Oral pathogens: from dental plaque to cardiac disease

Microbial interactions impact stress tolerance in a model oral community

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

IMPORTANCE

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

Lozenges with probiotic strains enhance oral immune response and health

OBJECTIVE

Probiotics participate in regulating oral microbiota and reducing the prevalence of oral diseases; however, clinical research on probiotics is insufficient. Therefore, in this study, we performed in vitro screening of potential oral protective probiotic strains and then evaluated the clinical efficacy of the selected strains on maintaining oral health.

MATERIALS AND METHODS

Fifty healthy individuals were recruited and randomly assigned into the placebo group and probiotics group, which included three strains of probiotics, Lactobacillus salivarius subs. salicinius AP-32, Lactobacillus paracasei ET-66, and Lactobacillus plantarum LPL28. Each group was blindly administered placebo or probiotics for four weeks.

RESULTS

Next-generation sequencing results showed that the oral microbiota of Lactobacillus salivarius in the oral cavity were significantly increased in subjects supplemented with mixed probiotic lozenges. The anti-bacterial activities of viable probiotics were observed within two weeks. Both IgA levels and Lactobacillus and Bifidobacterium abundances in the oral cavity were significantly increased in the experimental groups, along with a reduced formation of plaque. Most participants reported that their oral health conditions and intestinal symptoms had improved.

CONCLUSIONS

Overall, our clinical study suggests that oral probiotic lozenges may enhance oral immunity, modulate oral microbiota, and improve oral health.

Oral Pathogen Porphyromonas gingivalis Can Escape Phagocytosis of Mammalian Macrophages

Macrophages are phagocytic cells that play a key role in host immune response and clearance of microbial pathogens. Porphyromonas gingivalis is an oral pathogen associated with the development of periodontitis. Escape from macrophage phagocytosis was tested by infecting THP-1-derived human macrophages and RAW 264.7 mouse macrophages with strains of P. gingivalis W83 and 33277 as well as Streptococcus gordonii DL1 and Escherichia coli OP50 at MOI = 100. CFU counts for all intracellular bacteria were determined. Then, infected macrophages were cultured in media without antibiotics to allow for escape and escaping bacteria were quantified by CFU counting. P. gingivalis W83 displayed over 60% of the bacterial escape from the total amount of intracellular CFUs, significantly higher compared to all other bacteria strains. In addition, bacterial escape and re-entry were also tested and P. gingivalis W83, once again, showed the highest numbers of CFUs able to exit and re-enter macrophages. Lastly, the function of the PG0717 gene of P. gingivalis W83 was tested on escape but found not related to this activity. Altogether, our results suggest that P. gingivalis W83 is able to significantly avoid macrophage phagocytosis. We propose this ability is likely linked to the chronic nature of periodontitis.

The Toothbrush Microbiome: Impact of User Age, Period of Use and Bristle Material on the Microbial Communities of Toothbrushes

Toothbrushes play a central role in oral hygiene and must be considered one of the most common articles of daily use. We analysed the bacterial colonization of used toothbrushes by next generation sequencing (NGS) and by cultivation on different media. Furthermore, we determined the occurrence of antibiotic resistance genes (ARGs) and the impact of different bristle materials on microbial growth and survival. NGS data revealed that Enterobacteriaceae, Micrococcaceae, Actinomycetaceae, and Streptococcaceae comprise major parts of the toothbrush microbiome. The composition of the microbiome differed depending on the period of use or user age. While higher fractions of Actinomycetales, Lactobacillales, and Enterobacterales were found after shorter periods, Micrococcales dominated on both toothbrushes used for more than four weeks and on toothbrushes of older users, while in-vitro tests revealed increasing counts of Micrococcus on all bristle materials as well. Compared to other environments, we found a rather low frequency of ARGs. We determined bacterial counts between 1.42 × 10⁶ and 1.19 × 10⁷ cfu/toothbrush on used toothbrushes and no significant effect of different bristles materials on bacterial survival or growth. Our study illustrates that toothbrushes harbor various microorganisms and that both period of use and user age might affect the microbial composition.

Anti-Oral Pathogens of Tecoma stans (L.) and Cassia javanica (L.) Flower Volatile Oils in Comparison with Chlorhexidine in Accordance with Their Folk Medicinal Uses

Background and Objectives: Teeth decay and plaque are complicated problems created by oral pathogens. Tecoma stans (L.) and Cassia javanica (L.) are two ornamental evergreen plants widely distributed in Egypt. These plants are traditionally used for oral hygienic purposes. This study aims to elucidate the volatile oil constituents obtained from the flowers of these plants and evaluate the antimicrobial activity of these volatile oils against specific oral pathogens in comparison to chlorhexidine. Materials and Methods: The flowers obtained from both plants were extracted by n-hexane. GC-MS spectrometry was used to identify the constituents. Minimum inhibitory concentrations (MICs) were measured using tetrazolium salt (2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) (XTT). Results: GC-MS analysis revealed the presence of 32 and 29 compounds, representing 100% of the volatile constituents of Tecoma stans and Cassia javanica, respectively. The GC-MS analysis showed more than 60% of the volatile oil constituents are represented in both plants with different proportions. Chlorhexidine exerted stronger activity than tested plants against all microorganisms. Cassia javanica flower extract was more active against all tested microorganisms than Tecoma stans. Of note was the effect on Streptococcus mutans, which was inhibited by 100% at 12.5 and 25 µg/mL of Cassia javanica and Tecoma stans, respectively. The growth of Lactobacillus acidophilus was also completely inhibited by 25 µg/mL of the Cassia javanica extract. MIC90 and MIC were also calculated, which revealed the superiority of Cassia javanica over Tecoma stans against all tested oral pathogens. Conclusion: Cassia javanica flower volatile oils showed a potential anti-oral pathogen activity at relatively low concentrations. Also, Cassia javanica and Tecoma stans demonstrated a strong activity against tooth decay's notorious bacteria Streptococcus mutans. Both plants can be potential substituents to chlorhexidine. Formulating the constituents of these plants in toothpastes and mouthwashes as anti-oral pathogen preparations can be an interesting future plan.

Ligature-induced periodontitis induces systemic inflammation but does not alter acute outcome after stroke in mice

Background

Stroke is a major cause of disability and mortality. Poorer outcome after stroke is associated with concomitant inflammatory and infectious disease. Periodontitis is a chronic inflammatory disease of the dental supporting structures and is a prominent risk factor for many systemic disorders, including cardiovascular disease and stroke. While epidemiological studies suggest that periodontitis increases the likelihood of stroke, its impact on stroke severity is poorly understood. Here, we sought to determine the contribution of periodontitis to acute stroke pathology.

Methods

We characterized a murine ligature model of periodontitis for inflammatory responses that could potentially impact stroke outcome. We applied this model and then subjected mice to either transient or permanent middle cerebral artery occlusion. We also enhanced the periodontitis model with repeated intravenous administration of a periodontal-specific lipopolysaccharide to better mimic the clinical condition.

Results

Ligature-induced periodontitis caused bone loss, bacterial growth, and increased local inflammatory cell trafficking. Systemically, periodontitis increased circulating levels of pro-inflammatory cytokines, and primed bone marrow monocytes to produce elevated tumour necrosis factor-alpha (TNFα). Despite these changes, periodontitis alone or in tandem with repeated lipopolysaccharide challenge did not alter infarct volume, blood–brain barrier breakdown, or systemic inflammation after experimental stroke.

Conclusions

Our data show that despite elevated systemic inflammation in periodontitis, oral inflammatory disease does not impact acute stroke pathology in terms of severity, determined primarily by infarct volume. This indicates that, at least in this experimental paradigm, periodontitis alone does not alter acute outcome after cerebral ischemia.

Streptococcus sanguinis biofilm formation & interaction with oral pathogens

Caries and periodontitis are the two most common human dental diseases and are caused by dysbiosis of oral flora. Although commensal microorganisms have been demonstrated to protect against pathogens and promote oral health, most previous studies have addressed pathogenesis rather than commensalism. Streptococcus sanguinis is a commensal bacterium that is abundant in the oral biofilm and whose presence is correlated with health. Here, we focus on the mechanism of biofilm formation in S. sanguinis and the interaction of S. sanguinis with caries- and periodontitis-associated pathogens. In addition, since S. sanguinis is well known as a cause of infective endocarditis, we discuss the relationship between S. sanguinis biofilm formation and its pathogenicity in endocarditis.

Himar1 Transposon for Efficient Random Mutagenesis in Aggregatibacter actinomycetemcomitans

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

Insect Analogue to the Lotus Leaf: A Planthopper Wing Membrane Incorporating a Low-Adhesion, Nonwetting, Superhydrophobic, Bactericidal, and Biocompatible Surface

Nature has produced many intriguing and spectacular surfaces at the micro- and nanoscales. These small surface decorations act for a singular or, in most cases, a range of functions. The minute landscape found on the lotus leaf is one such example, displaying antiwetting behavior and low adhesion with foreign particulate matter. Indeed the lotus leaf has often been considered the "benchmark" for such properties. One could expect that there are animal counterparts of this self-drying and self-cleaning surface system. In this study, we show that the planthopper insect wing (Desudaba danae) exhibits a remarkable architectural similarity to the lotus leaf surface. Not only does the wing demonstrate a topographical likeness, but some surface properties are also expressed, such as nonwetting behavior and low adhering forces with contaminants. In addition, the insect-wing cuticle exhibits an antibacterial property in which Gram-negative bacteria (Porphyromonas gingivalis) are killed over many consecutive waves of attacks over 7 days. In contrast, eukaryote cell associations, upon contact with the insect membrane, lead to a formation of integrated cell sheets (e.g., among human stem cells (SHED-MSC) and human dermal fibroblasts (HDF)). The multifunctional features of the insect membrane provide a potential natural template for man-made applications in which specific control of liquid, solid, and biological contacts is desired and required. Moreover, the planthopper wing cuticle provides a "new" natural surface with which numerous interfacial properties can be explored for a range of comparative studies with both natural and man-made materials.

High-throughput Screening of Small Molecule Inhibitors of the Streptococcus Quorum-sensing Signal Pathway

The main components of the quorum-sensing system are expected to be favorable targets for drug development to combat various chronic infectious diseases. ComA of Streptococcus is an ATP-binding cassette transporter containing a peptidase domain (PEP), which is essential for the quorum-sensing signal production. Using high-throughput screening, we found a potent small molecule that suppressed the S. mutans quorum-sensing pathway through inhibition of PEP activity. The compound effectively attenuated the biofilm formation and competence development of S. mutans without inhibiting cell growth. The kinetic and structural studies with this molecule and a related compound unexpectedly revealed an allosteric site of PEP. This relatively hydrophobic site is thought to undergo large structural changes during the catalytic process. These compounds inhibit PEP activity by binding to and suppressing the structural changes of this site. These results showed that PEP is a good target for inhibitors of the Streptococcus quorum-sensing system.

Fine-tuned production of hydrogen peroxide promotes biofilm formation of Streptococcus parasanguinis by a pathogenic cohabitant Aggregatibacter actinomycetemcomitans

Balanced bacterial biofilm communities help to maintain host health. Disturbance of such balance can lead to bacterial dysbiosis and pathogenesis. However, complex and dynamic bacterial interactions within the biofilm communities are poorly understood. In this study, we used a dual-species biofilm consisting of the periodontal pathogen Aggregatibacter actinomycetemcomitans, and a commensal Streptococcus parasanguinis to investigate bacterial interactions since the two organisms have been found to coexist during the development of localized aggressive periodontal disease. We report that A. actinomycetemcomitans promoted biofilm formation of S. parasanguinis in vitro and in vivo. Protein profiling of S. parasanguinis co-cultured with A. actinomycetemcomitans revealed a significant decrease in the protein level of pyruvate oxidase(PoxL), an enzyme required for the generation of hydrogen peroxide (H₂ O₂ ). Consistently, the H₂ O₂ concentration was concurrently decreased. However, the complete removal of H₂ O₂ impaired the biofilm formation. H₂ O₂ at a low concentration range regulated by A. actinomycetemcomitans enhanced the biofilm formation. These results demonstrate that A. actinomycetemcomitans promotes the S. parasanguinis biofilm formation through modulating the production of H₂ O₂ by fine-tuning the expression of poxL, indicating that H₂ O₂ functions as a signaling molecule. Taken together, this report revealed a previously unknown bacteria-bacteria interaction mechanism.

A gecko skin micro/nano structure - A low adhesion, superhydrophobic, anti-wetting, self-cleaning, biocompatible, antibacterial surface

Geckos, and specifically their feet, have attracted significant attention in recent times with the focus centred around their remarkable adhesional properties. Little attention however has been dedicated to the other remaining regions of the lizard body. In this paper we present preliminary investigations into a number of notable interfacial properties of the gecko skin focusing on solid and aqueous interactions. We show that the skin of the box-patterned gecko (Lucasium sp.) consists of dome shaped scales arranged in a hexagonal patterning. The scales comprise of spinules (hairs), from several hundred nanometres to several microns in length, with a sub-micron spacing and a small radius of curvature typically from 10 to 20 nm. This micro and nano structure of the skin exhibited ultralow adhesion with contaminating particles. The topography also provides a superhydrophobic, anti-wetting barrier which can self clean by the action of low velocity rolling or impacting droplets of various size ranges from microns to several millimetres. Water droplets which are sufficiently small (10-100 μm) can easily access valleys between the scales for efficient self-cleaning and due to their dimensions can self-propel off the surface enhancing their mobility and cleaning effect. In addition, we demonstrate that the gecko skin has an antibacterial action where Gram-negative bacteria (Porphyromonas gingivalis) are killed when exposed to the surface however eukaryotic cell compatibility (with human stem cells) is demonstrated. The multifunctional features of the gecko skin provide a potential natural template for man-made applications where specific control of liquid, solid and biological contacts is required.

Antibacterial and phytochemical studies on Calotropis gigantia (L.) R. Br. latex against selected cariogenic bacteria

In vitro antibacterial potential of the chloroform, ethyl acetate, hexane, methanol and aqueous extracts of Calotropis gigantia (L.) R. Br. was evaluated by using five cariogenic bacteria, Actinomyces viscosus, Lactobacillus acidophilus, Lactobacillus casei, Streptococcus mitis and Streptococcus mutans. Agar well diffusion method and minimum inhibitory concentration (MIC) were used for this purpose. The chloroform extracted fraction of latex showed inhibitory effect against S. mutans and L. acidophilus with MIC value of 0.032 and 0.52 mg/mL, respectively. Qualitative investigation on structure elucidation of bioactive compound using IR, NMR and GC-MS techniques revealed the presence of methyl nonanoate, a saturated fatty acid.

Metabolite cross-feeding enhances virulence in a model polymicrobial infection

Microbes within polymicrobial infections often display synergistic interactions resulting in enhanced pathogenesis; however, the molecular mechanisms governing these interactions are not well understood. Development of model systems that allow detailed mechanistic studies of polymicrobial synergy is a critical step towards a comprehensive understanding of these infections in vivo. In this study, we used a model polymicrobial infection including the opportunistic pathogen Aggregatibacter actinomycetemcomitans and the commensal Streptococcus gordonii to examine the importance of metabolite cross-feeding for establishing co-culture infections. Our results reveal that co-culture with S. gordonii enhances the pathogenesis of A. actinomycetemcomitans in a murine abscess model of infection. Interestingly, the ability of A. actinomycetemcomitans to utilize L-lactate as an energy source is essential for these co-culture benefits. Surprisingly, inactivation of L-lactate catabolism had no impact on mono-culture growth in vitro and in vivo suggesting that A. actinomycetemcomitans L-lactate catabolism is only critical for establishing co-culture infections. These results demonstrate that metabolite cross-feeding is critical for A. actinomycetemcomitans to persist in a polymicrobial infection with S. gordonii supporting the idea that the metabolic properties of commensal bacteria alter the course of pathogenesis in polymicrobial communities.

Many bacterial infections are not the result of colonization and persistence of a single pathogenic microbe in an infection site but instead the result of colonization by several. Although the importance of polymicrobial interactions and pathogenesis has been noted by many prominent microbiologists including Louis Pasteur, most studies of pathogenic microbes have focused on single organism infections. One of the primary reasons for this oversight is the lack of robust model systems for studying bacterial interactions in an infection site. Here, we use a model co-culture system composed of the opportunistic oral pathogen Aggregatibacter actinomycetemcomitans and the common oral commensal Streptococcus gordonii to assess the impact of polymicrobial growth on pathogenesis. We found that the abilities of A. actinomycetemcomitans to persist and cause disease are enhanced during co-culture with S. gordonii. Remarkably, this enhanced persistence requires A. actinomycetemcomitans catabolism of L-lactate, the primary metabolite produced by S. gordonii. These data demonstrate that during co-culture growth, S. gordonii provides a carbon source for A. actinomycetemcomitans that is necessary for establishing a robust polymicrobial infection. This study also demonstrates that virulence of an opportunistic pathogen is impacted by members of the commensal flora.

Nasal immunization with a fusion protein consisting of the hemagglutinin A antigenic region and the maltose-binding protein elicits CD11c(+) CD8(+) dendritic cells for induced long-term protective immunity

We assessed the efficacy of a fusion protein consisting of the 25-kDa antigenic region of Porphyromonas gingivalis hemagglutinin A and the Escherichia coli maltose-binding protein (25k-hagA-MBP) as a nasal vaccine for the prevention of oral infection with P. gingivalis. Nasal immunization with 25k-hagA-MBP induced high levels of 25k-hagA-specific serum IgG, serum IgA, and salivary IgA antibodies in a Toll-like receptor 4 (TLR4)-dependent manner. These antibody responses were maintained for at least 1 year after immunization. Analysis of cytokine responses showed that nasal administration of 25k-hagA-MBP induced antigen-specific CD4(+) T cells producing interleukin 4 (IL-4) and IL-5, but not gamma interferon (IFN-γ), in the spleen and cervical lymph nodes (CLNs). Furthermore, increased numbers of CD11c(+) CD8α(+), but not CD11c(+) CD11b(+) or CD11c(+) B220(+), dendritic cells with upregulated expression of CD80, CD86, CD40, and major histocompatibility complex class II (MHC II) molecules were noted in the spleen, CLNs, and nasopharynx-associated lymphoreticular tissues (NALT). Interestingly, when 25k-hagA-MBP or cholera toxin (CT) was given intranasally to enable examination of their presence in neuronal tissues, the amounts of 25k-hagA-MBP were significantly lower than those of CT. Importantly, mice given 25k-hagA-MBP nasally showed a significant reduction in alveolar bone loss caused by oral infection with P. gingivalis, even 1 year after the immunization. These results suggest that 25k-hagA-MBP administered nasally would be an effective and safe mucosal vaccine against P. gingivalis infection and may be an important tool for the prevention of chronic periodontitis in humans.

[Oral infection control in hospitalized patients: an approach to cardiologist and intensive care units doctors]

This paper aims to find the current level of periodontal med-care knowledge, as well as the possible existence of some oral infection control protocol regarding hospitalized patients. Our sample gathered 110 cardiologists and intensive care units doctors selected from medical teams of five Rio de Janeiro hospitals. Preliminary numbers: 75.4% said to have heard something about Periodontal Medicine, although only 30% out of this group admitted to have read something concerning such subject. On the other side, only 2.7% of the sample informed to do consistent information searching along their patients anamnese, while 58.2% out of this group admitted such procedure conditional to the patient's general state at the due moment. Through such numbers, we tend to come up to the conclusion that, be it either through direct or indirect Periodontal Medicine technical information (and consequently with regards to the absolut importance of preservation and control of oral biofilm and its impact on one's systemic health), the matter has been dimly spread among medical groups. The search also revealed the probability that Rio de Janeiro hospitals lack either units or agents designed for prevention and control of oral infection; consequently, such organizations do not have any kind of protocols, reliable or not, concerned to oral infections.

Oral immunization with Porphyromonas gingivalis outer membrane protein and CpGoligodeoxynucleotides elicits T helper 1 and 2 cytokines for enhanced protective immunity

The aim of this study was to evaluate the efficacy of an oral vaccine containing the 40-kDa outer membrane protein of Porphyromonas gingivalis (40K OMP) and synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN) to control oral infection by P. gingivalis. [run on]40K-OMP40K-OMP40K-OMPOral immunization with 40K-OMP plus CpG ODN induced significant 40K-OMP-specific serum IgG, IgA and saliva IgA antibody responses. The 40K-OMP-specific CD4(+) T cells induced by oral 40K-OMP plus CpG ODN produced both Th1 (IFN-gamma) and Th2 (IL-4) cytokines. Furthermore, increased frequencies of CD11c(+)B220(+) DCs and CD11c(+)CD11b(+) DCs with up-regulated expression of CD80, CD86, CD40 and MHC II molecules were noted in spleen, Peyer's patches and cervical lymph nodes. Immunized mice were then infected orally with P. gingivalis to determine whether the immune responses induced by oral 40K-OMP plus CpG ODN were capable of suppressing bone resorption caused by P. gingivalis infection. Mice given 40K-OMP plus CpG ODN showed significantly reduced bone loss associated with oral infection by P. gingivalis.Thus, oral administration of 40K-OMP together with CpG ODN induces Th1- and Th2-type cells, which provide help for protective immunity against P. gingivalis infection. This may be an important tool for prevention of chronic periodontitis.

Lipoproteins and lipoprotein metabolism in periodontal disease

A growing body of evidence indicates that the incidence of atherosclerosis is increased in subjects with periodontitis - a chronic infection of the oral cavity. This article summarizes the evidence that suggests periodontitis shifts the lipoprotein profile to be more proatherogenic. LDL-C is elevated in periodontitis and most studies indicate that triglyceride levels are also increased. By contrast, antiatherogenic HDL tends to be low in periodontitis. Periodontal therapy tends to shift lipoprotein levels to a healthier profile and also reduces subclinical indices of atherosclerosis. In summary, periodontal disease alters lipoprotein metabolism in ways that could promote atherosclerosis and cardiovascular disease.

Aggregatibacter actinomycetemcomitans builds mutualistic biofilm communities with Fusobacterium nucleatum and Veillonella species in saliva

Human oral bacterial pathogens grow in attached multispecies biofilm communities. Unattached cells are quickly removed by swallowing. Therefore, surface attachment is essential for growth, and we investigated multispecies community interactions resulting in mutualistic growth on saliva as the sole nutritional source. We used two model systems, saliva-coated transferable solid-phase polystyrene pegs (peg biofilms) and flow cells with saliva-coated glass surfaces. Fluorescent antibody staining and image analysis were used to quantify the biomass in flow cells, and quantitative real-time PCR with species-specific primers was used to quantify the biomass in peg biofilms. Veillonella sp. strain PK1910, Aggregatibacter actinomycetemcomitans JP2, and Fusobacterium nucleatum ATCC 10953 were unable to grow as single species in flow cells. Only A. actinomycetemcomitans grew after 36 h when peg biofilms remained submerged in saliva from the time of inoculation. Mixed-species coaggregates were used for two- and three-species inoculation. The biomass in two-species biofilms increased in both systems when Veillonella sp. strain PK1910 was present as one of the partners. Enhanced growth of all strains was observed in three-species biofilms in flow cells. Interestingly, in flow cells F. nucleatum and A. actinomycetemcomitans exhibited mutualism, and, although F. nucleatum was unable to grow with either of the other species in the peg system, F. nucleatum stimulated the growth of Veillonella sp. and together these two organisms increased the total biomass of A. actinomycetemcomitans in three-species peg biofilms. We propose that mutualistic two-species and multispecies oral biofilm communities form in vivo and that mutualism between commensal veillonellae and late colonizing pathogens, such as aggregatibacteria, contributes to the development of periodontal disease.

Polymicrobial interactions stimulate resistance to host innate immunity through metabolite perception

Bacteria in the human oral cavity often grow in an attached multispecies biofilm community. Members of this community display defined interactions that have an impact on the physiology of the individual and the group. Here, we show that during coculture growth with streptococci, the oral pathogen Aggregatibacter actinomycetemcomitans displays enhanced resistance to killing by host innate immunity. The mechanism of resistance involves sensing of the streptococcal metabolite hydrogen peroxide by A. actinomycetemcomitans, which stimulates a genetic program resulting in enhanced expression of the complement resistance protein ApiA. The oxidative stress response regulator OxyR mediates induction of apiA transcription, and this induction is required for coculture resistance to killing by human serum. These findings provide evidence that interaction between community members mediates prokaryotic resistance to host innate immunity and reinforce the need to understand how polymicrobial growth affects interaction with the host immune system.

Metabolic network model of a human oral pathogen

The microbial community present in the human mouth is engaged in a complex network of diverse metabolic activities. In addition to serving as energy and building-block sources, metabolites are key players in interspecies and host-pathogen interactions. Metabolites are also implicated in triggering the local inflammatory response, which can affect systemic conditions such as atherosclerosis, obesity, and diabetes. While the genome of several oral pathogens has been sequenced, quantitative understanding of the metabolic functions of any oral pathogen at the system level has not been explored yet. Here we pursue the computational construction and analysis of the genome-scale metabolic network of Porphyromonas gingivalis, a gram-negative anaerobe that is endemic in the human population and largely responsible for adult periodontitis. Integrating information from the genome, online databases, and literature screening, we built a stoichiometric model that encompasses 679 metabolic reactions. By using flux balance approaches and automated network visualization, we analyze the growth capacity under amino-acid-rich medium and provide evidence that amino acid preference and cytotoxic by-product secretion rates are suitably reproduced by the model. To provide further insight into the basic metabolic functions of P. gingivalis and suggest potential drug targets, we study systematically how the network responds to any reaction knockout. We focus specifically on the lipopolysaccharide biosynthesis pathway and identify eight putative targets, one of which has been recently verified experimentally. The current model, which is amenable to further experimental testing and refinements, could prove useful in evaluating the oral microbiome dynamics and in the development of novel biomedical applications.

The periodontal pathogen Porphyromonas gingivalis cleaves apoB-100 and increases the expression of apoM in LDL in whole blood leading to cell proliferation

OBJECTIVE

Several studies support an association between periodontal disease and atherosclerosis with a crucial role for the pathogen Porphyromonas gingivalis. This study aims at investigating the proteolytic and oxidative activity of P. gingivalis on LDL in a whole blood system using a proteomic approach and analysing the effects of P. gingivalis-modified LDL on cell proliferation.

METHODS

The cellular effects of P. gingivalis in human whole blood were assessed using lumi-aggregometry analysing reactive oxygen species production and aggregation. Blood was incubated for 30 min with P. gingivalis, whereafter LDL was isolated and a proteomic approach was applied to examine protein expression. LDL-oxidation was determined by analysing the formation of protein carbonyls. The effects of P. gingivalis-modified LDL on fibroblast proliferation were studied using the MTS assay.

RESULTS

Incubation of whole blood with P. gingivalis caused an extensive aggregation and ROS production, indicating platelet and leucocyte activation. LDL prepared from bacteria-exposed blood showed an increased protein oxidation, elevated levels of apoM and formation of two apoB-100 N-terminal fragments. Porphyromonas gingivalis-modified LDL markedly increased the growth of fibroblasts. Inhibition of gingipain R suppressed the modification of LDL by P. gingivalis.

CONCLUSIONS

The ability of P. gingivalis to change the protein expression and proliferative capacity of LDL may represent a crucial event in periodontitis-associated atherosclerosis.

Nasal vaccination with the 40-kilodalton outer membrane protein of Porphyromonas gingivalis and a nontoxic chimeric enterotoxin adjuvant induces long-term protective immunity with reduced levels of immunoglobulin E antibodies

In this study, we demonstrated that the 40-kDa outer membrane protein of Porphyromonas gingivalis (40-kDa OMP) nasally administered with a nontoxic chimeric adjuvant that combines the A subunit of mutant cholera toxin E112K with the pentameric B subunit of heat-labile enterotoxin from enterotoxigenic Escherichia coli (mCTA/LTB) elicited a long-term protective immune response. Immunization with the 40-kDa OMP and mCTA/LTB induced high levels of 40-kDa-OMP-specific immunoglobulin G (IgG) and IgA antibodies (Abs) in sera and elicited a significant IgA anti-40-kDa OMP Ab response in saliva. These Ab responses were maintained for at least 1 year after the immunization. Although using adjuvant mCTA/LTB gave Ab responses in the saliva comparable to those obtained using native cholera toxin (nCT) as the adjuvant, the levels of total IgE and 40-kDa-OMP-specific IgE Abs as well as interleukin-4 levels induced by the immunization with mCTA/LTB were lower than those induced by the immunization with nCT. Importantly, IgG Abs generated by nasal immunization with the 40-kDa OMP plus mCTA/LTB inhibited the coaggregation and hemagglutinin activities of P. gingivalis. Furthermore, the mice given nasal 40-kDa OMP plus mCTA/LTB showed a significant reduction of alveolar bone loss caused by oral infection with P. gingivalis even 1 year after the immunization compared to the loss in unimmunized mice. Because mCTA/LTB is nontoxic, nasally administered 40-kDa OMP together with mCTA/LTB should be an effective and safe mucosal vaccine against P. gingivalis infection in humans and may be an important tool for the prevention of chronic periodontitis.

Adaptive expression of foreign genes in the clonal variants of bacteria: from proteomics to clinical application

Clonal variants of bacteria are able to colonize environmental niches and patients. The factors, that determine the interplay between the colonization of diverse habitats and adaptation, are acquired through horizontal gene transfer. Elucidation of mechanisms, which lead to the prevalence of dominant bacterial clones in patients and the environment, requires the knowledge of complex phenotypes. It was found in the genomes of most bacteria, that upon a conserved chromosomal backbone there were regions of plasticity achieved by insertions, deletions and rearrangements of genomic islands and islets as well as large chromosomal inversions. However, it had been shown that environmental and clinical isolates are indistinguishable in certain pathogenic and biodegradative properties. For example, clonal variants of Pseudomonas aeruginosa exhibit convergent phenotypes despite the presence of numerous DNA insertions in the genome. Apart from this feature, expression of a few genes from the acquired genetic material is important for niche-based adaptation of this organism. Protein expression patterns at the cellular and sub-cellular levels showed common virulence factors and novel drug targets among clonal variants of bacteria. This review will give a short overview on proteomics of different clonal variants of bacteria with respect to clinical applications.

Transcriptional regulation of the tad locus in Aggregatibacter actinomycetemcomitans: a termination cascade

The tad (tight adherence) locus of Aggregatibacter actinomycetemcomitans includes genes for the biogenesis of Flp pili, which are necessary for bacterial adhesion to surfaces, biofilm formation, and pathogenesis. Although studies have elucidated the functions of some of the Tad proteins, little is known about the regulation of the tad locus in A. actinomycetemcomitans. A promoter upstream of the tad locus was previously identified and shown to function in Escherichia coli. Using a specially constructed reporter plasmid, we show here that this promoter (tadp) functions in A. actinomycetemcomitans. To study expression of the pilin gene (flp-1) relative to that of tad secretion complex genes, we used Northern hybridization analysis and a lacZ reporter assay. We identified three terminators, two of which (T1 and T2) can explain flp-1 mRNA abundance, while the third (T3) is at the end of the locus. T1 and T3 have the appearance and behavior of intrinsic terminators, while T2 has a different structure and is inhibited by bicyclomycin, indicating that T2 is probably Rho dependent. To help achieve the appropriate stoichiometry of the Tad proteins, we show that a transcriptional-termination cascade is important to the proper expression of the tad genes. These data indicate a previously unreported mechanism of regulation in A. actinomycetemcomitans and lead to a more complete understanding of its Flp pilus biogenesis.

Substrate recognition mechanism of the peptidase domain of the quorum-sensing-signal-producing ABC transporter ComA from Streptococcus

ComA of Streptococcus is a member of the bacteriocin-associated ABC transporters, which is responsible for both the processing of the propeptide ComC and secretion of the mature quorum-sensing signal. The quorum-sensing system is a bacterial intercellular communication system implicated in various functions including biofilm formation. In this study, the peptidase domains (PEPs) of the ComAs from six species of Streptococcus and ComCs from four species were expressed, purified, and characterized to address the mechanism of the substrate recognition of PEP. PEPs specifically cleaved ComCs after the Gly-Gly site in all the PEP-ComC combinations examined. The N-terminal leader region of ComC was found to form an amphiphilic alpha-helix structure upon binding to the PEP. Furthermore, mutagenesis studies revealed that four conserved hydrophobic residues in this leader region of ComC extending from -15 to -4 positions are critical in the interaction with PEP. Together with the double glycine motif, these structural features of ComC would explain the strict substrate specificity of the PEP.

An aboriginal and Torres Strait Islander oral health curriculum framework: development experiences in Western Australia

Indigenous oral health is widely acknowledged as paralleling the significant issues faced in general health. It is recognized that as part of the process of addressing these issues, practitioners need to be aware of the complex nature of working in an Indigenous social and cultural context, including issues beyond direct health care services. It is against this backdrop that collaborators from The University of Western Australia's (UWA) Centre for Rural and Remote Oral Health (CRROH) and Centre for Aboriginal Medical and Dental Health (CAMDH) developed a comprehensive, integrated Indigenous Oral Health Curriculum Framework for the Bachelor of Dental Science (BDSc) course. This development was based on the existing framework developed by the Committee of Deans of Australian Medical Schools (CDAMS) for medical education but was tailored to the specific issues and needs of oral health. Additional consultation with the Oral Health Centre of Western Australia (OHCWA), the School of Indigenous Studies (SIS) as well as Indigenous Australian groups occurred to ensure the development process was inclusive. The inclusion of an Indigenous Oral Health Curriculum Framework in the BDSc will enable UWA dental graduates to practise dentistry in a culturally appropriate manner. The framework provides the structure for students to develop and demonstrate an understanding of Indigenous histories, cultures and social experiences and how these impact on Indigenous peoples' health. It is anticipated that this will foster more positive and culturally secure patient-practitioner interactions between UWA dental graduates and Indigenous Australians, thereby making it more likely for Indigenous Australians to present for treatment. The increased awareness of Indigenous oral health issues will hopefully encourage more graduates to become involved in the treatment of Indigenous peoples. The combination of these factors could lead to an improvement in oral health outcomes for Australia's Indigenous peoples and a concomitant positive impact on the general health of Indigenous Australians.

The tad locus: postcards from the widespread colonization island

The Tad (tight adherence) macromolecular transport system, which is present in many bacterial and archaeal species, represents an ancient and major new subtype of type II secretion. The tad genes are present on a genomic island named the widespread colonization island (WCI), and encode the machinery that is required for the assembly of adhesive Flp (fimbrial low-molecular-weight protein) pili. The tad genes are essential for biofilm formation, colonization and pathogenesis in the genera Aggregatibacter (Actinobacillus), Haemophilus, Pasteurella, Pseudomonas, Yersinia, Caulobacter and perhaps others. Here we review the structure, function and evolution of the Tad secretion system.

The TadV protein of Actinobacillus actinomycetemcomitans is a novel aspartic acid prepilin peptidase required for maturation of the Flp1 pilin and TadE and TadF pseudopilins

The tad locus of Actinobacillus actinomycetemcomitans encodes genes for the biogenesis of Flp pili, which allow the bacterium to adhere tenaciously to surfaces and form strong biofilms. Although tad (tight adherence) loci are widespread among bacterial and archaeal species, very little is known about the functions of the individual components of the Tad secretion apparatus. Here we characterize the mechanism by which the pre-Flp1 prepilin is processed to the mature pilus subunit. We demonstrate that the tadV gene encodes a prepilin peptidase that is both necessary and sufficient for proteolytic maturation of Flp1. TadV was also found to be required for maturation of the TadE and TadF pilin-like proteins, which we term pseudopilins. Using site-directed mutagenesis, we show that processing of pre-Flp1, pre-TadE, and pre-TadF is required for biofilm formation. Mutation of a highly conserved glutamic acid residue at position +5 of Flp1, relative to the cleavage site, resulted in a processed pilin that was blocked in assembly. In contrast, identical mutations in TadE or TadF had no effect on biofilm formation, indicating that the mechanisms by which Flp1 pilin and the pseudopilins function are distinct. We also determined that two conserved aspartic acid residues in TadV are critical for function of the prepilin peptidase. Together, our results indicate that the A. actinomycetemcomitans TadV protein is a member of a novel subclass of nonmethylating aspartic acid prepilin peptidases.

Leukotoxin confers beta-hemolytic activity to Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is the etiologic agent of localized aggressive periodontitis, a rapidly progressing oral disease that occurs in adolescents. A. actinomycetemcomitans can also cause systemic disease, including infective endocarditis. In early work on A. actinomycetemcomitans workers concluded that this bacterium is not beta-hemolytic. More recent reports have suggested that A. actinomycetemcomitans does have the potential to be beta-hemolytic. While growing A. actinomycetemcomitans on several types of growth media, we noticed a beta-hemolytic reaction on media from one manufacturer. Beta-hemolysis occurred on Columbia agar from Accumedia with either sheep or horse blood, but not on similar media from other manufacturers. A surprising result was that mutants of A. actinomycetemcomitans defective for production of leukotoxin, a toxin that is reportedly highly specific for only human and primate white blood cells, are not beta-hemolytic. Purified leukotoxin was able to lyse sheep and human erythrocytes in vitro. This work showed that in contrast to the accepted view, A. actinomycetemcomitans leukotoxin can indeed destroy erythrocytes and that the production of this toxin results in beta-hemolytic colonies on solid medium. In light of these results, the diagnostic criteria for clinical identification of A. actinomycetemcomitans and potentially related bacteria should be reevaluated. Furthermore, in studies on A. actinomycetemcomitans leukotoxin workers should now consider this toxin's ability to destroy red blood cells.

In vitro antimicrobial and resistance-modifying activities of aqueous crude khat extracts against oral microorganisms

OBJECTIVES

To assess antimicrobial activities of aqueous crude khat (Catha edulis) extracts against a panel of oral microorganisms and to test their ability to modify bacterial resistance to tetracycline and penicillin in vitro.

DESIGN

Lyophilized aqueous extracts were prepared from three khat cultivars. The agar dilution method of the NCCLS was used to test the extracts, at concentrations of 20-1.25 mg/ml, against 33 oral strains. MIC was defined as the lowest concentration at which there was no visible growth. Slight growth was defined as marked growth reduction (MGR). The E-test was used to determine the MICs of tetracycline and penicillin-G for three resistant strains in absence and presence of a sub-MIC of the khat extracts (5mg/ml).

RESULTS

Eighteen strains (55%) were sensitive to the extracts (MICs 5-20 mg/ml). Most of these were periodontal pathogens with Porphyromonas gingivalis and Tannerella forsythensis being the most susceptible (MIC 5-10mg/ml). Veillonella parvula, Actinomyces israelii and some streptococci were not sensitive. Except for Lactobacillus acidophilus that showed MGR at 1mg/ml, cariogenic species were neither sensitive. The extracts were active against Streptococcus pyogenes (MIC 10-20 mg/ml) but not against Candida albicans and Staphylococcus aureus. The presence of the khat extracts at a sub-MIC resulted in a 2-4-fold potentiation of the tested antibiotics against the resistant strains.

CONCLUSIONS

Khat has water-soluble constituents possessing selective antibacterial activity against oral bacteria. There is preliminary evidence for presence of an antibiotic resistance-modifying component. Further investigation is needed to identify the active components and assess their clinical relevance.

Application of sequence-based methods in human microbial ecology

Ecologists studying microbial life in the environment have recognized the enormous complexity of microbial diversity for many years, and the development of a variety of culture-independent methods, many of them coupled with high-throughput DNA sequencing, has allowed this diversity to be explored in ever-greater detail. Despite the widespread application of these new techniques to the characterization of uncultivated microbes and microbial communities in the environment, their application to human health and disease has lagged. Because DNA-based techniques for defining uncultured microbes allow not only cataloging of microbial diversity but also insight into microbial functions, investigators are beginning to apply these tools to the microbial communities that abound on and within us, in what has aptly been called "the second Human Genome Project." In this review we discuss the sequence-based methods for microbial analysis that are currently available and their application to identify novel human pathogens, improve diagnosis of known infectious diseases, and advance understanding of our relationship with microbial communities that normally reside in and on the human body.

Characterization of leukotoxin from a clinical strain of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a Gram negative pathogen that is the etiologic agent of localized aggressive periodontitis (LAP), a rapidly progressing and severe disease of the oral cavity that affects predominantly adolescents. A. actinomycetemcomitans is also found in extraoral infections including infective endocarditis. As one of its many virulence determinants, A. actinomycetemcomitans produces the RTX (repeats in toxin) exotoxin, leukotoxin (LtxA). LtxA specifically kills leukocytes of humans and Old World Monkeys. All of our current knowledge of A. actinomycetemcomitans LtxA is based on the protein from strain JP2, a nonadherent laboratory isolate. Because laboratory isolates can lose virulence properties, we wished to examine LtxA from a clinical isolate, NJ4500. We show that localization patterns of LtxA do not differ between the strains. Subcellular localization studies with NJ4500 revealed that LtxA localizes to the outer membrane and that the interaction between LtxA and the surface of cells is specific. Surface localized LtxA was not removed with NaCl treatment and protease protection experiments revealed that approximately 10 kDa of LtxA is exposed. We purified secreted LtxA from NJ4500 and found that the specific activity of this toxin was greater than that of secreted LtxA from JP2. For other RTX toxins, fatty acid modification affects toxin activity, and A. actinomycetemcomitans LtxA is predicted to be modified. We show by two-dimensional gel electrophoresis that NJ4500 LtxA is more highly modified than JP2 LtxA, suggesting that the difference in activities could be due to differential modification. Studies of A. actinomycetemcomitans pathogenesis should therefore consider LtxA from clinical isolates.

Transcutaneous immunization with a 40-kDa outer membrane protein of Porphyromonas gingivalis induces specific antibodies which inhibit coaggregation by P. gingivalis

This study seeks to assess the potential of a 40-kDa outer membrane protein of Porphyromonas gingivalis (40k-OMP) as a transcutaneous vaccine against chronic periodontitis. Transcutaneous immunization (TCI) of mice with 40k-OMP alone elicited 40k-OMP-specific IgG antibody (Ab) responses in both serum and saliva. When administered with cholera toxin (CT) as adjuvant, TCI with 40k-OMP not only elevated IgG Abs as noted above, but also induced IgA responses in serum but not in saliva. Salivary IgG from mice given 40k-OMP alone or 40k-OMP plus CT showed higher binding levels to the 40k-OMP than did that of non-immunized mice. Ab-forming cell (AFC) analysis revealed high numbers of 40k-OMP-specific IgG AFCs in the spleen but low numbers in the salivary glands of mice given 40k-OMP alone or 40k-OMP plus CT. Since 40k-OMP-specific IgG inhibited the coaggregation of P. gingivalis vesicles and S. gordonii, TCI with 40k-OMP may be a useful tool in the quest to prevent P. gingivalis infection.

Cholesterol synthesis is the trigger and isoprenoid dependent interleukin-6 mediated inflammation is the common causative factor and therapeutic target for atherosclerotic vascular disease and age-related disorders including osteoporosis and type 2 diabetes

This is a unifying theory that cholesterol metabolites (isoprenoids) are an integral component of the signaling pathway for interleukin-6 (IL-6) mediated inflammation. IL-6 inflammation is the common causative origin for atherosclerosis, peripheral vascular disease, coronary artery disease, and age-related disorders including osteoporosis, dementia, Alzheimer's disease and type 2 diabetes. Therapeutic effects of bisphosphonates and statins are mediated by isoprenoid depletion. Statins and bisphosphonates act in the cholesterol pathway to deplete isoprenoids. Anti-inflammatory properties of statins and bisphosphonates are due to isoprenoid depletion with subsequent inhibition of IL-6 mediated inflammation. Therapeutic targets for the prevention and control of all the above diseases should focus on cholesterol metabolites and IL-6 mediated inflammation. Prevention of atherosclerotic vascular disease and age-related disorders will be by utilization of cholesterol lowering agents or techniques and/or treatment with statins and/or bisphosphonates to inhibit IL-6 inflammation through regulation of cholesterol metabolism.

Specific antibodies induced by nasally administered 40-kDa outer membrane protein of Porphyromonas gingivalis inhibits coaggregation activity of P. gingivalis

In this study, we have assessed the efficacy of the 40-kDa outer membrane protein (40k-OMP) of Porphyromonas gingivalis as a nasal vaccine for the prevention of adult periodontitis. Mice nasally immunized with 40k-OMP and cholera toxin as mucosal adjuvant displayed significant levels of 40k-OMP-specific serum IgG1, IgG2b and IgA as well as mucosal IgA antibodies (Abs) in saliva and nasal secretions. Ab-forming cell (AFC) analysis confirmed the antibody titers by detecting high numbers of 40k-OMP-specific AFCs in spleen, salivary glands and nasal passages. Because 40k-OMP-specific IgG inhibited coaggregation of P. gingivalis vesicles and S. gordonii, it may be an important tool for the prevention of adult periodontitis.

Purification and characterization of an immunogenic aminopeptidase of Brucella melitensis

An immunogenic aminopeptidase was purified from Brucella melitensis strain VTRM1. The purification procedure consisted of ammonium sulfate fractionation and three chromatographic steps. This procedure resulted in a yield of 29% and a 144-fold increase in specific activity. The aminopeptidase appeared to be a monomeric enzyme with a molecular mass of 96 kDa and an isoelectric point of 4.8. Its activity was optimal at pH 7.0 at 40 degrees C. The enzyme was strongly inhibited by EDTA, 1,10-phenathroline, and divalent cations (Zn(2+) and Hg(2+)), suggesting that this protein was a metalloaminopeptidase. The enzyme showed preference for alanine at the N termini of aminoacyl derivatives. The K(m) values for L-alanine-p-nitroanilide (Ala-pNA) and Lys-pNA were 0.35 and 0.18 mM, respectively. The N-terminal sequence of aminopeptidase was used for a homologous search in the genomes of B. melitensis 16M and Brucella suis 1330. The analysis revealed an exact match of the probe sequence (36 bp) with an open reading frame of 2,652 bp encoding a protein predicted to be alanyl aminopeptidase (aminopeptidase N). Collectively, these data suggest designation of the B. melitensis enzyme as an aminopeptidase N. The aminopeptidase was recognized by sera from patients with acute and chronic brucellosis, suggesting that the enzyme may have important diagnostic implications.

Complete genome sequence of the oral pathogenic Bacterium porphyromonas gingivalis strain W83

The complete 2,343,479-bp genome sequence of the gram-negative, pathogenic oral bacterium Porphyromonas gingivalis strain W83, a major contributor to periodontal disease, was determined. Whole-genome comparative analysis with other available complete genome sequences confirms the close relationship between the Cytophaga-Flavobacteria-Bacteroides (CFB) phylum and the green-sulfur bacteria. Within the CFB phyla, the genomes most similar to that of P. gingivalis are those of Bacteroides thetaiotaomicron and B. fragilis. Outside of the CFB phyla the most similar genome to P. gingivalis is that of Chlorobium tepidum, supporting the previous phylogenetic studies that indicated that the Chlorobia and CFB phyla are related, albeit distantly. Genome analysis of strain W83 reveals a range of pathways and virulence determinants that relate to the novel biology of this oral pathogen. Among these determinants are at least six putative hemagglutinin-like genes and 36 previously unidentified peptidases. Genome analysis also reveals that P. gingivalis can metabolize a range of amino acids and generate a number of metabolic end products that are toxic to the human host or human gingival tissue and contribute to the development of periodontal disease.

Genomics of oral bacteria

Advances in bacterial genetics came with the discovery of the genetic code, followed by the development of recombinant DNA technologies. Now the field is undergoing a new revolution because of investigators' ability to sequence and assemble complete bacterial genomes. Over 200 genome projects have been completed or are in progress, and the oral microbiology research community has benefited through projects for oral bacteria and their non-oral-pathogen relatives. This review describes features of several oral bacterial genomes, and emphasizes the themes of species relationships, comparative genomics, and lateral gene transfer. Genomics is having a broad impact on basic research in microbial pathogenesis, and will lead to new approaches in clinical research and therapeutics. The oral microbiota is a unique community especially suited for new challenges to sequence the metagenomes of microbial consortia, and the genomes of uncultivable bacteria.