Much of the evidence linking periodontal disease and diabetes mellitus can be found in an interesting microbiological study of the Pima Indians of the Gila River Indian Community of Arizona. This particular group of people has the highest recorded incidence and prevalence of diabetes mellitus. Over 40 percent of the Pima population over 35 years of age has diabetes mellitus that is mostly Type 2 DM.

The microbiologic data from the study of adult periodontitis in Pima patients with Type 2 DM suggest that Bacteroides intermedius, Wolinella recta, and Bacteroides gingivalis, the three most predominant isolates in the subgingival dental plaque of these patients, are important in the etiology of periodontitis in adult patients with Type 2 DM. Additionally, Bacteroides species have been reported to be significant pathogens in the etiology of extraoral infections in adult diabetes, including infections of the endopelvic fascia and gangrene.