(Coykendall et al. 1980) Shah and Collins 1988
It is found in the oral cavity, where it is implicated in certain forms of periodontal disease, as well as the upper gastrointestinal tract, respiratory tract, and in the colon. Collagen degradation observed in chronic periodontal disease results in part from the collagenase enzymes of this species. It has been shown in an in vitro study that P. gingivalis can invade human gingival fibroblasts and can survive in them in the presence of considerable concentrations of antibiotics. P. gingivalis also invades gingival epithelial cells in high numbers, in which cases both bacteria and epithelial cells survive for extended periods of time. High levels of specific antibodies can be detected in patients harboring P. gingivalis.
In addition, P. gingivalis has been linked to rheumatoid arthritis. It contains the enzyme peptidyl-arginine deiminase, which is involved in citrullination. Patients with rheumatoid arthritis have an increased incidence of periodontal disease and antibodies against the bacterium are significantly more common in these patients.
Arg-gingipains have been found to play a key role in the collection of nutrients for P. gingivalis survival. Rgp degrades large peptides of the host organism to provide the bacterium with an abundant nitrogen and carbon source from human albumin serum. P. gingivalis can also degrade transferrin within host cells which provides the organism with an abundant iron source needed to perform multiple cellular functions.
The gingipains are also responsible for a number of necessary functions related to host invasion and colonization. Rgp gingipains are necessary for adhesion and invasion as they processed precursor proteins of long fimbriae. The P. gingivalis genes encoding RgpA, Kgp, and hemagglutinin A (HagA) were strongly expressed after incubation with T. denticola. The hemagglutinin adhesion domain-containing proteins act to increase adhesive capacities of P. gingivalis with other bacterial species.  They are also associated with coordinating the integrity of the biofilm in the developing and maturation phase. Lys- gingipains (Kgp) can bind to immobilized matrix proteins fibrinogen and fibronectin and may have a role in host colonization.
Gingipains also have the ability to degrade multiple signals of the host immune response. They have the ability to cleave subclass 1 and 3 IgG antibodies  as well as proinflammatory cytokines such as IL-1β, IL-2, IL-6, TNF-α and IL-8 in regions of high P. gingivalis concentration., which impairs host immune response function. Rgp can inhibit IL-2 accumulation in T-cells, which enables it to evade the host adaptive immune response, by modulating T-cell communication and proliferation.
Gingipains are key factors in tissue damage symptoms of periodontitis, which results from the degradation of matrix metalloproteins, collagen, and fibronectin. Degradation of these substrates interferes with interactions between host cells and the extracellular matrix, therefore impeding wound healing and causing destruction of periodontal tissues. Rgp is responsible for eliciting the host inflammatory response via the p38α MAPK transduction pathway. This response likely contributes to the inflammatory nature of periodontitis and is involved in tissue and bone destruction.
The encapsulated strain of P. gingivalis is much more virulent than the nonencapsulated strain in a mouse abscess model. The capsule is a capsular polysaccharide and when present down regulates cytokine production especially proinflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α, indicating host evasion responses. However, other studies have found the CPS to elicit host immune responses like PMN migration and dose and time dependent expression of cell migration chemokines like MCP-1, KC, MIP-2 and RANTES in CPS-challenged murine peritoneal macrophages. These conditions are likely to contribute to the inflammatory lesions observed in periodontitis.
Vaccines made from P. gingivalis CPS apparently impair oral bone loss in murine models. These vaccines have been able to elicit potent immune responses such as increased IgM and IgG responses that recognize whole P. gingivalis organisms.
Fimbriae are appendages involved in cellular attachment and greatly contribute to virulence. and are found on many Gram-negative and some Gram-positive bacteria.
P. gingivalis virulence is heavily associated with fimbriae as they have been characterized to be key factors in adhesion, invasion, and colonization. Fimbriae are also responsible for invasion of membrane vesicles into host cells. They were found to bind to cellular α5β1 integrins, which mediated adherence and impaired the homeostatic controls of host cells. Fimbriae were also found to be associated with modulating β2 integrin adhesive activity for uptake by monocytes using the CD14/TLR2/PI3K signaling complex, which may contribute to intracellular evasion tactics by P. gingivalis. P. gingivalis has long fimbriae, short fimbriae, and accessory components, each of which have distinct functions.
Long fimbriae (FimA), also known as major fimbriae, are long, peritrichous, filamentous components. They have a role in initial attachment and organization of biofilms, as they act as adhesins that mediate invasion and colonization of host cells contributing to P. gingivalis virulence.
Short fimbriae (Mfa1), also known as minor fimbriae, have distinct roles from long fimbriae and are characterized to be essential for cell-cell auto aggregation and recruitment for microcolony formation. Short fimbriae are involved in cell-cell adhesion with other dental commensals. It was found to coadhere and develop biofilm in conjunction with Streptococcus gordonii by interaction with SspB streptococcal surface polypeptide. This interaction may be essential in the invasion of dentinal tubules by P. gingivalis.
Fim C,D, and E accessory components associate with the main FimA protein and have a role in binding with matrix proteins and interaction with CXC-chemokine receptor 4. Loss of function experiments have confirmed that P. gingivalis mutants deficient for Fim C, D, or E have drastically attenuated virulence.
Evasion of host defenses and immune responses
P. gingivalis has many ways of evading host immune responses which affects its virulence. It does this by using a combination of gingipain proteases, a capsular polysaccharide, induction of host cell proliferation, and the cleavage of chemokines responsible for neutrophil recruitment.
Virulent P. gingivalis further modulates leukocyte recruitment by proteolysis of cytokines and chemokines that are secreted by the host cells. The arg-gingipain and lys-gingipains are responsible for this proteolysis. In a study using a mouse model, P. gingivalis was specifically found to down-regulate IL-8 induction, causing delayed neutrophil recruitment. Prevention of neutrophil recruitment may inhibit the clearance of the bacterium from the site of infection allowing for colonization.P. gingivalis is able to evade opsonophagocytosis from PMN’s by using Gingipain K (Kgp) to cleave IgG 1 and 3. This further modulates immune response by impairing signaling. Other studies have found that P. gingivalis can subvert the complement pathway through C5αR and C3αR, which modulates the killing capacity of leukocytes, allowing for uncontrolled bacterial growth. P. gingivalis was also found to inhibit pro inflammatory and antimicrobial responses in human monocytes and mouse macrophages by fimbrial binding to CXCR4, inducing PKA signaling and inhibiting TLR-2-mediated immune response.
Once in the host cells, P. gingivalis is capable of inhibiting apoptosis by modulating the JAK/Stat pathway that controls mitochondrial apoptotic pathways. A proliferative phenotype maybe beneficial to the bacterium as it provides nutrients, impairs host cell signaling, and compromises the integrity of the epithelial cell layer, allowing for invasion and colonization.
P. gingivalis is a “red” bacterium and a “keystone” bacterium in the onset of chronic adult periodontitis. Though it is found in low abundance in the oral cavity, it causes a microbial shift of the oral cavity, allowing for uncontrolled growth of the commensal microbial community. This leads to periodontitis through the disruption of the host tissue homeostasis and adaptive immune response. After using using laser capture microdissection plus qRT-PCR to detect P. gingivalis in human biopsies, colocalization of P. gingivalis with CD4+ T cells was observed.  However, the infection mechanism of T cells by P. gingivalis remains unknown.
P. gingivalis has been associated with increasing the virulence of other commensal bacterium in both in vivo and in vitro experiments. P. gingivalis outer membrane vesicles were found to be necessary for the invasion of epithelial cells of Tannerella forsythia. P. gingivalis short fimbriae were found to be necessary for coculture biofilm formation with Streptococcus gordonii  Interproximal and horizontal alveolar bone loss in mouse models are seen in coinfections involving P. gingivalis and Treponema denticola. The role of P. gingivalis as a community activist in periodontitis is seen in specific pathogen-free mouse models of periodontal infections. In these models, P. gingivalis inoculation causes significant bone loss, which is a significant characteristic of the disease. In contrast, germ free mice inoculated with a P. gingivalis monoinfection causes no bone loss, indicating P. gingivalis alone cannot induce periodontitis 
- Naito M, Hirakawa H, Yamashita A, et al (August 2008). "Determination of the Genome Sequence of Porphyromonas gingivalis Strain ATCC 33277 and Genomic Comparison with Strain W83 Revealed Extensive Genome Rearrangements in P. gingivalis". DNA Res. 15 (4): 215–25. doi:10.1093/dnares/dsn013. PMC 2575886. PMID 18524787.
- Wegner, N., Wait, R., Sroka, A., Eick, S., Nguyen, K.-A., Lundberg, K., Kinloch, A., Culshaw, S., Potempa, J. and Venables, P. J. (September 2010). "Peptidylarginine deiminase from Porphyromonas gingivalis citrullinates human fibrinogen and α-enolase: Implications for autoimmunity in rheumatoid arthritis". Arthritis Rheum. 62 (9): 2662–2672. doi:10.1002/art.27552.
- Ogrendik M, Kokino S, Ozdemir F, Bird PS, Hamlet S (2005). "Serum Antibodies to Oral Anaerobic Bacteria in Patients With Rheumatoid Arthritis". MedGenMed 7 (2): 2. PMC 1681585. PMID 16369381.
- American Academy of Periodontology 2010 In-Service Exam, question A-85
- Sheets, S; Robles-Price, A.; Mckenzie, R. (2012). "Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis". Front Biosci. 13: 3215–3238. PMC 3403687. PMID 18508429.
- Grenier, D; Imbeault, S; Plamondon, P.; Grenier, G.; Nakayama, K.; Mayrand, D. (2001). "Role of gingipains in growth of Porphyromonas gingivalis in the presence of human serum albumin". Infect Immun 69 (8): 5166–5172. doi:10.1128/IAI.69.8.5166-5172.2001. PMC 98614. PMID 11447200.
- Furuta, N; Takeuchi, H.; Amano, A (2009). "Entry of Porphyromonas gingivalis outer membrane vesicles into epithelial cells causes cellular functional impairment". Infect Immun 77 (11): 4761–70. doi:10.1128/IAI.00841-09. PMC 2772519. PMID 19737899.
- Meuric V, Martin B, Guyodo H, Rouillon A, Tamanai-Shacoori Z, Barloy-Hubler F, Bonnaure-Mallet M (2013). "Treponema denticola improves adhesive capacities of Porphyromonas gingivalis". Mol Oral Microbiol 28 (1): 40-53.
- Kubinowa, M; Hasagawa, Y.; Mao, S (2008). "P. gingivalis accelerates gingivial epithelial cell progression through the cell cycle". Microbes Infect 10 (2): 122–128. doi:10.1016/j.micinf.2007.10.011. PMC 2311419. PMID 18280195.
- McAlister, A.D.; Sroka, A; Fitzpatrick, R. E; Quinsey, N.S, Travis, J.; Potempa, J; Pike, R.N (2009). "Gingipain enzymes from Porphyromonas gingivalis preferentially bind immobilized extracellular proteins: a mechanism favouring colonization?". J. Periodontal Res 44 (3): 348–53. doi:10.1111/j.1600-0765.2008.01128.x. PMC 2718433. PMID 18973544.
- Vincents, Bjarne; Guentsch, A; Kostolowska, D; von Pawel-Rammingen, U; Eick, S; Potempa, J; Abrahamson, M (October 2011). "Cleavage of IgG1 and IgG3 by gingipain K from Porphyromonas gingivalis may compromise host defense in progressive periodontitis". FASEB 25 (10): 3741–3750. doi:10.1096/fj.11-187799.
- Grenier, D; Tanabe, S (2010). "Porphyromonas gingivalis Gingipains Trigger a Proinflammatory Response in Human Monocyte-derived Macrophages Through the p38alpha Mitogen-activated Protein Kinase Signal Transduction Pathway". Toxins (Basel) 2 (3): 341–52. doi:10.3390/toxins2030341.
- Khalaf, Hazem; Bengtsson; Bengtsson, T (2012). "Altered T-Cell Responses by the Periodontal Pathogen Porphyromonas gingivalis". In Das, Gobardhan. PLoS One 7 (9): 45192. Bibcode:2012PLoSO...745192K. doi:10.1371/journal.pone.0045192.
- Singh, A; Wyant, T; et al (2011). "The capsule of Porphyromonas gingivalis leads to a reduction in the host inflammatory response, evasion of phagocytosis, and increase in virulence". Infect Immun 79 (11): 4533–4542. doi:10.1128/IAI.05016-11. PMC 3257911. PMID 21911459.
- D'Empaire, G; Baer, M.T; et al (2006). "The K1 serotype capsular polysaccharide of Porphyromonas gingivalis elicits chemokine production from murine macrophages that facilitates cell migration". Infect Immun 74 (11): 6236–43. doi:10.1128/IAI.00519-06. PMC 1695525. PMID 16940143.
- Gonzalez, D; Tzianabos, A.O.; et al (2003). "Immunization with Porphyromonas gingivalis Capsular Polysaccharide Prevents P. gingivalis-Elicited Oral Bone Loss in a Murine Model". Infection and Immunity 71 (4): 2283–2287. doi:10.1128/IAI.71.4.2283-2287.2003. PMC 152101. PMID 12654858.
- Tsuda, K; Amano, A; et al (2005). "Molecular dissection of internalization of Porphyromonas gingivalis by cells using fluorescent beads coated with bacterial membrane vesicle". Cell Struct Funct. 30 (2): 81–91. doi:10.1247/csf.30.81. PMID 16428861.
- Hajishengallis, G; Wang, M.; et al (2006). "Porphyromonas gingivalis fimbriae proactively modulate beta2 integrin adhesive activity and promote binding to and internalization by macrophages". Infect. Immun. 74 (10): 5658–5666. doi:10.1128/IAI.00784-06. PMC 1594907. PMID 16988241.
- Lin, X; Wu, J.; et al (2006). "Porphyromonas gingivalis minor fimbriae are required for cell-cell interactions". Infect Immun 74 (10): 6011–6015. doi:10.1128/IAI.00797-06. PMC 1594877. PMID 16988281.
- Park, Y; Simionato, M et al (2005). "Short fimbriae of Porphyromonas gingivalis and their role in coadhesion with Streptococcus gordonii". Infect Immun 73 (7): 3983–9. doi:10.1128/IAI.73.7.3983-3989.2005. PMC 1168573. PMID 15972485.
- Love, R; McMillan, M. et al (2000). "Coinvasion of Dentinal Tubules byPorphyromonas gingivalis and Streptococcus gordonii Depends upon Binding Specificity of Streptococcal Antigen I/II Adhesin". Infect. Immun. 68 (3): 1359–65. doi:10.1128/IAI.68.3.1359-1365.2000. PMC 97289. PMID 10678948.
- Pierce, D.L; Nishiyama, S. et al (2009). "Host adhesive activities and virulence of novel fimbrial proteins of Porphyromonas gingivalis". Infect. Immun. 77 (8): 3294–301. doi:10.1128/IAI.00262-09. PMC 2715668. PMID 19506009.
- Hajishengallis, G; Liang, S. et al (2011). "A Low-Abundance Biofilm Species Orchestrats Inflammatory Periodontal Disease through the Commensal Microbiota and the Complement Pathway". Cell Host Microbe 10 (5): 497–506. doi:10.1016/j.chom.2011.10.006. PMC 3221781. PMID 22036469.
- Wang, M; Liang S. et al (2009). "Differential virulence and innate immune interactions of Type I and II fimbrial genotypes of Porphyromonas gingivalis". Microbiol. Immunol 24 (6).
- Liang, S; Krauss, J.L. et al (2011). "The C5a receptor impairs IL-12-dependent clearance of Porphyromonas gingivalis and is required for induction of periodontal bone loss". J. Immunol. 186 (2): 869–77. doi:10.4049/jimmunol.1003252. PMC 3075594. PMID 21149611.
- Hajishengallis, G; Wang, M. et al (2008). "Pathogen induction of CXCR4/TLR2 cross-talk impairs host defense function". Proc Natl Acad Sci U S A 105 (36): 13532–7. Bibcode:2008PNAS..10513532H. doi:10.1073/pnas.0803852105. PMC 2533224. PMID 18765807.
- Mao, S; Park, Y. et al (2007). "Intrinsic apoptotic pathways of gingival epithelial cells modulated by Porphyromonas gingivalis". Cell Microbiol 9 (8): 1997–2007. doi:10.1111/j.1462-5822.2007.00931.x. PMC 2886729. PMID 17419719.
- Kubinowa, M; Yoshiaki, H. et al (2008). "P. gingivalis accelerates gingivial epithelial cell progression through the cell cycle". Microbes Infection 10 (2).
- Hajishengallis, G (2009). "Porphyromonas gingivalis-host interactions: open war or intelligent guerilla tactics?". Microbes Infect. 11 (6–7): 637–645. doi:10.1016/j.micinf.2009.03.009. PMC 2704251. PMID 19348960.
- Darveau, R.P.; Hajishengallis, G. et al (2012). "Porphyromonas gingivalis as a potential community activist for disease". J. Dent. Res. 91 (9): 816–820. doi:10.1177/0022034512453589. PMC 3420389. PMID 22772362.
- Guyodo H, Meuric V, Le Pottier L, Martin B, Faili A, Pers JO, Bonnaure-Mallet M (2012). "Colocalization of Porphyromonas gingivalis with CD4+ T cells in periodontal disease". FEMS Immunol Med Microbiol 64 (2): 175-183.
- Inagaki, S; Onishi, S. et al (2006). "Porphyromonas gingivalis vesicles enhance attachment, and the leucine-rich repeat BspA protein is required for invasion of epithelial cells by "Tannerella forsythia"". Infect. Immun. 74 (9): 5023–8. doi:10.1128/IAI.00062-06. PMC 1594857. PMID 16926393.
- Verma, R.K.; Rajapakse, S. et al (2010). "Porphyromonas gingivalis and Treponema denticola Mixed Microbial Infection in a Rat Model of Periodontal Disease". Interdiscip. Perspect. Infect. Dis.