The relationship between seminal microbiome and male reproductive wellness: a systematic review†

The seminal microbiome, which is composed of different types of bacteria in semen and seminal plasma, has a significant impact on male reproductive health by changing the quality of semen and fertility. Previously regarded as sterile, the male reproductive tract contains microbes originating from the gastrointestinal tract, reproductive organs, and external sources such as sexual partners. Dysbiosis alters sperm parameters, triggers inflammation and oxidative stress, and is associated with conditions such as infertility, HPV infection, prostatitis, prostate cancer, and azoospermia. This systematic review adhered to the PRISMA 2020 guidelines (with 2025 extensions for reproducibility) and examined studies from PubMed, Scopus, and Science Direct (2015-2025, with prior context), concentrating on human, in vitro, and rodent models. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes are among the most important phyla. Beneficial genera, such as Lactobacillus, improve sperm motility, concentration, and DNA integrity, whereas dysbiotic taxa, such as Prevotella, Pseudomonas, and Ureaplasma, are associated with declines. Sexual activity facilitates bidirectional microbial transfer, modifying diversity and fostering the dysbiosis. Inflammatory cytokines, reactive oxygen species, and metabolic disruptions are all involved in this process. Changes that are specific to a disease, such as higher levels of Fusobacterium in HPV-positive samples, worsen the situation. This review highlights how the microbiome alters sperm function and causes infertility. Standardized methods and long-term studies are needed to prove causality. Probiotics and other therapeutic interventions show promise in restoring balance and boosting fertility.