Changes in the stool and oropharyngeal microbiome in obsessive-compulsive disorderOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This case-control study compared the gut (stool) and oropharyngeal (throat and tonsil) microbiomes of people with obsessive-compulsive disorder against healthy controls. The researchers used 16S rRNA gene sequencing of the V3-V4 region. They measured alpha and beta diversity and used LEfSe and Wilcoxon tests to find bacteria that differed between groups. Stool and throat samples were collected from patients before and after three months of pharmacological and cognitive behavioral treatment, to also test whether therapy shifted the microbiome.
Who was studied?
Participants were 32 adult OCD patients and matched healthy controls recruited in Barcelona, Spain. Patients were diagnosed by psychiatrists using DSM-IV criteria at Bellvitge Hospital. The recruited OCD group was mostly women, with a mean age near 40 years. Controls came from the same sociodemographic environment and were screened to exclude any psychiatric disorder. Samples were taken at two time points, before and after treatment. Psychotic disorders, substance abuse, and autism spectrum disorder were exclusion criteria. Sequencing yielded 96 stool and 96 oropharyngeal samples.
What were the most important findings?
OCD stool showed only a trend toward lower alpha diversity, not significant after correction (adjusted p = 0.057). The Bacteroidetes to Firmicutes ratio did not differ between groups. OCD gut samples had increased Rikenellaceae, particularly the genus Alistipes, a taxon associated with gut inflammation. They had decreased Coprococcus, a genus linked to synthesis of the dopamine metabolite DOPAC, plus lower Prevotellaceae. Depletion of Coprococcus correlated with obsession severity. In the throat, OCD cases had a lower Fusobacteria to Actinobacteria ratio. Treatment did not significantly change the microbiome (T0 vs T3).
What are the greatest implications of this study?
The results add to evidence that gut and oral microbiome imbalances accompany OCD, possibly involving inflammation from higher Alistipes and altered dopamine signaling from lower Coprococcus. This points to the microbiome as a candidate target for future study. The authors stress causation cannot be established. The brain can shape the gut through the gut-brain axis, so changes could be a cause or a consequence of OCD or its anxiety. The sample was small, adult-only, and exploratory, so larger longitudinal and interventional studies are needed before any clinical use.