerobic bacterium which is associated especially with aggressive forms of periodontitis. Contradictory results on the localization of the A. actinomycetemcomitans serotype-specific antigen have been reported. The aim of the present study was to characterize the A. actinomycetemcomitans serotype d-specific antigen. The antigen was isolated by affinity chromatography. The affinity column was prepared from immunoglobulin G isolated from rabbit antiserum raised against A. actinomycetemcomitans serotype d. The isolated antigen was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and silver staining, all of which revealed a ladder-like structure typical for the O antigen of lipopolysaccharide (LPS). In a displacement enzyme-linked immunosorbent assay (ELISA), the isolated antigen displaced in a concentration-dependent manner the binding of the polyclonal rabbit antiserum raised against A. actinomycetemcomitans serotype d to the competing whole-cell serotype d antigen. The isolated antigen contained LPS, and an equal concentration of LPS isolated from A. actinomycetemcomitans serotype d gave a similar displacement curve in the ELISA. In order to test the immunogenic properties of the isolated antigen, it was used to immunize a rabbit. The antiserum raised against the isolated antigen displayed specificity in Western blotting and ELISA similar to that of antibody raised against LPS isolated from A. actinomycetemcomitans serotype d. In conclusion, our results show that the A. actinomycetemcomitans serotype d-specific antigen contains the O-antigenic structure of LPS.

Actinobacillus actinomycetemcomitans serotype b lipopolysaccharide mediates coaggregation with Fusobacterium nucleatum

Purified Actinobacillus actinomycetemcomitans serotype b lipopolysaccharide (LPS) was found to be able to bind Fusobacterium nucleatum cells and to inhibit binding of F. nucleatum to A. actinomycetemcomitans serotype b. Sugar binding studies showed that the requirements for binding of A. actinomycetemcomitans serotype b LPS to the F. nucleatum lectin are the presence of a metal divalent ion, an axial free hydroxyl group at position 4, and free equatorial hydroxyl groups at positions 3 and 6 of D-galactose, indicating that the beta-N-acetyl-D-galactosamine in the serotype b LPS trisaccharide repeating unit is the monosaccharide residue recognized by the F. nucleatum lectin. These data strongly suggest that A. actinomycetemcomitans serotype b LPS is one of the receptors responsible for the lactose-inhibitable coaggregation of A. actinomycetemcomitans to fusobacteria.

Population structure and genetic diversity of Actinobacillus actinomycetemcomitans strains isolated from localized juvenile periodontitis patients

The phylogeny of 20 Actinobacillus actinomycetemcomitans strains isolated from patients with localized juvenile periodontitis (LJP) was investigated by using partial sequence analysis of 16S rRNA genes, arbitrarily primed PCR (AP-PCR), and four additional PCR assays that amplified polymorphic regions in the leukotoxin (lkt), cytolethal distending toxin (cdt), major fimbrial subunit (flp-1), and serotype-specific O polysaccharide gene clusters. Our analysis also included four strains isolated from healthy subjects and nine reference strains. We found that A. actinomycetemcomitans strains comprised three major phylogenetic lineages. One lineage consisted of serotype b strains, a second lineage consisted of serotype c strains, and a third lineage consisted of serotype a, d, e, and f strains. 16S rRNA sequences within each lineage were highly conserved (<1% base substitutions), whereas sequences between lineages were exceptionally divergent (1.9 to 5.0% substitutions). Two strains exhibited 16S rRNA sequences that were even more distantly related to those of the three major lineages (2.7 to 6.7% substitutions), indicating that additional minor lineages or variants exist. The distribution of 16S rRNA sequences and lkt, cdt, flp-1, and AP-PCR genotypes was consistent with a clonal population structure, with little evidence of assortative recombination between strains of different serotypes. Strains from all three major lineages were recovered from LJP patients, suggesting that phylogenetically diverse strains of A. actinomycetemcomitans carry pathogenic potential.

Structural characterization of the O-antigenic polysaccharide chain of Porphyromonas circumdentaria NCTC 12469

Structural studies were carried out on an O-antigenic polysaccharide moiety derived from Porphyromonas circumdentaria NCTC 12469, a reference strain of Porphyromonas species. The polysaccharide chain was composed of D-glucose, D-galactose, N-acetyl-D-glucosamine, and N-acetyl-D-galactosamine in a molar ratio of 1:2:1:1. On the basis of results from 1H- and 13C-NMR spectroscopic analyses including COSY, TOCSY, and HMQC experiments together with results of Smith degradation, methylation analysis, and partial acid hydrolysis, it is concluded that the polysaccharide chain has a pentasaccharide repeating unit of -->6)-beta-D-Glcp-(1-->6)-beta-D-Galp-(1-->3)-beta-D-GlcpNAc-(1-->3)-beta-D-GalpNAc-(1-->. The immunoreaction between P. circumdentaria LPS and the corresponding antiserum was strongly inhibited by the pentasaccharide fragment (Glc-Gal-Gal-GlcNAc-GalNAc) isolated from partial acid hydrolysis of the above polysaccharide, suggestive of O-antigen specific antibodies in the used antiserum.

Structural and genetic analyses of O polysaccharide from Actinobacillus actinomycetemcomitans serotype f

The oral bacterium Actinobacillus actinomycetemcomitans is implicated as a causative agent of localized juvenile periodontitis (LJP). A. actinomycetemcomitans is classified into five serotypes (a to e) corresponding to five structurally and antigenically distinct O polysaccharide (O-PS) components of their respective lipopolysaccharide molecules. Serotype b has been reported to be the dominant serotype isolated from LJP patients. We determined the lipopolysaccharide O-PS structure from A. actinomycetemcomitans CU1000, a strain isolated from a 13-year-old African-American female with LJP which had previously been classified as serotype b. The O-PS of strain CU1000 consisted of a trisaccharide repeating unit composed of L-rhamnose and 2-acetamido-2-deoxy-D-galactose (molar ratio, 2:1) with the structure -->2)-alpha-L-Rhap-(1-3)-2-O-(beta-D-GalpNAc)-alpha-L-Rhap-(1-->* O-PS from strain CU1000 was structurally and antigenically distinct from the O-PS molecules of the five known A. actinomycetemcomitans serotypes. Strain CU1000 was mutagenized with transposon IS903phikan, and three mutants that were deficient in O-PS synthesis were isolated. All three transposon insertions mapped to a single 1-kb region on the chromosome. The DNA sequence of a 13.1-kb region surrounding these transposon insertions contained a cluster of 14 open reading frames that was homologous to gene clusters responsible for the synthesis of A. actinomycetemcomitans serotype b, c, and e O-PS antigens. The CU1000 gene cluster contained two genes that were not present in serotype-specific O-PS antigen clusters of the other five known A. actinomycetemcomitans serotypes. These data indicate that strain CU1000 should be assigned to a new A. actinomycetemcomitans serotype, designated serotype f. A PCR assay using serotype-specific PCR primers showed that 3 out of 20 LJP patients surveyed (15%) harbored A. actinomycetemcomitans strains carrying the serotype f gene cluster. The finding of an A. actinomycetemcomitans serotype showing serological cross-reactivity with anti-serotype b-specific antiserum suggests that a reevaluation of strains previously classified as serotype b may be warranted.

Requirement of B7 costimulation for Th1-mediated inflammatory bone resorption in experimental periodontal disease

The CD28 costimulation at TCR signaling plays a pivotal role in the regulation of the T cell response. To elucidate the role of T cells in periodontal disease, a system of cell transfer with TCR/CD28-dependent Th1 or Th2 clones was developed in rats. Gingival injection of specific Ag, Actinobacillus actinomycetemcomitans 29-kDa outer membrane protein, and LPS could induce local bone resorption 10 days after the transfer of Ag-specific Th1 clone cells, but not after transfer of Th2 clone cells. Interestingly, the presence of LPS was required not only for the induction of bone resorption but also for Ag-specific IgG2a production. LPS injection elicited the induction of expression of both B7-1 and B7-2 expression on gingival macrophages, which otherwise expressed only MHC class II when animals were injected with Ag alone. The expression of B7 molecules was observed for up to 3 days, which corresponded to the duration of retention of T clone cells in gingival tissues. Either local or systemic administration of CTLA4Ig, a functional antagonist of CD28 binding to B7, could abrogate the bone resorption induced by Th1 clone cells combined with gingival challenge with both Ag and LPS. These results suggest that local Ag-specific activation of Th1-type T cells by B7 costimulation appeared to trigger inflammatory bone resorption, whereas inhibition of B7 expression by CTLA4Ig might be a therapeutic approach for intervention with inflammatory bone resorption.

Altered antigenicity is seen in the lipopolysaccharide profile of non-serotypeable Actinobacillus actinomycetemcomitans strains

Non-serotypeable Actinobacillus actinomycetemcomitans strains may be derived from the serotypeable ones. In the present study, we compared the outer membrane proteins (OMPs) and lipopolysaccharides (LPSs) of serotypeable and non-serotypeable A. actinomycetemcomitans strains (n=24) of the same genotype in the same subject (n=6) to find out if alterations on the cell-surface contribute to the non-serotypeability. Serotypeable and non-serotypeable A. actinomycetemcomitans strains showed great similarity in the OMP patterns both within and between subjects. Using serotype-specific antisera, clear immunoblotting LPS profiles in the O-antigenic region were seen in serotype b and c strains but not in non-serotypeable strains from the same subjects. The results suggest that changes in LPS lead to the altered antigenicity of non-serotypeable A. actinomycetemcomitans strains.

A gene cluster for 6-deoxy-L-talan synthesis in Actinobacillus actinomycetemcomitans

The serotype c antigen of Actinobacillus actinomycetemcomitans consists of 6-deoxy-l-talose. A gene cluster involved in the synthesis of serotype-specific polysaccharide antigen was cloned from the chromosomal DNA of A. actinomycetemcomitans NCTC 9710 (serotype c). This cluster consisted of 17 open reading frames. Escherichia coli produced the polysaccharide that reacts with the serotype c-specific antibody when transformed with a plasmid containing the cluster. Comparing the structure of the gene cluster with a similar cluster from A. actinomycetemcomitans Y4 (serotype b), which produces a polysaccharide consisting of l-rhamnose and d-fucose, revealed that a 5.7 kb region containing seven genes in the cluster from strain Y4 was replaced by a 3.8 kb region containing three genes in strain NCTC 9710. The results suggest that these region, as well as dTDP-6-deoxy-l-talose-forming dTDP-4-keto-l-rhamnose reductase, is essential to the production of extracellular polysaccharide specific to serotype c.