SOME men have low fertility because of microorganisms lurking in their semen, say researchers in Hungary. They have shown that bacteria can prevent sperm from swimming well enough to reach an egg.
The reproductive systems of up to two-thirds of men are infected with anaerobic bacteria such as Fusobacterium nucleatum and Bacteroides fragilis. These infections usually go unnoticed unless extremely large numbers of the bacteria are present, when they can cause pain and discharge.
Bela Molnar of Albert Szent-Gysrgyi Medical University in Szeged wondered if these bacteria could be one factor in some men's fertility problems. So his team isolated F. nucleatum and B. fragilis from 43 infected men and incubated sperm of normal motility with various concentrations of the bacteria. These ranged from concentrations comparable to a mild case without symptoms to a dose equivalent to a raging infection.
Sperm will swim in a culture medium for a day or more. But even in the samples with low concentrations of bacteria, only 1 per cent of the sperm were still moving after 18 hours. At the highest dose, they all stopped moving after 3 hours.
Molnar says that the bacteria may inhibit sperm motility in several ways: by competing for fructose, a sugar that sperm need for energy; by producing products that are toxic to sperm; or by physically interfering with the lashing of sperm tails.
If infertile men have asymptomatic infections, Molnar thinks they should be given broad-spectrum antibiotics for three months to eliminate the bacteria, before beginning IVF. "We should first treat them and let them try to conceive the normal way," he says.
New Scientist issue 17th October.
Author: Mitzi Baker
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