Relationship of periodontal bacterium genotypic variations with periodontitis in type 2 diabetic patients.

P eriodontitis is characterized by gingival inflammation, as well as loss of connective tissue and bone from around the roots of the teeth, which leads to eventual tooth exfoliation. Severe periodontitis often coexists with diabetes and is considered to be the sixth complication of the disease, as both type 1 and type 2 diabetic patients show a threeto fourfold increased risk of periodontitis (1– 4). However, the involved factors and mechanisms are still unclear. Periodontitis is caused by a small subset of periodontal Gram-negative bacteria that attach to the gingival margin, such as Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Tannerella forsythia, Treponema denticola, and Prevotella intermedia (5). Among them, P. gingivalis is considered to be a bona fide periodontal pathogen (5–7). P. gingivalis fimbriae are hair-like appendages on the bacterial surface that mediate bacterial interactions with and invasion of host tissues (8). These fimbriae have been classified into six types (I through V and Ib), based on the diversity of the fimA genes encoding FimA (a subunit protein of fimbriae) (9,10). Studies have shown that clones with type II fimA have a significantly greater virulence in vitro and in vivo (10– 12). Therefore, specific P. gingivalis fimA types may be related to periodontitis associated with type 2 diabetes.