Subgingival Prevalence and Antibiotic Susceptibility of Selenomonas noxia

Background <i>Selenomonas noxia</i> is a putative periodontal pathogen in subgingival biofilm communities. This study compared the subgingival prevalence and levels of <i>S. noxia</i> in those with severe periodontitis and those with periodontal health and assessed the in vitro antibiotic susceptibility of the species. Methods Subgingival biofilm samples from 206 adults with stage III (severe) periodontitis and 48 adults with periodontal health were examined with an <i>S. noxia</i>-specific whole chromosomal nucleic acid probe. Minimum inhibitory concentration (MIC) values of six antibiotics against <i>S. noxia</i> were determined in vitro with antibiotic gradient strips. Results <i>Selenomonas noxia</i> was more frequently detected in patients with severe periodontitis (53.4%) than persons with periodontal health (20.8%) (2.6-fold more frequent, p = 0.0001, Fisher's exact test). Heavy subgingival colonization by <i>S. noxia</i> (≥10⁶ cells/subject subgingival specimen) was also more frequent in persons with severe periodontitis (16.0%) than those with periodontal health (2.1%) (7.6-fold more frequent, p = 0.008, Fisher's exact test). <i>Selenomonas noxia</i> was susceptible in vitro to amoxicillin, azithromycin, clindamycin, doxycycline, and metronidazole (all MIC values ≤ 0.75 mg/L) but resistant to spiramycin (MIC > 32 mg/L). Conclusions <i>Selenomonas noxia</i> was significantly more prevalent at significantly higher subgingival levels in patients with severe periodontitis than adults with periodontal health. However, heavy <i>S. noxia</i> subgingival colonization was present in only a subset of severe periodontitis patients and rarely in those with periodontal health. <i>Selenomonas noxia</i> was susceptible in vitro to several antibiotics of potential therapeutic use in periodontitis therapy, with the exception of spiramycin. <i>Selenomonas noxia</i> may contribute to periodontitis in patients harboring high subgingival numbers of the organism.