New breakthrough in infertility research! Semen, intestinal flora imbalance is related to male infertility

In addition to the common causes of male infertility, varicocele, obstructive azoospermia, sexual dysfunction, congenital absence of testicles, testicular dysplasia and other sperm problems, there are many infertility that cannot be detected. This type of infertility for which no cause can be detected is called idiopathic male infertility.

What causes idiopathic male infertility?

Recently, a study conducted by the Cleveland Clinic Urology Department at Eur Urol for the first time comprehensively investigated the microbial composition of idiopathic infertile men. This study analyzed the resident microbial populations of bacteria in the intestines, semen, and urine of sterile and fertile men. The results of the study indicate that the imbalance of the intestinal and semen microbiota is related to idiopathic male infertility.

In the study, the researchers recruited 25 idiopathic infertile men and 12 fertile healthy men, and collected their rectal swabs, semen samples, and mid-section urine samples to conduct a comprehensive microbial community analysis.

Semen and urine flora are similar, but very different from intestinal flora

Since little is currently known about the interaction between gut microbes and the microbiome of the genitourinary system, the researchers first analyzed the composition of the participants' rectal, urine, and semen microbial communities.

Researchers found through 16S rRNA gene analysis:

Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria are the four main bacterial phyla in the intestine and genitourinary system;

Surprisingly, the microbiota of urine and semen are very similar;

The microbiome in the gut is significantly different from the microbiome in urine and semen

The relative abundance of different flora in the rectum, semen and urine

Then the researchers analyzed the a-diversity and b-diversity of microorganisms in the intestines, urine and semen. It is found that the microbial a-diversity of the intestine is significantly higher than that of urine and semen, and its b-diversity is different from that of urine and semen. However, the abundance of Gardnerella and Corynebacterium in semen and urine is higher than in the intestine.

Although the microbiota of urine and semen are very similar, there are still differences. Compared with urine, the abundance of Pseudomonas, Pseudoxanthomonas and Acidovorax in semen is higher than that in urine, while the abundance of Veillonella and General Prevotella is less abundant than urine.

The difference between the bacteria in urine (yellow) and semen (blue)

Increased semen balloon bacteria in infertile men

Low semen viscosity

Knowing the difference between the intestinal, urine and semen microbiota, what is the difference between the microbiota of infertile and fertile men?

Researchers found that semen samples of infertile men showed significant a-diversity.

Then, the researchers began to further analyze the abundance of the microbial flora and found that:

Semen flora: Aerococcus (Aerococcus) in the semen of infertile men increased, while Collinsella decreased. Collinsella is very important for sperm quality. When the vas deferens is removed, Collinsella is depleted.

Rectal flora: The abundance of Anaerococcus (Anaerococcus) in the rectum of infertile men decreased, while the abundance of Lachnospiraceae, Collinsella and Coprococcus increased.

Urine flora: On the contrary, the urine of infertile men contains more anaerobic bacteria.

Rectal and semen microbiome disorders are linked to infertility

So why is the abundance of the same flora so different between fertile and infertile men? In order to better understand the relationship between specific flora and clinical phenotypes, the researchers conducted a generalized linear regression model analysis and found that:

There is a significant inverse relationship between the abundance of Aerococcus and leukocytospermia and the viscosity of semen.

The more balloon bacteria in the semen, the lower the viscosity of the semen. Too low semen viscosity will result in low sperm activity, resulting in a low pregnancy rate. So in the previous experiment, the researchers found that in the semen of infertile men, balloon bacteria increased.

The abundance of Prevotella is negatively related to semen quality and directly related to BMI

The abundance of Pseudomonas is directly related to the total active sperm count, but is inversely proportional to the semen pH.

Pseudomonas is positively correlated with sperm count, and Prevot bacteria is negatively related to sperm quality, so this also verifies the previous findings: Pseudomonas in semen is higher than urine, and Prevot bacteria abundance Lower than urine.

The microbiota of infertile men, the yellow mark is related to fertility, and the blue mark is the group of bacteria related to infertility

In summary, this preliminary study comprehensively investigated the male infertility microbiota for the first time. It was found that the semen alpha-diversity of infertile men increased, the semen balloon bacteria increased, and the rectal anaerobes decreased. The research results may help doctors diagnose and treat male infertility based on the microbiome in the future.

Perhaps in the future, when checking for infertility factors, in addition to conventional methods, testing and analysis of intestinal and semen flora will also be arranged.