The association of depression and oral microbiota

The intestinal microbiota has been implicated in depression, and patients with periodontal disease show particularly high rates of depressive symptoms. This study explored the relationship between oral microbiota, depression severity, and systemic inflammatory factors. Thirty-two patients with depression were enrolled and divided into mild (n = 13; PHQ-9 ≤ 14) and major (n = 19; PHQ-9 > 14) depression groups. Significant differences in oral microbial diversity were found between groups. Alpha-diversity was higher in mild depression (Shannon, P = 0.01; Simpson, P = 0.03), although richness did not differ significantly (Chao1, P = 0.06; ACE, P = 0.06). Beta-diversity analysis revealed distinct microbial community structures (Unweighted UniFrac, P < 0.01; Weighted UniFrac, P < 0.01). Several bacterial taxa (e.g., Actinobacteria, Micrococcales, Micrococcaceae, Peptostreptococcaceae, Flavobacteriaceae, Rothia, Paraclostridium, Capnocytophaga, Haemophilus_parainfluenzae, and Neisseria_elongata) showed positive correlations with depression severity. In contrast, Xanthomonadales was negatively associated. No significant intergroup differences were observed in inflammatory factors. These findings suggest that oral microbiota composition and diversity are closely linked to depression severity, though the role of inflammatory factors remains unclear.