Subgingival microbial profiles in refractory periodontal disease

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Abstract
The purpose of the present investigation was to examine subgingival microbial profiles associated with refractory periodontitis and to seek such profiles in periodontally healthy, periodontally well-maintained elder and untreated periodontitis subjects. 36 subjects were defined as refractory on the basis of further attachment loss after scaling and root planing, surgery and systemically administered antibiotics. A total of 890 subgingival plaque samples (mean/subject=24.7) were taken from the mesial aspect of each tooth in each subject at baseline and individually processed for their content of 40 subgingival taxa using checkerboard DNA-DNA hybridization. Cluster analysis was performed on mean within subject species counts using the chord coefficient and an average unweighted linkage sort. Significant differences among clusters for individual and complexes of species were sought using the Kruskal Wallis test. The microbial profiles of the refractory subjects were compared with those of 27 periodontally healthy subjects (n plaque samples=708), 35 periodontally well-maintained elder subjects (n plaque samples=801) and 115 untreated adult periodontitis subjects (n plaque samples=2871). 28 of 36 refractory subjects fell into 4 clusters with >29% similarity. 10 of 40 species and 4 of 7 complexes differed significantly among clusters. Profile (Cluster) I (n=4) was characterized by high proportions of "yellow" and "green" complex species, profile II (n=3) by low total counts and high proportions of "orange" and "purple" complex species, profile III (n=9) by high total counts and counts of Actinomyces and "purple" complex species, profile IV (n=12) by high proportions of "red" and "orange" complex species. The mean profiles of each cluster were subjected to cluster analysis with microbial data from 4380 (mean 24.7) baseline subgingival plaque samples from 27 periodontally healthy, 35 treated, well-maintained elders and 115 untreated adult periodontitis subjects. 12 clusters were formed with >41% similarity. 3 of the refractory profiles were detected in 3 cluster groups. Profile II in a cluster of 1 healthy, 1 elder and 4 untreated periodontitis subjects; profile III in a cluster of 1 healthy, 2 elder and 12 periodontitis subjects; Profile IV, with 1 healthy and 5 untreated periodontitis subjects. The profile not detected in non refractory subjects was dominated by Streptococcus species. 9 clusters did not harbor refractory profiles. 11.1% of healthy, 8.6% of elder and 18.3% of periodontitis subjects were in clusters exhibiting refractory microbial profiles. 4 subgingival microbial profiles were detected among refractory subjects. "Refractory microbial profiles" could be detected in subjects who had not yet exhibited refractory disease.