If an individual's gut microbiome is significantly altered due to antibiotic treatment, which of the following is the most likely underlying cause of this effect on their health?

Antibiotics can kill many of the bacteria that normally live in the gut, leaving fewer species to compete for resources. This loss of microbial diversity means that the remaining bacteria can overgrow or allow harmful microbes to thrive, which can upset digestion and the immune system. Because the gut bacteria help train immune cells and break down food, their sudden decline can cause inflammation, diarrhea, or even infections elsewhere. For example, a person who takes broad‑spectrum antibiotics may develop a yeast overgrowth that leads to stomach discomfort and weakened immunity. Thus, the most likely underlying cause is the disruption of normal gut microbial balance, or dysbiosis, caused by the antibiotics.