Taking antibiotics can affect the composition of the gut bacterial community—the gut microbiome—for a long time, but according to a new study, the impact of some of these drugs can last up to eight years. The research, led by scientists from Uppsala University (Sweden) and published this Wednesday in Nature Medicine, is based on the analysis of the microbiome of 15,000 people; some had taken antibiotics and others had not in the last eight years. Although antibiotics protect against serious infections, their misuse increases the risk of certain conditions, such as type 2 diabetes and gastrointestinal infections. Scientists believe that the changes in the microbiome caused by these drugs could be behind these pathologies. But while it is known that antibiotics have a significant short-term impact on the microbiome, their long-term effects have been little studied. To find out, the team analyzed the gut microbiome of 14,979 residents in Sweden and compared the microbiome of participants who had taken different types of antibiotics in the last eight years with those who had not. The analyses revealed strong links between antibiotic use and the composition of each person's gut microbiome, including the diversity of bacterial species. "We can see that the use of antibiotics from four to eight years ago is linked to a person's gut microbiome composition today. Even a single course of treatment with certain types of antibiotics leaves traces," states Gabriel Baldanzi, the study's first author and a former PhD student at Uppsala University. The study was made possible by Sweden's comprehensive registry of prescription medications, which contains information on all antibiotics dispensed at pharmacies: "Antibiotic use is taken very seriously in Sweden, and the country already has strict management of them," the statement says. Not all antibiotics are the same The study found that the results differed substantially depending on the type of antibiotic used. The strongest associations were observed with clindamycin, fluoroquinolones, and flucloxacillin, while penicillin V—the most prescribed antibiotic for treating infections outside of hospitals in Sweden—was associated with small and short-term changes in the microbiome. "The strong link between narrow-spectrum flucloxacillin and the gut microbiome was unexpected, and we would like to see this finding confirmed in other studies," comments Tove Fall, Professor of Molecular Epidemiology at Uppsala University and principal investigator of the study. Fall believes that the study's findings can help inform future recommendations on antibiotic use, "especially when choosing between two equally effective antibiotics, one of which has a weaker impact on the gut microbiome." Since the study only considered prescriptions from the last eight years, scientists believe that conducting a study with a longer follow-up period could provide more information. Additionally, the gut microbiome was sampled only once per participant, so the team is currently collecting a second sample from nearly half of the participants. "This will allow us to gain an even better understanding of the recovery time and to identify which gut microbiomes are most susceptible to disruption after antibiotic treatment," Fall concludes.
