Which antibiotics are most strongly associated with C. difficile infection?

• A. Narrow-spectrum antibiotics
• B. Aminoglycosides
• C. Macrolides
• D. Broad-spectrum antibiotics

Answer: (D)

Disruption of the normal gut microbiota is what allows C. difficile to overgrow and produce toxins that cause infection. Broad-spectrum antibiotics wipe out a wide range of bacteria in the colon, including many anaerobes that normally keep C. difficile in check. With these competing microbes suppressed, C. difficile spores can germinate, toxins are produced, and inflammation and colitis follow.

Narrow-spectrum antibiotics affect a specific group of organisms and usually spare much of the gut flora, so they disturb the colon's microbial balance less. Aminoglycosides act mainly in the gut only if given orally and are poorly absorbed, so they have a smaller impact on the colonic microbiome. Macrolides also have a relatively narrower effect on gut bacteria compared to broad-spectrum agents. Because they disrupt the microbiome to a lesser extent, they are less strongly associated with C. difficile infection than broad-spectrum antibiotics.