Clinical and microbiological features of refractory periodontitis subjects

The purpose of this investigation was to compare the clinical parameters and the site prevalence and levels of 40 subgingival species in successfully treated and refractory periodontitis subjects. 94 subjects received scaling and root planing and if needed, periodontal surgery and systemically administered tetracycline. 28 refractory subjects showed mean full mouth attachment loss and/or > 3 sites showing attachment loss > 2.5 mm within 1 year post-therapy. 66 successfully treated subjects showed mean attachment level gain and no sites with attachment loss > 2.5 mm. Baseline subgingival plaque samples were taken from the mesial aspect of each tooth and the presence and levels of 40 subgingival taxa were determined using whole genomic DNA probes and checkerboard DNA-DNA hybridization. The mean levels and % of sites colonized by each species (prevalence) was computed for each subject and differences between groups sought using the Mann-Whitney test. Most of the 40 species tested, including Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Treponema denticola and Bacteroides forsythus, were equally or less prevalent in the refractory group. Prevotella nigrescens was significantly more prevalent in successfully treated subjects, while refractory subjects harbored a larger proportion of Streptococcus species, particularly Streptococcus constellatus. The odds of a subject being refractory was 8.6 (p < 0.001) if S. constellatus constituted > or = 3.5% of the total DNA probe count. Since few microbiological differences existed between treatment outcome groups using DNA probes to known species, the predominant cultivable microbiota of 33 subgingival samples from 14 refractory subjects was examined. 85% of the 1649 isolates were identified using probes to 69 recognized subgingival species. The remaining unidentified strains were classified by analyzing 16S rRNA gene sequences. Many sequenced isolates were of taxa not considered a common part of the oral microbiota such as Acinetobacter baumanni, Gemella haemolysans, Enterococcus faecalis, Staphylococcus warneri, Pseudomonas aeruginosa and novel species in the genera Bartonella, Ralstonia, Neisseria, Eubacterium, Rothia, Gordona, Gemella, Corynebacterium, Leptotrichia, and Actinomyces. Refractory subjects constituted a heterogeneous group based on their subgingival microbiota. As a group, they did not harbor more of the "classic" periodontopathogens, although elevated proportions of S. constellatus were found.