Antibiotics alter the bacterial community in the mouse gut in ways that might make the animal more susceptible to infections from the dangerous, diarrhoea-causing bacterium Clostridium difficile.

Vincent Young and his team at the University of Michigan in Ann Arbor analysed the molecules produced by gut microbes and found that antibiotics shifted the levels of carbohydrates and other metabolites.

Compounds that became more abundant with antibiotic treatment such as the sugar alcohols mannitol and sorbitol boosted the growth of C. difficile cells in culture. A bile acid that also increased in treated mice triggered spores of the bacterium to germinate. Moreover, the intestinal contents from mice given antibiotics promoted the growth of C. difficile, whereas those from untreated mice did not.

The results could explain why people taking antibiotics have a high risk of C. difficile infection.

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