Gut bacteria would appear to be on a roll.
They account for about 95% of the microbiome, that cocktail of microbes which call your body home, and whose composition influences risk for conditions as diverse as depression, diabetes, allergy and obesity.
A new study adds to our esteem for this colony of bacteria, showing it may protect us from inflammatory bowel disease (IBD), an effect that could be seriously undermined in the children of pregnant women who take antibiotics.
The research, led by microbiologist Martin Blaser from New York University’s Langone Medical Centre, US, took its lead from several troubling facts.
A disturbingly high number of women take antibiotics in pregnancy. A UK study found a third of pregnant women were prescribed antibiotics by a family doctor, mostly for respiratory, urinary tract, skin and ear infections.
Antibiotics also change the balance of gut bacteria. And their use in children increases the risk of IBD, an illness that delivers crippling abdominal pain, bloody stools and, for good measure, a heightened risk of cancer of the colon and rectum.
As it happens, a baby’s microbiome is massively influenced by the population of bacteria that inhabit the mother. During a vaginal birth the infant picks up mum’s bugs from the genital tract and from poo that tends to appear at the same time.
The researchers wondered, therefore, if maternal antibiotic use could be linked to IBD risk in their progeny.
To find out they wrested control of the gut microbiota of pregnant mice, passing a tube into their stomachs and squirting in the intestinal contents of other mice, whose gut flora had been modified by treatment with antibiotics. The procedure successfully reduced the diversity of gut microbes in the pregnant mice, on a par with their antibiotic-treated donors.
The researchers then discovered the gut microbes of offspring mirrored the new, antibiotic-induced bacteria profile of the mother.
To assess whether that change affected the offspring’s risk of IBD, the authors deployed a class of mouse deficient in an immune protein called interleukin 10 (IL-10), something known to raise the risk of IBD.
The results were emphatic.
IL-10 deficient pups with the altered microbiome had a 55-fold increase in IBD – causing severe weight loss, bloody stools and prolapse of the rectum – compared to IL-10 deficient pups with gut flora undisturbed by antibiotics.
The investigators’ decision to use antibiotic-treated innocula, rather than giving the pregnant mice antibiotics directly, neatly showed that altered gut bacteria, rather than any specific effect of the antibiotics, were causing the IBD symptoms.
Commenting on their findings, Professor Blaser says: “Our results provide strong evidence that antibiotics change the baby’s inherited microbial communities with long-term disease consequences, which is especially important given the widespread use of antibiotics in young women before and during pregnancy.”
The study appeared in the journal Nature Microbiology.
Paul Biegler is a philosopher, physician and Adjunct Research Fellow in Bioethics at Monash University. He received the 2012 Australasian Association of Philosophy Media Prize and his book The Ethical Treatment of Depression (MIT Press 2011) won the Australian Museum Eureka Prize for Research in Ethics.
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