Male Infertility and the Seminal Fluid Microbiota

Weng SL, Chiu CM, Lin FM, et al. Bacterial communities in semen from men of infertile couples: metagenomic sequencing reveals relationships of seminal microbiota to semen quality. PLoS One. 2014;9(10):e110152. 

Retrospective cohort of semen samples undergoing bioinformatics analysis

Ninety-six semen samples were collected at the reproductive center of Mackay Memorial Hospital, Taipei, Taiwan, Republic of China, from men who had been diagnosed with primary infertility for at least 1 year. Also included in the study were semen samples from 36 fertile men. All participants were between the ages of 26 and 58 years and had no other significant health problems. 

Semen samples were collected, analyzed for bacterial communities, and evaluated for semen quality by measuring semen volume, sperm concentration, strict morphology, atypical forms, and leukocytes. Computer-assisted semen analysis (CASA) was also performed. Semen was collected by masturbation into a sterile cup after 3 to 5 days of abstinence.

Of the 96 samples, the most common flora found in the seminal fluids were Lactobacillus (19.9%), Pseudomonas (9.85%), Prevotella (8.51%), and Gardnerella (4.21%). It was discovered that bacterial communities in semen are clustered into 3 main groups (G1-G3). G1 was characterized by the mother genus Pseudomonas and included bacteria from the Bacillus, Pelomonas, Rhondanobacter, Enterobacter, Klebsiella, Brevibacillus, and Orchrobactrum genera. G2 was characterized by mother genus Lactobacillus and included bacteria from the Enterobacter, Klebsiella, Pseudomonas, Stenotrophomonas, Bacillus, Delftia, Chryseobacterium, Brevibacillus, and Ochrobactrum genera. G3 was characterized by the mother genus Prevotella and also included bacteria from the Pedobacter, Propionibacterium, Dietzia, and Halomonas genera. 

 

Normal samples had significantly higher levels of Lactobacillus and Gardnerella, while samples deemed to be of low quality were higher in Prevotella. Of note, 80.6% of normal semen samples were clustered in the Lactobacillus group (G2). Comparative analysis demonstrates that samples in the G1 and G3 groups had a 5.2-fold and 8.5-fold greater chance of containing 2 abnormal semen parameters compared to samples in the G2 group. According to CASA, morphology was the only semen parameter strongly associated with pathogenic bacteria. 

Infertility, or failure for a couple to conceive after 12 months of unprotected intercourse, affects 15% of all couples, and nearly 50% of these cases are attributed to male factor infertility. There is evidence to suggest that male fertility has been diminishing by 2% per year in the last several decades, with an estimated decline in mean sperm count of approximately 0.94x106 per mL per year.^1,2 Hormonal imbalances, oxidative stress, endocrine disruptors, genitourinary tract infections, and poor lifestyle choices can all play a role in male infertility. Infections of the prostate, epididymis, and testicles play a causative role in 15% of male factor infertility.^3,4 Seminal bacteria and leukocytes impair fertility by impairing spermatogenesis and reducing sperm function. 

The composition of the human microbiome impacts health and can contribute to disease.^5,6 A previous study by Ibadin and Ibeh using culture method demonstrated that 41.4% of infertile men had at least 1 of the following bacteria: Staphylococcus aureus (16.9%), Staphylococcus saprophyticus (9.2%), Escherichia coli (6.9%), Proteus mirabilis (3.4%), Klebsiella spp (2.3%), Pseudomonas aerouginosa (1.1%), and Proteus vulgaris (2.3%). They were identified in semen samples with abnormal total motility and morphology.⁷ De Fransesco et al performed culture studies on 696 semen samples, finding that sperm concentration, motility, and morphology were most likely to be abnormal in the presence of Gardnerella vaginalis and Ureaplasma urealyticum.⁸ Most previous studies identified seminal bacteria using culture or polymerase chain reaction‒based methods. 

 

The authors of this study aim to improve the understanding of seminal bacterial communities by presenting an analysis flow using next-generation sequencing technology coupled with clinical semen analysis. The most abundant genera found in this study support the findings made by Hou et al, who also compared seminal microbiota in fertile and infertile men using a different method of pyrosequencing of bacterial ribosomal ribonucleic acid.⁹ Based on their findings, the authors of this study believe that supplementation with Lactobacillus could help support a healthy microbiome in the seminal fluids, thereby maximizing fertility potential. Larger, follow-up studies are warranted to validate this opinion and to further elucidate the mechanism by which pathogenic bacteria cause infertility.