Originally published on Stuff, 03 July 2023
Dr Siouxsie Wiles MNZM is an award-winning microbiologist and science communicator at the University of Auckland.
OPINION: My ears always prick up when I hear about a new study that shows bacteria or viruses might be doing something new or unexpected. I’m a microbiologist; I can’t help myself!
The latest study to pique my interest was just published in the journal Science Translational Medicine. In a nutshell, the team led by Professor Yutaka Kondo and Dr Ayako Muraoka give some compelling evidence that a type of bacteria commonly found in the mouth and gut could be involved in the development of endometriosis.
If this turns out to be correct, it could completely revolutionise the way this devastating condition is treated.
So, what is endometriosis? It’s a condition where cells from the lining of the uterus – the endometrium – grow outside the uterus. Depending on where those cells grow, and how much, people can experience a wide range of symptoms including debilitating pain, abnormal menstrual bleeding, painful intercourse, fertility issues and even bowel problems like bloating, constipation and diarrhoea. It’s these last symptoms that often lead to people with endometriosis being misdiagnosed as having irritable bowel syndrome instead. Endometriosis is very common – about one in 10 girls, women and people assigned female at birth have it.
Kondo, Muraoka and colleagues took advantage of a dataset made public several years ago by researchers studying the bacteria living in the reproductive tracts of 110 Chinese women.
They reanalysed the data, specifically looking for bacteria that were more likely to be found in the women in the dataset who were known to have endometriosis. One of the top bacteria to pop up was Fusobacterium, a group already known to be able to cause gum disease and skin ulcers.
Kondo, Muraoko and colleagues then went to their own collection of uterus and other tissues from women with and without endometriosis to see if they could find Fusobacterium too. The results were really striking – more than half the women with endometriosis had Fusobacterium in their uterine tissues compared to less than 10% of those without endometriosis.
Of course, this isn’t enough evidence to say Fusobacterium bacteria are actively involved in causing endometriosis, so the researchers dug a little deeper. In one set of lab experiments, they exposed endometrial cells to the bacteria to see what would happen to them. The cells began to grow and divide, move around, and stick in new places. Oh dear. Being able to do all those things would help the cells grow in places they aren’t supposed to.
Next the researchers moved to laboratory mice. If you are curious how mice can be used to study endometriosis, it turns out that if you inject endometrial tissue from one mouse into another mouse’s abdomen (all under anaesthesia and with plenty of medicine to prevent them feeling any pain), the recipient mouse will develop lesions made from that endometrial tissue. To see how Fusobacterium might be involved, the researchers also took endometrial tissue from donor mice that had been vaginally inoculated with the bacterium.
The result? Mice injected with the tissue from the Fusobacterium-exposed donor mice had about twice as many lesions as mice injected with tissue from control donor mice. And the lesions weighed more. To check if this result was specific to Fusobacterium, the researchers repeated their experiments with tissue from donor mice exposed to two other types of bacteria. This time there was no difference in the number or weight of the lesions that developed in the injected mice.
This is where I start getting really excited.
Because a five-day course of antibiotics was enough to reduce the number and weight of the lesions in those mice whose endometriosis was caused by the injection of tissue from Fusobacterium-exposed donor mice.
What we urgently need now are clinical trials in people as this could be a complete game-changer for treating endometriosis. Because if these results translated from mice to humans, one day all it might take to help some people with this debilitating condition could be a quick swab to see if they have Fusobacterium, and then a course of antibiotics. Fingers crossed!