Table 3.

Studies on the relationships between gut microbiota and schizophrenia (SZ).

Authors and Year	Type of Study	Methods	Findings
Zheng et al., 2019 [160]	Cross-sectional study; animal study	Comparing gut microbiota between 63 treated and untreated SZ patients and 69 HCs; GF mice received SZ FMT	-Both treated and untreated SZ subjects showed altered microbiota and decreased microbiome heterogeneity than HC; -SZ severity was correlated with unique bacterial taxa; -GF mice receiving SZ FMT showed lower glutamate and higher glutamine and GABA in the hippocampus and displayed SZ-relevant behaviours
Shen et al., 2018 [161]	Cross-sectional study	Comparing gut microbiota between 64 SZ patients and 53 HC using 16S rRNA sequencing	-Increassed Proteobacteria, Succinivibrio, Megasphaera, Collinsella, Clostridium, Klebsiella and Methanobrevibacter in SZ; -Decreassed Blautia, Coprococcus and Roseburia in SZ; -Proposed microbiota-based diagnosis for SZ
Yuan et al., 2018 [162]	Cross-sectional study	Comparing gut microbiota between 41 first-episode SZ patients and 41 HCs; testing 24-week risperidone treatment effects	-Altered microbiota composition in patients, modulated by risperidone treatment
Li et al., 2021 [171]	Cross-sectional study	Investigating faecal microbiota differences between 38 SZ patients and 38 HC, as well as exploring whether such differences were associated with brain structure and function, through 16S rRNA sequencing, sMRI and rs-fMRI	-SZ showed increassed Veillonella, decreased Ruminococcus, Roseburia, GMV and ReHo; increased amplitudes of low-frequency fluctuation, -Both GMV and ReHo were related to the diversity of gut microbiota

Legend: GABA—gamma-aminobutyric acid; GF—germ-free; GMV—gray matter volume; HC—healthy controls; FMT—faecal microbiota transplant; ReHo—regional homogeneity; rs-fMRI—resting-state functional magnetic resonance imaging; sMRI—structural magnetic resonance imaging.