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BACKGROUND: Previous studies have shown differences in the mean proportions of subgingival species in samples from periodontitis subjects in different countries, which may relate to differences in diet, genetics, disease susceptibility and manifestation. The purpose of the present investigation was to determine whether there were differences in the subgingival microbiotas of Swedish and American subjects who exhibited periodontal health or minimal periodontal disease.

METHOD: One hundred and fifty eight periodontally healthy or minimally diseased subjects (N Sweden=79; USA=79) were recruited. Subjects were measured at baseline for plaque, gingivitis, BOP, suppuration, pocket depth and attachment level at 6 sites per tooth. Subgingival plaque samples taken from the mesial aspect of each tooth at baseline were individually analyzed, in one laboratory, for their content of 40 bacterial species using checkerboard DNA-DNA hybridization (total samples=4345). % DNA probe counts comprised by each species was determined for each site and averaged across sites in each subject. Significance of differences in proportions of each species between countries was determined using ancova adjusting for age, mean pocket depth, gender and smoking status. p values were adjusted for multiple comparisons. Cluster analysis was performed to group subjects based on their subgingival microbial profiles using a chord coefficient and an average unweighted linkage sort.

RESULTS: On average, all species were detected in samples from subjects in both countries. After adjusting for multiple comparisons, 5 species were in significantly higher adjusted mean percentages in Swedish than American subjects: Actinomyces naeslundii genospecies 1 (9.7, 3.3); Streptococcus sanguis (2.5, 1.2); Eikenella corrodens (1.7, 1.0); Tannerella forsythensis (3.5, 2.3) and Prevotella melaninogenica (6.3, 1.8). Leptotrichia buccalis was in significantly higher adjusted mean percentages in American (5.5) than Swedish subjects (3.0). Cluster analysis grouped 121 subjects into 8 microbial profiles. Twenty four of the 40 test species examined differed significantly among cluster groups. Five clusters were dominated by American subjects and 2 clusters by Swedish subjects. Fifty eight of 79 (73%) of the Swedish subjects fell into 1 cluster group dominated by high proportions of A. naeslundii genospecies 1, Prevotella nigrescens, T. forsythensis and P. melaninogenica. Other clusters were characterized by high proportions of Actinomyces gerencseriae, Veillonella parvula, Capnocytophaga gingivalis, Prevotella intermedia, Eubacterium saburreum, L. buccalis and Neisseria mucosa.

CONCLUSIONS: The microbial profiles of subgingival plaque samples from Swedish and American subjects who exhibited periodontal health or minimal disease differed. The heterogeneity in subgingival microbial profiles was more pronounced in the American subjects, possibly because of greater genetic and microbiologic diversity in the American subjects sampled.