Researchers have found that the microbiota of each individual determines the maintenance of antibiotic-resistant bacteria in the gut: whereas in some individuals resistant bacteria are quickly eliminated, in others they are not. The study, published in Nature Ecology and Evolution, reinforces the need to implement more personalized therapies and offers new insights to the paradigm of the evolution of antibiotic resistance in the gut.

Antibiotic resistance is a growing challenge in the treatment of infectious diseases worldwide. Bacteria become resistant to antibiotic through mutations or by acquiring genes that allow them to survive to the administration of drugs, which otherwise would be able to kill them. However, this advantage could have repercussions for the bacteria when the drug stops being administered. Becoming resistant affects genes that assure essential functions of the bacterial cell and once back to the initial context, without antibiotics, the bacteria is no longer able to compete for its survival.

Till now, much of what is known about this process relies on studies in artificial systems, that give an incomplete overview of the phenomenon’s complexity. In order to fill this gap, researchers led by Isabel Gordo, principal investigator at IGC, used mice as a model and observed that in the gut after the antibiotic intake, the competition for survival of resistant bacteria has different dynamics overtime, depending on the host. The same resistance has different interactions which determine which lead to resistant bacteria with low survival capacity in the absence of antibiotics in one individual and to bacteria with high survival capacity in another individual.

Using Escherichia coli, researchers found out that the resistance of a bacteria is due to variations in the gut flora (or microbiota) of each host. “We noted that in mice without microbiota there are no differences in the survival dynamics of resistant bacteria, that always suffer damage and can not survive” explains Isabel Gordo. In contrast, mice with very diverse gut flora showed a “high variability in the survival dynamic of the resistant bacteria, specific of each host, drawing a causal link between individual microbiota and the survival of antibiotic-resistant bacteria”, states Isabel.

The next steps of this research will be aimed at “finding the Achilles heel of resistant bacteria in the gut, a study we are carrying out in several levels” says Isabel Gordo, “at least one of the hypothesis is showing great results: even when they colonize the gut in a less ideal condition we are being able to eliminate them faster!”.