Filifactor alocis: The Newly Discovered Kid on the Block with Special Talents

Abstract

Infection-induced periodontal disease has been primarily focused on a small group of periodontal pathogens. A paradigm shift, based on data emerging from the oral microbiome project, now suggests the involvement of as-yet-unculturable and fastidious organisms. Collectively, these studies have demonstrated that there are changes in the periodontal status associated with shifts in the composition of the bacterial community in the periodontal pocket. In addition, it is likely that the emerging new pathogens may play a more significant role in the disease. One of the organisms previously unrecognized is Filifactor alocis. While this Gram-positive anaerobic rod has been identified in peri-implantitis, in endodontic infections, and in patients with localized aggressive periodontitis, its presence is now observed at significantly higher levels in patients with adult periodontitis or refractory periodontitis. Its colonization properties and its potential virulence attributes support the proposal that F. alocis should be included as a diagnostic indicator of periodontal disease. Moreover, these emerging characteristics would be consistent with the polymicrobial synergy and dysbiosis (PSD) periodontal pathogenesis model. Here, unique characteristics of F. alocis are discussed. F. alocis has specific factors that can modulate multiple changes in the microbial community and host cell proteome. It is likely that such variations at the molecular level are responsible for the functional changes required to mediate the pathogenic process.

Keywords: community dynamics; host interaction; oxidative stress; periodontitis; polymicrobial infection; proteomics.

Figure 1.

F. alocis – surface morphology. (A) Transmission electron micrograph showing F. alocis, a Gram-positive, asaccharolytic, obligate anaerobic rod. (B) Transmission electron micrograph of F. alocis showing membrane and cell wall structures. (C) Scanning electron micrograph of F. alocis showing surface punctations resembling minor projections.

Figure 2.

F. alocis as an oxidative sink. Community dynamics may play an important role in microbial survival in an oxidative stress environment of the periodontal pocket. The high abundance of F. alocis in the periodontal pocket may be consistent with the relative resistance to oxidative stress and its enhanced growth under those conditions. The beneficial relationships via the interactions with other microbes in the biofilm would stabilize the heterotypic community, including protection from the host immune response. Tissue damage observed in periodontal disease is a combination of bacterial-induced and host-mediated damage (see text for details).

Figure 3.

Epithelial cell interaction of F. alocis during mono and co-culture with P. gingivalis. (A) F. alocis–infected epithelial cells. The bacteria adhere to the eukaryotic cell, causing surface variations (green arrows showing adhesion of F. alocis). (B) F. alocis–infected epithelial cells showing surface variations of filamentous projections noted during co-culture with P. gingivalis strains. Orange arrows = filamentous projections; green arrows = F. alocis; blue arrows = P. gingivalis.

Figure 4.

Pathogenic properties of F. alocis (see text for details).