Fimbrial production by Porphyromonas gingivalis was inactivated by insertion-duplication mutagenesis, using the cloned gene for the P. gingivalis major fimbrial subunit protein, fimA. by several criteria, this insertion mutation rendered P. gingivalis unable to produce fimbrilin or an intact fimbrial structure. A nonfimbriated mutant, DPG3, hemagglutinated sheep erythrocytes normally and was unimpaired in the ability to coaggregate with Streptococcus gordonii G9B. The cell surface hydrophobicity of DPG3 was also unaffected by the loss of fimbriae. However, DPG3 was significantly less able to bind to saliva-coated hydroxyapatite than wild-type P. gingivalis 381. This suggested that P. gingivalis fimbriae are important for adherence of the organism to saliva-coated oral surfaces. Further, DPG3 was significantly less able to cause periodontal bone loss in a gnotobiotic rat model of periodontal disease. These observations are consistent with other data suggesting that P. gingivalis fimbriae play an important role in the pathogenesis of human periodontal disease.

The subgingival microflora and serum antibody response was examined in Periodontitis patients with noninsulin‐dependent diabetes mellitus (NIDDM), impaired glucose tolerance (IGT), and normal glucose tolerance (NGT). The predominant cultivable microflora was determined for subgingival plaque sampled from two deep periodontal pockets in each of eight adult Periodontitis patients with NIDDM. Indirect immunofluorescence for Bactewides intermedius, Bacteroides gingivalis, and Haemophilus actinomycetemcomitans was used to examine these same samples as well as 186 additional subgingival plaque samples from 47 patients with moderate to severe generalized Periodontitis including 25 subjects with NIDDM, six subjects with IGT, and 16 subjects with NGT. Serum antibody levels to 13 microorganisms including seven oral bacterial species and one nonoral control species were measured by enzyme‐linked immunosorbent assays (ELISA) in 377 subjects including 84 normal subjects without periodontal disease, 112 normal subjects with Periodontitis, 19 periodontally normal subjects with IGT, 65 Periodontitis patients with IGT, 15 periodontally normal subjects with NIDDM, and 82 Periodontitis patients with NIDDM. Three hundred eighty‐two bacterial isolates were recovered from the eight patients. B. intermedius was the most frequently isolated microorganism constituting 16% of the total isolates followed by Wolinella recta and B. gingivalis, which each accounted for 13% of the total. Streptococcus sanguis was the most prevalent microorganism, which was found in 75% of the sites. Subgingival plaque samples examined by immunofluorescence demonstrate a high prevalence of black‐pigmented Bacteroides and suggest that the proportion of B. gingivalis but not B. intermedius is higher in NIDDM with Periodontitis than in other groups. Serological studies of B. gingivalis from patients with NIDDM indicate that these isolates comprise a serogroup distinct from those found in adult Periodontitis patients without diabetes. Serum IgG antibody levels were significantly elevated in nondiabetic, IGT, and NIDDM patients with Periodontitis toward both B. gingivalis strains tested. Nondiabetic Periodontitis patients had significantly elevated levels of serum IgG toward B. intermedius strain 9336 while Periodontitis patients with IGT had significantly elevated antibody levels to B. intermedius strain 25261. Microbiologic and immunologic data from the present study suggests that B. intermedius. W. recta, and B. gingivalis are important in the etiology of Periodontitis in adult patients with NIDDM.

Oral infection of rats with Streptococcus mutans mutant 805 was used to prevent the establishment of its highly virulent wild-type progenitor NCTC 10449S. The dose of wild-type cells required to colonize 100% of the specific pathogen-free Osborne-Mendel rats (21 to 43 days old) consuming caries test diet 2000 was greater than 4 x 10(5) but less than 4 x 10(6) cells. Therefore, the latter dose was used to challenge rats which had already been colonized by an oral dose of about 6 x 10(8) cells of mutant 805. This prior infection by 805 either completely protected rats from subsequent colonization by wild-type cells or greatly delayed and diminished their emergence. Rats in which wild-type cells became established showed much lower percentages of wild-type cells in their total recoverable floras than did rats that were not first infected by the mutant. Large doses of mutant 805, however, did not displace wild-type cells from rats once it became established. There was no evidence of reversion of the mutant, which is defective in intracellular polysaccharide synthesis and hence is less virulent than wild-type cells. The data indicate that the S. mutans cell which first colonizes rats gains the strongest ecological position and is difficult to displace. Also, they suggest the possible prophylactic utility of infection by this mutant of S. mutans.