Semen microbiome linked to sperm abnormalities

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by Dr Semyon Bodian

Semen microbiome composition has been associated with sperm abnormalities, in a study of men in the United States.

Scientists from the University of California, Los Angeles (UCLA) were able to correlate the levels of different bacteria in semen with both sperm motility and concentration. Little research has investigated the links between the semen microbiome and resulting sperm abnormalities and, thus, potential effects on male fertility. Meanwhile there has been focus on the vaginal microbiome and its impact on reproductive and neonatal outcomes.

'There is much more to explore regarding the microbiome and its connection to male infertility. However, these findings provide valuable insights that can lead us in the right direction for a deeper understanding of this correlation' said Dr Vadim Osadchiy, study lead author and resident in the Department of Urology at UCLA, California.

Two genera of bacteria whose levels correlated to sperm abnormalities were identified. Semen with higher levels of Lactobacillus iners were linked with abnormally lower levels of sperm motility. Three species from the Pseudomonas genus, P. flourescens, P. stutzeri and P. putida, were linked to sperm concentration. Semen with higher levels of P. fluorescens and P. stutzeri were associated with abnormally lower sperm concentration. However, such concentrations were also associated with lower quantities of P. putida.

A potential link between L. iners and lower sperm motility may result from the bacteria's production of the L-lactic acid isomer, which is associated with increased inflammation of the local environment. The study's authors were keen to underline that these findings do not indicate causation of infertility or sperm abnormalities and are purely observations which could aid in the understanding of the mechanisms of infertility and sperm abnormalities.

The study, published in Scientific Reports, examined the semen from 73 men who were receiving consultation for either fertility treatment or vasectomies, with the latter having proven biological paternity. The subjects' semen was analysed using both a calibrated automated semen analyser and a high-powered microscopy. DNA was extracted from the semen, amplified and then sequenced to study the sperms' ribosomal RNA.

Results were adjusted for age, BMI, circumcision status, smoking, and alcohol intake history, but the study was limited by the limited range of socioeconomic status of the study participants, sourced from the same geographical location. In addition, antibiotic use or treatment for genitourinary infections was not accounted for, as was neither information regarding the participant's sexual behaviour nor the use or mode of contraception. A man's semen microbiome could be affected through different sexual activities and interactions with other bodily microbiomes, such as the urethra.

'Our research aligns with evidence from smaller studies and will pave the way for future, more comprehensive investigations to unravel the complex relationship between the semen microbiome and fertility,' said Dr Osadchiy.

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