Summary
The microbiota plays a central role in human health and disease by shaping immune development, immune responses and metabolism, and by protecting from invading pathogens. Technical advances ...that allow comprehensive characterization of microbial communities by genetic sequencing have sparked the hunt for disease‐modulating bacteria. Emerging studies in humans have linked the increased abundance of Prevotella species at mucosal sites to localized and systemic disease, including periodontitis, bacterial vaginosis, rheumatoid arthritis, metabolic disorders and low‐grade systemic inflammation. Intriguingly, Prevotella abundance is reduced within the lung microbiota of patients with asthma and chronic obstructive pulmonary disease. Increased Prevotella abundance is associated with augmented T helper type 17 (Th17) ‐mediated mucosal inflammation, which is in line with the marked capacity of Prevotella in driving Th17 immune responses in vitro. Studies indicate that Prevotella predominantly activate Toll‐like receptor 2, leading to production of Th17‐polarizing cytokines by antigen‐presenting cells, including interleukin‐23 (IL‐23) and IL‐1. Furthermore, Prevotella stimulate epithelial cells to produce IL‐8, IL‐6 and CCL20, which can promote mucosal Th17 immune responses and neutrophil recruitment. Prevotella‐mediated mucosal inflammation leads to systemic dissemination of inflammatory mediators, bacteria and bacterial products, which in turn may affect systemic disease outcomes. Studies in mice support a causal role of Prevotella as colonization experiments promote clinical and inflammatory features of human disease. When compared with strict commensal bacteria, Prevotella exhibit increased inflammatory properties, as demonstrated by augmented release of inflammatory mediators from immune cells and various stromal cells. These findings indicate that some Prevotella strains may be clinically important pathobionts that can participate in human disease by promoting chronic inflammation.
Several recent studies link Prevotella colonization at mucosal sites with chronic inflammatory disorders, including periodontitis, bacterial vaginosis, rheumatoid arthritis, metabolic disorders and low‐grade systemic inflammation. This review focuses on the interaction between Prevotella and the immune system, and how Prevotella may promote disease pathology by exacerbating Th17‐mediated inflammation.
Porphyromonas gingivalis is an established pathogen in periodontal disease and an emerging pathogen in serious systemic conditions, including some forms of cancer. We investigated the effect of P. ...gingivalis on β-catenin signaling, a major pathway in the control of cell proliferation and tumorigenesis. Infection of gingival epithelial cells with P. gingivalis did not influence the phosphorylation status of β-catenin but resulted in proteolytic processing. The use of mutants deficient in gingipain production, along with gingipain-specific inhibitors, revealed that gingipain proteolytic activity was required for β-catenin processing. The β-catenin destruction complex components Axin1, adenomatous polyposis coli (APC), and GSK3β were also proteolytically processed by P. gingivalis gingipains. Cell fractionation and Western blotting demonstrated that β-catenin fragments were translocated to the nucleus. The accumulation of β-catenin in the nucleus following P. gingivalis infection was confirmed by immunofluorescence microscopy. A luciferase reporter assay showed that P. gingivalis increased the activity of the β-catenin-dependent TCF/LEF promoter. P. gingivalis did not increase Wnt3a mRNA levels, a finding consistent with P. gingivalis-induced proteolytic processing causing the increase in TCF/LEF promoter activity. Thus, our data indicate that P. gingivalis can induce the noncanonical activation of β-catenin and disassociation of the β-catenin destruction complex by gingipain-dependent proteolytic processing. β-Catenin activation in epithelial cells by P. gingivalis may contribute to a proliferative phenotype.
Diverse microbial signatures within the intestinal microbiota have been associated with intestinal and systemic inflammatory diseases, but whether these candidate microbes actively modulate host ...phenotypes or passively expand within the altered microbial ecosystem is frequently not known. Here we demonstrate that colonization of mice with a member of the genus Prevotella, which has been previously associated to colitis in mice, exacerbates intestinal inflammation. Our analysis revealed that Prevotella intestinalis alters composition and function of the ecosystem resulting in a reduction of short-chain fatty acids, specifically acetate, and consequently a decrease in intestinal IL-18 levels during steady state. Supplementation of IL-18 to Prevotella-colonized mice was sufficient to reduce intestinal inflammation. Hence, we conclude that intestinal Prevotella colonization results in metabolic changes in the microbiota, which reduce IL-18 production and consequently exacerbate intestinal inflammation, and potential systemic autoimmunity.
Objective
To examine the degree to which shared risk factors explain the relationship of periodontitis (PD) to rheumatoid arthritis (RA) and to determine the associations of PD and Porphyromonas ...gingivalis with pathologic and clinical features of RA.
Methods
Patients with RA (n = 287) and patients with osteoarthritis as disease controls (n = 330) underwent a standardized periodontal examination. The HLA–DRB1 status of all participants was imputed using single‐nucleotide polymorphisms from the extended major histocompatibility complex. Circulating anti–P gingivalis antibodies were measured using an enzyme‐linked immunosorbent assay, and subgingival plaque was assessed for the presence of P gingivalis using polymerase chain reaction (PCR). Associations of PD with RA were examined using multivariable regression.
Results
Presence of PD was more common in patients with RA and patients with anti–citrullinated protein antibody (ACPA)–positive RA (n = 240; determined using the anti–cyclic citrullinated peptide 2 anti–CCP‐2 test) than in controls (35% and 37%, respectively, versus 26%; P = 0.022 and P = 0.006, respectively). There were no differences between RA patients and controls in the levels of anti–P gingivalis or the frequency of P gingivalis positivity by PCR. The anti–P gingivalis findings showed a weak, but statistically significant, association with the findings for both anti–CCP‐2 (r = 0.14, P = 0.022) and rheumatoid factor (RF) (r = 0.19, P = 0.001). Presence of PD was associated with increased swollen joint counts (P = 0.004), greater disease activity according to the 28‐joint Disease Activity Score using C‐reactive protein level (P = 0.045), and higher total Sharp scores of radiographic damage (P = 0.015), as well as with the presence and levels of anti–CCP‐2 (P = 0.011) and RF (P < 0.001). The expression levels of select ACPAs (including antibodies to citrullinated filaggrin) were higher in patients with subgingival P gingivalis and in those with higher levels of anti–P gingivalis antibodies, irrespective of smoking status. Associations of PD with established seropositive RA were independent of all covariates examined, including evidence of P gingivalis infection.
Conclusion
Both PD and P gingivalis appear to shape the autoreactivity of RA. In addition, these results demonstrate an independent relationship between PD and established seropositive RA.
Periodontal disease is a polymicrobial inflammatory disease that leads to chronic systemic inflammation and direct infiltration of bacteria/bacterial components, which may contribute to the ...development of Alzheimer's disease. ApoE-/- mice were orally infected (n = 12) with Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, and Fusobacterium nucleatum as mono- and polymicrobial infections. ApoE-/- mice were sacrificed following 12 and 24 weeks of chronic infection. Bacterial genomic DNA was isolated from all brain tissues except for the F. nucleatum mono-infected group. Polymerase chain reaction was performed using universal 16 s rDNA primers and species-specific primer sets for each organism to determine whether the infecting pathogens accessed the brain. Sequencing amplification products confirmed the invasion of bacteria into the brain during infection. The innate immune responses were detected using antibodies against complement activation products of C3 convertase stage and the membrane attack complex. Molecular methods demonstrated that 6 out of 12 ApoE-/- mice brains contained P. gingivalis genomic DNA at 12 weeks (p = 0.006), and 9 out of 12 at 24 weeks of infection (p = 0.0001). Microglia in both infected and control groups demonstrated strong intracellular labeling with C3 and C9, due to on-going biosynthesis. The pyramidal neurons of the hippocampus in 4 out of 12 infected mice brains demonstrated characteristic opsonization with C3 activation fragments (p = 0.032). These results show that the oral pathogen P. gingivalis was able to access the ApoE-/- mice brain and thereby contributed to complement activation with bystander neuronal injury.
In addition to functioning as detergents that aid digestion of dietary lipids in the intestine, some bile acids have been shown to exhibit antimicrobial activity. However, detailed information on the ...bactericidal activities of the diverse molecular species of bile acid in humans and rodents is largely unknown. Here, we investigated the toxicity of 14 typical human and rodent free bile acids (FBAs) by monitoring intracellular pH, membrane integrity, and viability of a human intestinal bacterium, Bifidobacterium breve Japan Collection of Microorganisms (JCM) 1192T, upon exposure to these FBAs. Of all FBAs evaluated, deoxycholic acid (DCA) and chenodeoxycholic acid displayed the highest toxicities. Nine FBAs common to humans and rodents demonstrated that α-hydroxy-type bile acids are more toxic than their oxo-derivatives and β-hydroxy-type epimers. In five rodent-specific FBAs, β-muricholic acid and hyodeoxycholic acid showed comparable toxicities at a level close to DCA. Similar trends were observed for the membrane-damaging effects and bactericidal activities to Blautia coccoides JCM 1395T and Bacteroides thetaiotaomicron DSM 2079T, commonly represented in the human and rodent gut microbiota. These findings will help us to determine the fundamental properties of FBAs and better understand the role of FBAs in the regulation of gut microbiota composition.
Porphyromonas gingivalis is a low-abundance oral anaerobic bacterium implicated in periodontitis, a polymicrobial inflammatory disease, and the associated systemic conditions. However, the mechanism ...by which
P. gingivalis contributes to inflammation and disease has remained elusive. Here we show that
P. gingivalis, at very low colonization levels, triggers changes to the amount and composition of the oral commensal microbiota leading to inflammatory periodontal bone loss. The commensal microbiota and complement were both required for
P. gingivalis-induced bone loss, as germ-free mice or conventionally raised C3a and C5a receptor-deficient mice did not develop bone loss after inoculation with
P. gingivalis. These findings demonstrate that a single, low-abundance species can disrupt host-microbial homeostasis to cause inflammatory disease. The identification and targeting of similar low-abundance pathogens with community-wide impact may be important for treating inflammatory diseases of polymicrobial etiology.
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P. gingivalis induces changes to the amount and composition of the oral microbiota ►
P. gingivalis causes periodontitis in conventional but not germ-free mice ► Complement is also required for
P. gingivalis-induced periodontitis ► Defective leukocyte recruitment disrupts host-microbial homeostasis, causes bone loss
Calf diarrhea is associated with enteric infections, and also provokes the overuse of antibiotics. Therefore, proper treatment of diarrhea represents a therapeutic challenge in livestock production ...and public health concerns. Here, we describe the ability of a fecal microbiota transplantation (FMT), to ameliorate diarrhea and restore gut microbial composition in 57 growing calves. We conduct multi-omics analysis of 450 longitudinally collected fecal samples and find that FMT-induced alterations in the gut microbiota (an increase in the family Porphyromonadaceae) and metabolomic profile (a reduction in fecal amino acid concentration) strongly correlate with the remission of diarrhea. During the continuous follow-up study over 24 months, we find that FMT improves the growth performance of the cattle. This first FMT trial in ruminants suggest that FMT is capable of ameliorating diarrhea in pre-weaning calves with alterations in their gut microbiota, and that FMT may have a potential role in the improvement of growth performance.
Cyclin-dependent kinase 9 (CDK9), one crucial molecule in promoting the transition from transcription pausing to elongation, is a critical modulator of cell survival and death. However, the ...pathological function of CDK9 in bacterial inflammatory diseases has never been explored. CDK9 inhibition or knock-down attenuated Porphyromonas gingivalis-triggered inflammatory gene expression. Gene-expression microarray analysis of monocytes revealed that knock-down of CDK9 not only affected inflammatory responses, but also impacted cell death network, especially the receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase domain-like (MLKL)-mediated necroptosis after P. gingivalis infection. Inhibition of CDK9 significantly decreased necroptosis with downregulation of both MLKL and phosphorylated MLKL. By regulating caspase-8 and cellular FLICE inhibitory protein (cFLIP), key molecules in regulating cell survival and death, CDK9 affected not only the classic RIPK1-RIPK3-mediated necroptosis, but also the alternate TIR-domain-containing adapter-inducing interferon-β-RIPK3-mediated necroptosis. CDK9 inhibition dampened pro-inflammatory gene production in the acute infection process in the subcutaneous chamber model in vivo. Moreover, CDK9 inhibition contributed to the decreased periodontal bone loss and inflammatory response induced by P. gingivalis in the periodontal micro-environment. In conclusion, by modulating the RIPK3-MLKL-mediated necroptosis, CDK9 inhibition provided a novel mechanism to impact the progress of bacterial infection in the periodontal milieu.
Three difficult-to-cultivate, strictly anaerobic strains, AN20
, AN421
, and AN502, were analyzed within a project studying possible probiotics for newly hatched chickens. Phylogenetic analyses ...showed that strains AN20
, AN421
, and AN502 formed two well-separated phylogenetic lineages in all phylogenetic and phylogenomic trees comprising members of the family
. Comparison to reference genomes of type species Bacteroides fragilis NCTC 9343
, Phocaeicola abscessus CCUG 55929
, and Capsularis zoogleoformans ATCC 33285
showed low relatedness based on the calculated genome-to-genome distance and orthologous average nucleotide identity. Analysis of fatty acid profiles showed iso-C
, anteiso-C
, C
, C
, and iso-C
3OH as the major fatty acids for all three strains and additionally C
3OH for AN421
and AN502. A specific combination of respiratory quinones different from related taxa was found in analyzed strains, MK-5 plus MK-11 in strain AN20
and MK-5 plus MK-10 in strains AN421
and AN502. Strains AN421
and AN502 harbor complete CRISPR loci with CRISPR array, type II-C, accompanied by a set of
genes (
,
, and
) in close proximity. Interestingly, strain AN20
was found to harbor two copies of
gene with >95% similarity to
of B. fragilis, suggesting a horizontal gene transfer between these taxa. In summary, three isolates characterized in this study represent two novel species, which we proposed to be classified in two novel genera of the family
, for which the names
sp. nov. (AN20
= CCM 9041
= DSM 111154
) and
sp. nov. (AN421
= CCM 9040
= DSM 111155
) are proposed.
This study represents follow-up research on three difficult-to-cultivate anaerobic isolates originally isolated within a project focused on strains that are able to stably colonize newly hatched chickens, thus representing possible probiotics. This project is exceptional in that it successfully isolates several miscellaneous strains that required modified and richly supplemented anaerobic media, as information on many gut-colonizing bacteria is based predominantly on metagenomic studies. Superior colonization of newly hatched chickens by
spp.,
spp., or related taxa can be considered of importance for development of future probiotics. Although different experiments can also be performed with provisionally characterized isolates, precise taxonomical definition is necessary for subsequent broad communication. The aim of this study is therefore to thoroughly characterize these isolates that represent novel genera and precisely determine their taxonomic position among related taxa to facilitate further research and communication involving these strains.
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