Association of Bacteroides forsythus and a novel Bacteroides phylotype with periodontitis

Abstract

Chronic periodontitis is a common infectious disease in the adult population. The etiology is clearly bacterial, and a small number of bacterial species have been consistently associated with periodontitis, including Bacteroides forsythus and Porphyromonas gingivalis. Comparatively little attention has been paid to the identification of health-associated and potentially beneficial bacterial species that may reside in the gingival sulcus. The purpose of the present study was to examine the relationship of the presence of B. forsythus and a newly identified Bacteroides phylotype, oral clone BU063, to periodontal health status. The study was accomplished with a set of samples that were collected from subjects with periodontitis and healthy controls. These samples had previously been analyzed for the presence of P. gingivalis. An oral sampling strategy that included every tooth and a PCR-based detection method were used to maximize detection sensitivity. The presence of B. forsythus in the oral cavity was strongly associated with periodontitis, and its nearest genetic neighbor, oral clone BU063, was associated with oral health (P < 0.0001 for both). Colonization with P. gingivalis was independent of the presence of either Bacteroides species, but the two Bacteroides species were found together less often than would be expected by chance (P < 0.0001). This suggests the presence of a specific exclusionary mechanism between the two Bacteroides species. Comparisons between these two organisms may prove useful for studies that determine how B. forsythus functions in the disease process. In addition, oral clone BU063 deserves further study as a possible preventive or therapeutic intervention for periodontitis.

FIG. 1.

PCR amplification of ISR rDNAs of B. forsythus and oral clone BU063. The lane labeled “Bf” contains DNA amplified from B. forsythus strain ATCC 43037, and the last lane labeled with a minus sign contains a negative (no-template) control. The B. forsythus DNA template yielded a fragment of 1.61 kb, and oral clone BU063 yielded a fragment of 1.48 kb. Lanes 1 through 5 contain DNA amplified from clinical samples; lane 2 was scored as positive for B. forsythus, and lanes 1, 3, and 5 were scored as positive for BU063.

FIG. 2.

Schematic diagram of the rDNA ISR between the 16S and 23S rRNA genes for B. forsythus and oral clone BU063. Genes are shown as boxes, and noncoding regions are shown as lines. The same tRNA genes are present in both organisms, but noncoding regions differ in both size and sequence.

FIG. 3.

Prevalence of B. forsythus, P. gingivalis, and oral clone BU063, a newly identifed phylotype closely related to B. forsythus, in subjects with periodontitis and healthy subjects. Actual percentages are shown inside the bars. The data for P. gingivalis have been reported previously (5). The total sample size was 293 subjects, with samples obtained from 121 subjects with periodontitis (▪) and 172 healthy, age-matched controls (□). Differences in the prevalences of all three species in orally healthy individuals and individuals with periodontitis were significant by chi-square analysis (P < 0.0001).