What is a potential consequence of disrupting the normal microbiota with broad-spectrum antibiotics?

• A. Disrupt microbiota, allowing opportunistic pathogens to overgrow
• B. Improve immune response
• C. Have no effect
• D. Kill human cells directly

Answer: (C)

Disrupting the normal microbiota with broad-spectrum antibiotics reduces colonization resistance in the gut. Commensal bacteria normally compete with pathogens for nutrients and space and help keep opportunistic organisms in check; when their populations drop, these opportunists can overgrow. A classic consequence is antibiotic-associated diarrhea from overgrowth of Clostridioides difficile, which can lead to colitis. Yeast overgrowth, such as Candida infections, can also occur as the balance of microbes shifts. Broad-spectrum antibiotics don’t kill human cells directly, nor do they inherently boost immune responses; the primary issue is the disturbance of microbial populations and the downstream risk of secondary infections.