Introduction. The study of the human microbiome has become of increasing scientific interest. A balanced and diverse microbiota of the male re- productive system is essential for optimal reproductive health. Today, there are no diagnostic tests to determine the effect of specific microorganisms on the quality of seminal fluid, however, the use of next-generation sequencing (NGS), using the 16S rRNA gene sequence as a molecular marker, provides us with the opportunity to understand the complexity of the relationship between the microbiome and its host.

The aim of the study. To conduct a comparative analysis of the taxonomic structure of the microbiota between patients with obstructive and nonobstructive azoospermia and the fertility group (patients with a history of having children).

Materials and methods. The study included (n=57) patients (infertile patients with obstructive azoospermia (OA), non-obstructive azoospermia (NOA) and a control group (FERT). All patients underwent percutaneous aspiration of sperm from the testicle (testicular sperm aspiration, MESA), with subsequent in vitro fertilization using ICSI technology, or cryopreservation of biological material. The amplicons of the bacterial 16S rRNA gene were analyzed using high-performance next-generation sequencing (NGS). For this research of bacterial composition of the urogenital tract and control the purity of the method, samples has been taken from the urethra of each patient who underwent testicular biopsy. The data was processed using the QUICKTIME program (version 1.9.1).

Results. No significant differences were found in the comparison groups during the study of the urethral bacterial composition. The species diversity, as well as the total number of detected taxonomic units (OTE) in the NOA and OA groups are significantly lower than in the FERT group. The presentation of the phylum like Proteobacteria, Firmicutes, Bacteroidetes, Bifidobacterium adolescentis in the studied groups is different. Three microorganisms were identified with the same frequency in the urethra and testicular tissue (the exact Fisher criterion was used, adjusted for multiple comparison by the Benjamin-Hochberg method). The representation of the phylum Prevotella, Comamonadaceae, Veillonella dispa, Comamonadaceae in the studied groups differs.

Conclusion. Testicular tissue is not sterile and has its own unique microbial landscape for each comparison group. Bacterial communities of testicular tissue in patients with azoospermia are characterized by a reduced diversity and a specific composition that differs from the urethral microbiota. These results may be useful in further to study the role of microbiota in the pathology of spermatogenesis and developing new approaches to the treatment and diagnosis of male infertility.