Oropharyngeal microbiota in patients with psychotic disorders: A scoping review on compositional and functional...

Oropharyngeal microbiota may be implicated in the onset and progression of psychotic disorders. This scoping review aims to map the existing evidence concerning the composition, diversity, and metabolic pathways of the oropharyngeal microbiota in patients aged 18 to 65 with a main diagnosis of a psychotic disorder, including individuals at clinical high-risk for psychosis (CHRP) or experiencing first episode psychosis (FEP).

The scoping review was performed according to the PRISMA-ScR checklist. The systematic literature search was conducted using PubMed, Web of Science, and CINAHL until February 2024.

Seven cross-sectional studies were included, comprising 43 individuals at CHRP, 13 with FEP, 85 with first-episode of schizophrenia (FES), 171 with schizophrenia, and 8 with another schizophrenia spectrum disorder. The oropharyngeal microbiota showed an increase in Lactobacillus gasseri abundance in schizophrenia, and in Firmicutes/Proteobacteria phylum ratio in patients experiencing CHR-P and FES. In schizophrenia, an altered β-diversity was observed alongside increased metabolic pathways related to metabolite transporters. In FES, higher α-diversity and disruptions in amino acid, carbohydrate, and xenobiotic metabolism pathways were found. Hydrogen sulfide (H₂S)-producing bacteria were generally enriched in all the stages of disease. Correlations were observed between oropharyngeal microbiota and psychotic symptom domains.

Potential microbial signatures, such as Lactobacillus gasseri and H₂S-producing bacteria, were identified in the oropharyngeal microbiota. Alterations in the oropharyngeal microbiota composition and function may be associated with different stages of psychotic disorders, with some overlap between CHR-P and FES.