The findings have been published in the scientific journal Nature Medicine.

Epidemiological studies have indicated links between high antibiotic use and an increased risk of certain health conditions, such as type 2 diabetes and gastrointestinal infections. The reasons for these observations are not fully understood, but changes in the gut microbiome are thought to play a role.

Strong links between antibiotic use and composition of gut microbiome

An international research team, led by scientists at Uppsala University, has now found strong links between a person’s history of antibiotic use and the composition of their gut microbiome, including the diversity of bacterial species.

“We can see that antibiotic use as far back as four to eight years ago is linked to the composition of a person’s gut microbiome today. Even a single course of treatment with certain types of antibiotics leaves traces,” says Gabriel Baldanzi, the first author of the study and a former doctoral student at Uppsala University.

The study was made possible by Sweden’s comprehensive prescribed drug register, which contains information on all antibiotics dispensed at pharmacies.

In the study, the researchers analysed drug register data alongside a detailed mapping of the gut microbiome of 14,979 adults living in Sweden. The gut microbiome was compared between participants who had received different types of antibiotics and those who had not received any at all during the period. The study was made possible by Sweden’s comprehensive prescribed drug register, which contains information on all antibiotics dispensed at pharmacies. The researchers were then able to link this data to Swedish biobanks at Uppsala and Lund University containing gut microbiome data.

Stronger association with certain types of antibiotics

The researchers found that the results differed substantially depending on the type of antibiotic used. The strongest associations were observed for clindamycin, fluoroquinolones and flucloxacillin. By contrast, penicillin V, the most commonly prescribed antibiotic for the treatment of infections outside hospitals in Sweden, was linked to small and short-lasting microbiome changes.

Penicillin V, the most commonly prescribed antibiotic for the treatment of infections outside hospitals in Sweden, was linked to small and short-lasting microbiome changes.

“The strong link between the narrow-spectrum flucloxacillin and the gut microbiome was unexpected, and we would like to see this finding confirmed in other studies. However, we believe that the findings of our study may 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,” says Tove Fall, Professor of Molecular Epidemiology at Uppsala University and principal investigator of the study.

A longer follow-up period could provide further insights

The researchers acknowledge that the study only covered prescriptions from the previous eight years and that a longer follow-up period could provide further insights. Another aspect is that the gut microbiome was sampled only once per participant.

“We are currently collecting a second sample from almost half of the participants,” says Fall. “This will enable us to gain an even better understanding of the recovery time and identify which gut microbiomes are more susceptible to disruption following antibiotic treatment.”