BackgroundGlaucoma is a progressive optic nerve degenerative disease that often leads to blindness. Local inflammatory responses are implicated in the pathology of glaucoma. Although inflammatory episodes outside the CNS, such as those due to acute systemic infections, have been linked to central neurodegeneration, they do not appear to be relevant to glaucoma. Based on clinical observations, we hypothesized that chronic subclinical peripheral inflammation contributes to neurodegeneration in glaucoma.MethodsMouthwash specimens from patients with glaucoma and control subjects were analyzed for the amount of bacteria. To determine a possible pathogenic mechanism, low-dose subcutaneous lipopolysaccharide (LPS) was administered in two separate animal models of glaucoma. Glaucomatous neurodegeneration was assessed in the retina and optic nerve two months later. Changes in gene expression of toll-like receptor 4 (TLR4) signaling pathway and complement as well as changes in microglial numbers and morphology were analyzed in the retina and optic nerve. The effect of pharmacologic blockade of TLR4 with naloxone was determined.FindingsPatients with glaucoma had higher bacterial oral counts compared to control subjects (p<0.017). Low-dose LPS administration in glaucoma animal models resulted in enhancement of axonal degeneration and neuronal loss. Microglial activation in the optic nerve and retina as well as upregulation of TLR4 signaling and complement system were observed. Pharmacologic blockade of TLR4 partially ameliorated the enhanced damage.ConclusionsThe above findings suggest that the oral microbiome contributes to glaucoma pathophysiology. A plausible mechanism by which increased bacterial loads can lead to neurodegeneration is provided by experiments in animal models of the disease and involves activation of microglia in the retina and optic nerve, mediated through TLR4 signaling and complement upregulation. The finding that commensal bacteria may play a role in the development and/or progression of glaucomatous pathology may also be relevant to other chronic neurodegenerative disorders.

Porphyromonas gingivalis is implicated in the etiology of chronic periodontitis. Genotyping studies suggest that genetic variability exists among P. gingivalis strains; however, the extent of variability remains unclear and regions of variability remain largely unidentified. To assess P. gingivalis strain diversity, we previously used heteroduplex analysis of the ribosomal operon intergenic spacer region (ISR) to type strains in clinical samples and identified 22 heteroduplex types. Additionally, we used ISR sequence analysis to determine the relatedness of P. gingivalis strains to one another and demonstrated a link between ISR sequence phylogeny and the disease-associated phenotype of the strains. In the current study, heteroduplex analysis of the ISR was used to determine the worldwide genetic variability and distribution of P. gingivalis, and microarray-based comparative genomic hybridization (CGH) analysis was used to more comprehensively examine the variability of major heteroduplex type strains by using the entire genome. Heteroduplex analysis of clinical samples from geographically diverse populations identified 6 predominant geographically widespread heteroduplex types (prevalence, >5%) and 14 rare heterodpulex types (prevalence, <2%) which are found in one or a few locations. CGH analysis of the genomes of seven clinically prevalent heteroduplex type strains identified 133 genes from strain W83 that were divergent in at least one of the other strains. The relatedness of the strains to one another determined on the basis of genome content (microarray) analysis was highly similar to their relatedness determined on the basis of ISR sequence analysis, and a striking correlation between the genome contents and disease-associated phenotypes of the strains was observed.Porphyromonas gingivalis is a gram-negative anaerobe that has been strongly implicated as a pathogen in adult (chronic) periodontitis (3,15,20,32,39,40), a destructive disease that affects the gingiva and supporting structures of the teeth. The bacterium is found under conditions of both health and disease, with prevalences that range from 10% to 25% in healthy individuals and 79% to 90% in individuals with periodontitis being found (20,23,24). Previous epidemiologic studies have demonstrated that P. gingivalis strains vary with respect to their levels of human disease association (4,5,21). Studies have also demonstrated that P. gingivalis strains vary in their virulence (soft tissue destruction and death) in animal models, with some strains being classified as virulent, e.g., strains W83, W50, ATCC 49417, and A7A1, and others being classified as avirulent, e.g., strains 381, 33277, and 23A4 (19, 25, 37).Many studies have assessed the genetic diversity that exists among P. gingivalis strains, resulting in the finding of a high degree of diversity in some cases (17, 29, 31, 34) and a considerably lower degree of diversity in others (2, 28). The amount of variability found may be due to the different techniques used in the studies. In a previous ...

Porphyromonas gingivalis is a Gram-negative obligate anaerobe that has been implicated in the etiology of adult periodontitis. We recently introduced a Drosophila melanogaster killing model for examination of P. gingivalis-host interactions. In the current study, the Drosophila killing model was used to characterize the host response to P. gingivalis infection by identifying host components that play a role during infection. Drosophila immune response gene mutants were screened for altered susceptibility to killing by P. gingivalis. The Imd signaling pathway was shown to be important for the survival of Drosophila infected by nonencapsulated P. gingivalis strains but was dispensable for the survival of Drosophila infected by encapsulated P. gingivalis strains. The P. gingivalis capsule was shown to mediate resistance to killing by Drosophila antimicrobial peptides (Imd pathway-regulated cecropinA and drosocin) and human beta-defensin 3. Drosophila thiol-ester protein II (Tep II) and Tep IV and the tumor necrosis factor (TNF) homolog Eiger were also involved in the immune response against P. gingivalis infection, while the scavenger receptors Eater and Croquemort played no roles in the response to P. gingivalis infection. This study demonstrates that the Drosophila killing model is a useful high-throughput model for characterizing the host response to P. gingivalis infection and uncovering novel interactions between the bacterium and the host.Porphyromonas gingivalis is a Gram-negative, obligate anaerobe that has been strongly implicated as a pathogen in adult (chronic) periodontitis (23, 29), a polymicrobial inflammatory disease that affects the gingiva and other toothsupporting structures. In order to characterize P. gingivalishost interactions a number of animal infection models have been developed, the most common of which are rodent models (6,20,25,28,40,44). Rodent models have been used to identify P. gingivalis components that are involved in pathogenesis (26,32,43,46,48,52,56,57,67,73) and to characterize the host response to P. gingivalis infection (3,6,7,13,22,31,34,35,41,74).The use of the fruit fly Drosophila melanogaster has been well established for examining host-pathogen interactions (5,16,19,21,53,55,65,66). Numerous studies have demonstrated the high degree of conservation between the Drosophila immune system and the mammalian innate immune system (reviewed in reference 49). Like the mammalian innate immune system, the Drosophila immune system detects the presence of invading microbes by using pattern recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs) and trigger an immune response that is specific for the class of invading microbe. Other mammalian immune response features that are conserved in Drosophila include signaling pathways (e.g., Toll/interleukin-1 receptor [IL1R], tumor necrosis factor receptor [TNFR]), antimicrobial peptides (AMPs), macrophage-like blood cells, complement C3/ ␣ 2 -macroglobulin (C3/␣ 2 M) superfamily proteins, cytokines, react...

Porphyromonas gingivalis has been implicated in the etiology of adult periodontitis. In this study, we examined the viability of Drosophila melanogaster as a new model for examining P. gingivalis-host interactions. P. gingivalis (W83) infection of Drosophila resulted in a systemic infection that killed in a dose-dependent manner. Differences in the virulence of several clinically prevalent P. gingivalis strains were observed in the Drosophila killing model, and the results correlated well with studies in mammalian infection models and human epidemiologic studies. P. gingivalis pathobiology in Drosophila did not result from uncontrolled growth of the bacterium in the Drosophila hemolymph (blood) or overt damage to Drosophila tissues. P. gingivalis killing of Drosophila was multifactorial, involving several bacterial factors that are also involved in virulence in mammals. The results from this study suggest that many aspects of P. gingivalis pathogenesis in mammals are conserved in Drosophila, and thus the Drosophila killing model should be useful for characterizing P. gingivalis-host interactions and, potentially, polymicrobe-host interactions.Porphyromonas gingivalis is a Gram-negative, obligate anaerobe that has been strongly implicated in the etiology of adult (chronic) periodontitis (21, 29), a destructive disease that affects the gums and supporting structures of the teeth. P. gingivalis-host interactions have previously been studied using several animal models, the most common of which are murine models (5,7,18,20,28), including an abscess model (39), a subcutaneous chamber model (24), and a periodontal bone loss model (41). Studies performed using murine models have demonstrated that P. gingivalis strains vary in their ability to cause periodontal bone loss (20, 40) and soft tissue destruction and death (28,43,56) and that strain W83 is highly virulent relative to many other strains of P. gingivalis (28,43,56). Murine models have also been used to identify P. gingivalis components that are important for pathogenesis (25,43,51,59) and to characterize the host response to P. gingivalis infection (6,11,31,35).The fruit fly, Drosophila melanogaster, has been well established as a nonmammalian model for studying host-pathogen interactions (1,17,52,55,63). Drosophila relies solely on an innate immune response to combat invading microbes, and this immune response strongly parallels the mammalian innate immune response (47,48). Like the mammalian innate immune response, Drosophila uses pattern recognition receptors to detect conserved microbial motifs on invading microbes, and the flies activate an immune response that is specific for the type of invading microbe. The absence of an adaptive immune response makes Drosophila useful for studying the interactions between microbes and the host innate immune response, in isolation. Numerous tools exist for the genetic manipulation of Drosophila, and these have been used to generate thousands of transgenic and mutant lines, including lines useful for identifying host fac...

The deleterious and sometimes fatal outcomes of bacterial infectious diseases are the net result of the interactions between the pathogen and the host, and the genetically tractable fruit fly, Drosophila melanogaster, has emerged as a valuable tool for modeling the pathogen–host interactions of a wide variety of bacteria. These studies have revealed that there is a remarkable conservation of bacterial pathogenesis and host defence mechanisms between higher host organisms and Drosophila. This review presents an in-depth discussion of the Drosophila immune response, the Drosophila killing model, and the use of the model to examine bacterial–host interactions. The recent introduction of the Drosophila model into the oral microbiology field is discussed, specifically the use of the model to examine Porphyromonas gingivalis–host interactions, and finally the potential uses of this powerful model system to further elucidate oral bacterial-host interactions are addressed.