Giving antibiotics to young mice is likely to make them more aggressive in later life, according to a new study.

Researchers at Bar-Ilan University in Ramat Gan, central Israel, believe their findings could well apply to humans as well.

They say there is a significant link between antibiotics – medication used to treat bacterial infections – and the diverse microorganisms of the gut, known as the microbiome.

Antibiotics given in infancy can disrupt the development and limit the diversity of the microbiome, they say, resulting in increased levels of aggression.

The study used “humanized” mice that had been implanted with intestinal bacteria from infants who had received antibiotics shortly after birth.

“This approach enhances the relevance of the findings to human health and behavior, providing insights into how early-life antibiotic exposure can shape future social behaviors,” they explained in a news release.

The researchers measured aggression levels by introducing a foreign mouse into the home cage of a resident mouse and observing its reactions.

“Our findings are revolutionary,” said Prof. Omry Koren, who led the study at BIU’s Azrieli Faculty of Medicine with graduate student Atara Uzan-Yuzari. “They suggest that a disrupted microbiome during critical developmental periods can lead to persistent aggressive behaviors later in life.”

This opens up new avenues for understanding how early-life interventions could influence long-term behavioral outcomes and for developing strategies to mitigate these effects.

The study, published in the journal Brain, Behavior, and Immunity, builds on previous experiments carried out on fruit flies. Using mice, especially those implanted with the human microbiome, takes the investigation a step further, examining behavioral, biochemical and neurological changes.

“This study sheds light on the role of the gut microbiome in modulating aggression and highlights its potential avenues of action, offering insights for development of therapeutic strategies for aggression-related disorders,” say the authors.

The study was funded by a European Research Council grant.