Gut microbiota signatures associated with spermatogenic capacity and sperm retrieval outcomes in non-obstructive azoospermia

PURPOSE: To characterize gut microbiota composition in men with non-obstructive azoospermia (NOA) and evaluate associations with sperm retrieval outcomes following microdissection testicular sperm extraction (mTESE). METHODS: In this prospective cohort, fecal samples from 39 azoospermic men (obstructive azoospermia [OA], n = 14; NOA, n = 25) were analyzed. NOA patients were stratified into successful (NOA ( +)) and unsuccessful (NOA ( -)) sperm retrieval groups. Full-length 16S rRNA sequencing (PacBio) was performed. Microbial composition, diversity, and differential taxa were analyzed using QIIME2, DADA2, and linear discriminant analysis effect size (LEfSe). Receiver operating characteristic (ROC) analysis was used to assess the predictive performance of candidate markers. RESULTS: Compared with OA, NOA patients showed reduced Bacteroidota and increased Proteobacteria, indicating gut dysbiosis. Alpha diversity was similar between groups, whereas beta-dispersion revealed greater microbial variability in NOA. Within the NOA cohort, the NOA ( +) group exhibited a higher Firmicutes-to-Bacteroidota ratio and distinct microbial profiles. Finegoldia magna and other Firmicutes taxa were enriched in NOA ( +), whereas Bacteroidota-associated taxa predominated in NOA ( -). The Firmicutes-to-Bacteroidota ratio predicted successful retrieval with an area under the curve of 0.76, and Finegoldia magna abundance showed high specificity, although these findings were exploratory. CONCLUSION: Gut microbiota composition differs by azoospermia etiology and is associated with mTESE outcomes. Enrichment of Finegoldia magna and increased Firmicutes in NOA ( +) suggest a potential role of the gut-testis axis. Gut microbiota profiling may represent a non-invasive correlate of sperm retrieval success, although these exploratory findings require validation in larger independent cohorts.