ANTIBIOTICS can cause long-lasting changes in the bacteria living in the human gut. As changes in gut flora could increase the risk of some chronic diseases, such as inflammatory bowel syndrome, each course of antibiotics may represent a trade-off between short-term benefit and long-term risk.
Les Dethlefsen and David Relman of Stanford University in California collected more than 50 stool samples from three people over a 10-month period that included two courses of the antibiotic ciprofloxacin. They used gene sequencing to identify the microbial strains present in each sample. They found that each person had a unique set of microbial flora, the composition of which fluctuated around an equilibrium which was disrupted by each course of drugs.
In most cases, the composition quickly returned to its previous state, but in a few, bacterial species present before treatment were replaced by related species. One person completely lost a common genus of bacteria, which did not return for the duration of the study (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1000087107).
Each round of antibiotics is a roll of the dice that could lead to lasting changes in a person’s gut microbes, says Dethlefsen. The work shows that antibiotics should be used only when truly necessary, he says.