Testicular microbiome in azoospermic men-first evidence of the impact of an altered microenvironment.

Study Question: Given the relevant role of the extracellular microenvironment in regulating tissue homeostasis, is testicular bacterial microbiome (BM) associated with germ cell aplasia in idiopathic non-obstructive azoospermia (iNOA)?
Summary Answer: A steady increase of dysbiosis was observed among testis with normal spermatogenesis vs. iNOA with positive sperm retrieval and iNOA with complete germ cell aplasia.
What Is Known Already: Tissue-associated BM has been reported to be a biologically important extracellular microenvironment component for numerous body habitats, but not yet for the human testis.
Study Design, Size, Duration: Cross-sectional study, investigating tissue-associated BM in the testis of (i) five men with iNOA and negative sperm retrieval at microdissection testicular sperm extraction (microTESE); (ii) five men with iNOA and positive sperm retrieval at microTESE; and (iii) five normozoospermic men upon orchiectomy. Every testicular specimen was histologically classified and analyzed in terms of bacterial community.
Participants/materials, Setting, Methods: Massive ultra-deep pyrosequencing was applied to investigate testis microbiome. Metagenome was analyzed using Quantitative Insights Into Microbial Ecology (QIIME). Tissue-associated bacterial load was quantified by digital droplet PCR.
Main Results and the Role of Chance: Normozoospermic men showed small amounts of bacteria in the testis, with Actinobacteria, Bacteroidetes, Firmicutes Proteobacteria as the dominating phyla; iNOA individuals had increased amounts of bacterial DNA (P = 0.02), associated with decreased taxa richness due to the lack of Bacteroidetes and Proteobacteria (P = 2 × 10-5). Specimens with negative sperm retrieval at microTESE depicted complete germ cell aplasia and a further decrease in terms of Firmicutes and Clostridia (P < 0.05), a complete lack of Peptoniphilus asaccharolyticus, but increased amount of Actinobacteria.
Limitations, Reasons for Caution: The limited number of specimens analyzed in this preliminary study deserves external validation. The paraneoplastic microenvironment could have an impact on the residential bacterial flora.
Wider Implication of the Findings: Human testicular microenvironment is not microbiologically sterile, containing low amounts of Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. A dysbiotic bacterial community was associated with iNOA and complete germ cell aplasia. Novel findings on testicular BM could support future translational therapies of male-factor infertility.
Study Funding/competing Interest(s): This work was supported by URI-Urological Research Institute free funds. Authors declared no conflict of interest.
Trial Registration Number: N/A.