Antibiotics that reduce gut bacteria linked to obesity By Steve Connor

Scientists believe that the widespread use of antibiotics may be playing a significant role in exacerbating the obesity epidemic.

Growing evidence suggests that oral antibiotic medicines may be affecting the growth of beneficial bacteria in the human intestine which is influencing whether some people put on weight when they overeat or take too little exercise, they said.

The latest study, which has yet to be published in a peer-reviewed scientific journal, centres on a technique for counting the bacterial genes in the human intestine. It found that lean people are likely to have a more diverse community of gut flora compared to obese individuals.

Previous work has already established a difference in the gut bacteria of lean and overweight people, but the latest work is being seen as lending support to the controversial idea that bacteria-killing antibiotics may be playing a role in predisposing some people to being fat.

"It is a very real possibility," said Stanislav Dusko Ehrlich, a microbiologist at the French National Institute for Agricultural Research in Jouy-en-Josas, who was part of the Meta-HIT consortium of pan-European scientists who carried out the work.

"What we have found is that bacterial communities in the gut appear to be different between lean and obese people. We can't be certain whether that perturbation is the cause, contribution or consequence of being overweight. But these bacteria are candidates for being a cause and that must be investigated," he said.

Previous studies on laboratory mice and farm animals have established a link between gut flora, the use of antibiotics and an increase in body fat, but scientists have been wary of extrapolating these findings to humans.

The study investigated the bacterial genes found in the gut flora of 177 Danish people, 55 of whom were lean, with the rest either overweight or obese. Scientists in the Meta-HIT consortium found that most people in the study carried in their intestines around 600,000 distinct bacterial genes. But about a third of the obese participants had only about 360,000 bacterial genes – about 30 or 40 per cent fewer – which suggests they possessed a distinctly poorer community of gut flora, which is typically composed of about 160 different species of microbial lifeforms.

Microbes that live inside us

* The healthy human gut contains 100 trillion microbial cells, 10 times as many as the human cells that comprise the body.

* About 1,000 species of microbe can live in the human gut, but at any one time a person typically has about 160.

* Members of the same family tend to have similar communities of gut bacteria.

* The two dominant groups of gutbacteria, the Bacteroidetes and the Firmicutes, help us to break down food.