A taxon-centered review of bacterial shifts in psychiatric disorders.

Background: Psychiatric conditions rank among the leading causes of disability worldwide, with their burden steadily increasing in recent years. Recent research highlights the gut-brain axis as a pivotal pathway in mental health, implicating gut microbiota shifts in conditions such as depression, anxiety, schizophrenia, bipolar disorder, autism spectrum disorder, Alzheimer's disease and others. However, most reviews remain diagnosis-centered. Methods: We conducted a structured literature review of articles published between January 2015 and July 2025 in PubMed, Scopus, and Web of Science. We included both human and animal studies that reported taxonomic changes in gut microbiota associated with psychiatric or neurodevelopmental disorders. Editorials, conference abstracts, and studies lacking full-text availability, not addressing psychiatric outcomes or specific taxonomic data were excluded. Thus, data on bacterial taxa reported as increased or decreased versus controls were extracted and reorganized into a taxon-centered database. Results: The analysis suggested distinct yet overlapping microbial alterations across psychiatric conditions. Taxa such as Conclusion: By changing the perspective from diagnosis to taxon-centered analysis, this review suggests microbial signatures that appear across psychiatric diseases, supporting the possibility of shared pathophysiological pathways. Given the largely associative nature of the available data, these findings should be interpreted cautiously and may help guide future research exploring the role of the gut microbiota in mental health.