The study, which was published in Mucosal Immunology, has offered the clearest proof to date that the long-recognized link between early antibiotic exposure and the later onset of asthma and allergies is causal.
In the study, the researchers found that the gut microbiome ecosystems and metabolic processes are impacted by antibiotics, one of the most commonly prescribed drugs for children.
Host immunity may be impacted by these changes in microbiota structure.
Mice that were five days old were given water, azithromycin, or amoxicillin in the initial phase of the trial. After the mice reached adulthood, scientists exposed them to a typical allergen made by house dust mites. Mice that had received either antibiotic, particularly azithromycin, displayed increased immunological reactions, or allergies.
“The practical implication is simple: Avoid antibiotic use in young children whenever you can because it may elevate the risk of significant, long-term problems with allergy and/or asthma,” said senior author Martin Blaser, director of the Center for Advanced Biotechnology and Medicine at Rutgers.
The experiment’s second and third phases evaluated the idea that early antibiotic exposure results in allergies and asthma by eradicating some beneficial gut bacteria that aid in optimal immune system development.
Timothy Borbet, the lead author, initially transferred fecal samples rich in bacteria from the first group of mice to a second group of adult mice that had never been exposed to any bacteria or germs. Some people obtained samples from mice given amoxicillin or azithromycin as babies.
From mice that had been given water, other people received typical samples. Similar to how adults who use antibiotics are not more likely to develop allergies or asthma than those who do not, mice who received samples tainted with antibiotics were not more susceptible than other mice to generate immunological responses to house dust mites.
For the following generation, however, things were different. Mice that received antibiotics as newborns reacted more to the allergen than mice that received water, and offspring of mice who got antibiotic-altered specimens responded more to house dust mites than those whose parents got samples unaffected by antibiotics.
“This was a carefully controlled experiment,” said Blaser. “The only variable in the first part was antibiotic exposure. The only variable in the second two parts was whether the mixture of gut bacteria had been affected by antibiotics. Everything else about the mice was identical.
These studies give compelling evidence that antibiotics cause the development of undesirable immune responses through their impact on gut bacteria, but only if gut bacteria are altered in early life, Blaser continued.
Parvathy Sukumaran 
