Microbiota of the seminal fluid

22 01 2014

To the Editor:

I read with great interest the article by Hou et al. (1) regarding the microbiota of the seminal fluid from sperm donors and infertile subjects. This study aimed to explore potential causes of male infertility and showed that increased number of bacteria were present in semen samples from infertile subjects as well as sperm donors. The topic of infections and infertility is extremely interesting, and there are still a lot of aspects to be covered.

The significance of bacteriospermia in subfertile men is controversial. When dealing with a sperm sample the possibility of contamination is always probable since the presence of normal flora cannot be overlooked. Moreover, it is quite challenging to evaluate which microorganisms significantly affect male fertility potential. However, bacteriospermia and leukocytospermia have a negative effect on male fertility through multiple proposed mechanisms (2). In the largest study to evaluate bacteriospermia, Domes et al. (2) commonly diagnosed in subfertile men bacteriospermia and leukocytospermia, which were associated with a significantly increased DNA fragmentation index.

It is universally accepted that the male reproductive tract is not sterile. However, in my opinion, it’s quite unusual for most of the donor sperm samples (28/30) to harbor such an increased number of bacteria that outnumbers sperm concentration, as seen on the Gram stained preparations. The question remains if a donor with bacteriospermia can be fertile and, more important, if such a donor can be used in fertility treatments. As very elegantly pointed out by the authors there is always the possibility of sharing certain bacterial populations with the female partner and thus probably interfering even more with their reproductive function. A properly designed randomized controlled trial could add the needed data to better define the importance of bacteriospermia and the utility, if any, of treating these patients with antimicrobials in an effort to improve their sperm parameters and their fertility treatment outcome.

Stavroula Baka, M.D., University of Athens, Athens, Greece


1. Hou D, Zhou X, Zhong X, Settles M, Herring J, Wang L, et al. Microbiota of the seminal fluid from healthy and infertile men. Fertil Steril 2013;100:1261-9.

2. Domes T, Lo KC, Grober ED, Mullen JBM, Mazzulli T, Jarvi K. The incidence and effect of bacteriospermia and elevated seminal leukocytes on seminal parameters. Fertil Steril 2012;97:1050-5.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2014.01.042

The authors respond:

We welcome the comments of Dr. Stavroula Baka on our findings that were reported in “Microbiota of the seminal fluid from healthy and infertile men” (1) and agree that further research is warranted to understand whether any of the bacterial populations found in semen from healthy men can adversely affect male fertility potential.

In our study we found there were high numbers of diverse kinds of bacteria present in most samples of both sperm donors and infertility patients. The species composition of bacterial communities varied widely among subjects, but they could be clustered into six groups based on similarities in composition and the rank abundances of taxa. Dr. Baka remarked that in his opinion it was quite unusual for most of the donor sperm samples (28/30) to have high numbers of bacteria that outnumber sperm. In previous studies methods that require culturing of bacteria have been used to characterize bacteria of seminal fluid and these are limited because many species of bacteria are recalcitrant to cultivation. However, in our study we used molecular methods based on the phylogenetic classification of 16S rRNA gene sequences recovered from semen samples, and this obviates the need to cultivate the bacteria present in samples. This methodology is increasingly used in studies of the human microbiome because it overcomes the inherent limitations of cultivation-dependent methods and provides a more complete and comprehensive understanding of microbial diversity. Many of the bacterial populations we observed in semen samples are strict anaerobes that are likely difficult to culture without special efforts, and we suspect this accounts for why they have been overlooked in the past.

We have no reason to suspect that donors were infected or that semen samples were contaminated during the process of collection and storage. Semen donors satisfied a series of enrollment criteria that included a physical examination and sperm function tests that were done to exclude individuals with disease or subfertile subjects. Moreover, semen samples were collected according to established protocols that reduce the possibility of contamination.

Dr. Baka suggested that perhaps in the future studies might be done to determine whether treating these patients with antimicrobials might improve sperm parameters and improve the outcomes of fertility treatments. Perhaps this is so, but we hasten to point out that the bacteria present may well be commensal populations that have no adverse consequences. We also caution that using antibiotics in semen before assisted reproductive technology treatment may damage sperm and even the quality of the embryo. However, as Dr. Baka points out, many questions remain unanswered. Perhaps none is more intriguing than whether bacterial populations are being shared between heterosexual partners and how this might affect the risk to disease in males and females.

Larry J. Forney, Ph.D., Director, Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho
Chen Xu, M.D., Ph.D., Professor and Director, Department of Histology and Embryology, Shanghai Key Laboratory of Reproductive Medicine, Shanghai Jiao Tong University School of Medicine, People’s Republic of China
Dongsheng Hou, M.D. Ph.D., Shandong Provincial Hospital, Shandong University, People’s Republic of China


1. Hou D, Zhou X, Zhong X, Settles M, Herring J, Wang L, et al. Microbiota of the seminal fluid from healthy and infertile men. Fertil Steril 2013;100:1261-9.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2014.01.043




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