Harmful bacteria in semen could be new cause of male infertility

A potential new cause of male infertility has been found – harmful bacteria in semen. And it could be easily treated with antibiotics. When men have certain kinds of bacteria in their semen, their partner is less likely to get pregnant, early-stage Danish research has found. The study involved couples who were either having fertility treatment or who had repeated miscarriages – but the bacteria may lower fertility for all couples, said the researchers. Shorts When couples are struggling to get pregnant, there can be many potential causes. In men, possible explanations include low sperm counts or blockages in the tubes that carry sperm from the testes, caused by sexually transmitted diseases (STDs) like chlamydia. But the three types of bacteria implicated in the latest research – Gardnerella, Fannyhessea and Prevotella – are not classed as STDs. They are normally found either in the gut or in small amounts in the vagina. Yet they are not “good bacteria” in the vagina. Most beneficial vaginal bacteria are a type called Lactobacillus, which create acidic conditions that stop the growth of harmful bacteria and fungi. Women who have fewer Lactobacilli and more of the three bacteria found by this study have lower chances of getting pregnant, previous studies have suggested. And it may also cause an infection called bacterial vaginosis or BV. The latest study, published in The Lancet Obstetrics, Gynaecology, and Women’s Health, suggests these bad bacteria could have a home somewhere within the man’s reproductive system and could be reinfecting his partner during sex. The researchers analysed bacteria from semen, vaginal samples and the gut in 353 women and 191 of their male partners who were either having fertility treatments like IVF or were at a clinic for recurrent miscarriages. About two-thirds of the men had no bacteria in their semen. “Probably the most healthy state would be that there are no bacteria,” said Dr Kilian Vomstein, an obstetrician at Copenhagen University Hospital, who was involved in the research. In those having fertility treatment, if the man had the bad bacteria, 57 per cent of their partners went on to have a baby in the next year, compared with 85 per cent of the rest of the group. In those who had recurrent miscarriages, if the man had the bad bacteria, 75 per cent went on to have a successful pregnancy over the next four years, compared with 95 per cent of the others. “It is quite a dramatic impact,” said Professor Henriette Nielsen, also an obstetrician at Copenhagen University Hospital. Explanations for impact on fertility Possible explanations include that the bacteria are harming sperm, or that they are being passed on to the woman and making her womb somehow less receptive to an embryo. But regardless of the cause, treating infected men with antibiotics could help improve a couple’s chance of conceiving, said Dr Vomstein. A trial last year in women with BV found that they are more likely to stay uninfected if their male partner also had antibiotics at the same time. Professor Channa Jayasena, a male fertility expert at Imperial College London who was not involved in the study, said while the research was at an early stage, the results were surprising. “Unfortunately, the gut microbiome [via faeces] does interact with with the reproductive microbiomes of the female or male, which could be accounting for some cases of subfertility. “It could be that the male is passing on problems to the female, or vice versa. But the value of the study is actually raising this really elegantly as a concept.” Kevin McEleny, chair of the British Fertility Society, said that more research was need to confirm the results, and that doctors do not yet know which bacteria are present in semen when couples have no trouble conceiving. “We really need to know what’s normal before we say what’s abnormal,” he said.