Antibiotics Leave Lasting Gut Footprint Years Later, Study Finds

A large-scale human data study has revealed that a single course of antibiotics may leave a measurable microbial footprint in the gut microbiome years later, raising questions about long-term health effects and prescribing practices.

The study, published in Nature Medicine, linked Swedish prescription registry data with fecal metagenomic profiles from nearly 15,000 adults.

Even a single antibiotic course taken four to eight years prior was associated with lasting differences in microbiome composition.

How the Study Was Conducted

Researchers examined the influence of oral antibiotic use over the previous eight years on gut microbial composition. They linked prescription data from the Swedish National Prescribed Drug Register with fecal metagenomic data from three cohorts: SCAPIS, SIMPLER, and MOS. Antibiotic exposure was assessed across three time windows: within 1 year, 1 to 4 years, and 4 to 8 years before sampling.

Persistent Microbial Shifts Identified

Microbial diversity reductions were largest within one year of antibiotic use. However, significant associations persisted for exposures one to four years earlier, and even four to eight years earlier. Each additional course was linked to further declines in diversity. A single course taken years earlier was associated with long-term differences in the microbiome.

Specific Antibiotics and Species Impact

Clindamycin, fluoroquinolones, and flucloxacillin demonstrated the strongest and most persistent effects, altering the relative abundance of approximately 10-15% of microbial species. Beneficial species like Alistipes communis and Odoribacter splanchnicus declined. Meanwhile, species associated with metabolic risk, including Ruminococcus gnavus, Flavonifractor plautii, and Eggerthella lenta, increased. Penicillin V showed minimal effects.

Incomplete Recovery and Implications

Microbiome recovery was fastest within the first two years after antibiotic use but slowed thereafter and was often incomplete. Recovery varied by antibiotic class, sex, and age. These findings suggest that some antibiotics may have long-lasting effects on the gut microbiome, supporting more judicious antibiotic prescribing and stewardship strategies.

Study Caveats

The study is observational and does not establish causality. Further research is needed to understand long-term health consequences and links to chronic disease. The findings may not generalize beyond outpatient settings in Sweden and could underestimate total antibiotic exposure.