Everyone knows that antibiotics kill useful bacteria found in human gut. Some doctors prescribe probiotics to go with antibiotics to reduce potential adverse side effects. However, most people think that these negative effects are temporary. Now scientists from UCL found that the composition of oral and gut microbiomes is changed for at least a year after a course of antibiotics.

There are like 10-100 trillion microorganisms such as bacteria, viruses, fungi and microscopic animals that live all over our bodies. Most of the bacteria live in our gut. It is quite interesting that we don’t quite understand how much it affects our health. But we do know maintaining healthy microbiomes is beneficial. People already know that antibiotics are able to alter the composition and the balance of the community of gut bacteria. But only now, after tracking the diversity of microbes over a longer period of time, scientists begin to understand that these changes are not as short as we would think. In fact, microbiomes couldbe changed permanently after a single course of antibiotics.

Scientists analysed data about four common antibiotics (ciprofloxacin, clindamycin, minocyline and amoxicillin) and compared it with a placebo. Ciprofloxacin and clindamycin seemed to be causing the biggest disturbance in the gut microbiome, but all antibiotics have a long-lasting negative effect. Interestingly, antibiotics increased diversity of the oral bacteria, but reduced it in gut bacteria. Effects of clindamycin were still visible after one year, but it is likely that communities of gut bacteria never return to their original constitution. These negative side effects are observable even after one course of antibiotics – it is likely that the more antibiotics you take, the worse it gets.

These issues are important to everyone, but especially for children in the developing world. They are more prone to infections and antibiotics are overused more than in the developed countries. Dr Liam Shaw, first author of the study, said: “We do know that where gut populations of microbes take a long time to recover, or sometimes don’t recover at all, individuals are likely to be at more risk from colonisation and overgrowth of pathogenic species”.

Despite all the negative press that they are getting nowadays, antibiotics are still extremely necessary to us. In many cases they represent the most effective treatment opportunity. However, the problem is that people overuse antibiotics in cases when other treatment options should be preferred. Hopefully researches like this one will help changing these practices and making more informed decisions.