Fig. 1.

P. gingivalis-mediated periodontitis is a biofilm associated disease of slow progression. Early within the oral cavity there is a mixed community of bacteria with an abundance of Gram-positive organisms (purple cocci). Over time (represented by the triangle at bottom), there is a maturation of the biofilm. External and internal pressures such as an anoxic environment, mammalian cell infiltrate, viral and phage activity, DNA exchange, nutrient availability, and physical and chemical interactions of the microbes, drive development. A currently unidentified event occurs that allows for the out-growth of Gram-negative organisms (red and green rods), in particular P. gingivalis (shown in green). There is also active recruitment of cells of the immune system, such as neutrophils (shown in purple) to the site, which then brings in a battery of host-derived signaling molecules, impacting the microbial community.