Many people undergoing fertility treatment face the disappointment of unexplained failure. Recent research indicates that semen can harbour high levels of bacteria that reduce the function, and fertility of individual sperm, suggesting it is crucial to test for and treat bacterial infection in sperm before undergoing fertility treatment.  

Now, Mohamad Eid Hammadeh and co-workers at the University of Saarland in Germany, along with Mohammed Hamad at King Saud Bin Abdulaziz University for Health Sciences in Saudi Arabia, have shown that bacteriospermia appears to play a key role in the failure of a reproductive therapy called intracytoplasmic sperm injection (ICSI). 

ICIS involves injecting a single sperm into a mature egg, and if a viable embryo is generated, it is then transferred into the uterus. However, the sperm used must have the correct ratio of two proteins, protamines P1 and P2, to provide tight packing for sperm DNA. Otherwise DNA can fragment, leading to poor embryo quality. The ability of sperm to move independently (sperm motility) also impacts on overall sperm quality.  

Hammadeh and his team enrolled 84 couples due to undergo ICIS treatment at the University of Saarland infertility clinic. They collected semen samples from every male participant and analysed features including sperm bacterial content, protamine levels, DNA integrity, and sperm motility.  

They found that 34.5 percent of samples were infected with at least one type of bacteria at concentrations high enough to have an impact on sperm quality. The bacteria present in samples included three species of Staphylococcus, along with Escherichia coli, Enterococcus faecalis and Streptococcus. Alongside reduced sperm quality, the bacteriospermia samples had imbalanced protamine levels compared with non-infected males. This was reflected in significant differences in fertilization rates following ICIS treatment.  

In total, 34 out of 84 females became pregnant after the ICIS course. The team found that infected males who had higher P1 levels than P2 in their sperm were less likely to make females pregnant. Their results suggest protamine balance is a vital part of male fertility.  

Precisely how bacteria influence sperm composition and concentration is not clear, but Hammadeh’s team believe it may be connected with increases in inflammation and reactive oxygen species triggered by the immune system in response to infection.  

“Male partner patients should do a semen bacterial investigation and then treat the bacteriospermia before the patients undergo ICSI treatment,” state the authors in their paper published in Reproductive Biology. They add that more research on this issue is necessary.

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