Antibiotic treatment disrupts the balance of beneficial and harmful bacteria in a person’s gut. That disruption can lead to the overgrowth of fungal species in the gut mycobiota, including the common intestinal yeast Candida albicans. However, researchers only have a limited understanding of the underlying mechanisms. Researchers now report on how treatment with a common beta-lactam antibiotic led to significant changes in C. albicans in patients.