抗生素與腸道

Dysbiosis
Does taking antibiotics change the composition of the microbiota? And if it does, how long does the effect last? Most people will have experienced the bloating and diarrhea that often seem to accompany a course of antibiotics. It is the most common side effect of antibiotic treatment, and of course it is the result of disruption to the microbiota --- dysbiosis. Usually, it clears up within a few days of finishing treatment. But what of the microbes left behind? Do they regain a normal healthy balance?

Evidence
A team of researchers in Sweden asked this very question in 2007. They were particularly interested in what happens to Bacteroides species, as these bacteria specialize in digesting carbohydrates from plants and they have a big impact on human metabolism. The researchers split a group of healthy volunteers into two, and gave half of them the antibiotic clindamycin for seven days, and the other half no treatment at all. The gut microbes of those given clindamycin were dramatically affected immediately after receiving the drugs. The Bacteroides, in particularly, sharply declined in their diversity. The microbiota of both groups were assessed every few months, but by the end of the stdu the Bacteroides of the clindamycin group had sill not returned to their original composition. Their treatment had finished two years previously.

Overweight
Epidemiological studies had shown that human babies given antibiotics in the first six months were more likely to become overweight than those who made it past their first birthday without being exposed to the drugs. The same went for farm animals --- to get the best weight-boosting effect, it's important to start providing antibiotics as early as possible.

AOBs
David Whitlock was a chemical engineer who studied the microbes found in the soil. While collecting the soil samples from a stable yard in 2001, he was asked why horses loved to roll in the dirt. He didn't know, but the question got him thinking. Whitlock knew that soil and natural water sources contained a lot of ammonia-oxidizing bacteria (AOBs). He also knew that sweat contained ammonia, and he wondered if horses and other animals used the AOBs in the soil to manage the ammonia build-up on their skin.

Collen, A. (2015) 10% Human: How Your Body's Microbes Hold the Key to Health and Happiness. London: William Collins.