Which antimicrobial peptide is secreted by resident microbiota in the gastrointestinal tract and inhibits bacteria by disrupting membranes?

• A. Bacteriocins
• B. Cathelicidin
• C. Defensins
• D. Dermcidin

Answer: (A)

Bacteriocins are antimicrobial peptides produced by bacteria, including those living in the gastrointestinal tract. They are secreted by resident gut microbes and kill neighboring bacteria by disrupting their membranes, often by forming pores or otherwise compromising the lipid bilayer. This membrane disruption leads to ion leakage, loss of membrane potential, and cell death, which is exactly how these peptides curb competing bacteria in the gut environment. While host-derived peptides like cathelicidins and defensins also disrupt membranes, they are produced by human cells, not by the resident microbiota. Dermcidin comes from sweat glands, not the GI tract. So the described scenario best fits bacteriocins, the microbial peptides that target competitors through membrane disruption. An example you might recall is nisin, a bacteriocin from Lactococcus lactis that disrupts membranes in susceptible bacteria.