Final answer:
Mucous membranes are key barriers to pathogen entry, lining several body areas and producing mucus to trap pathogens. Some pathogens, like Clostridium difficile, can overcome these barriers and cause infection, especially after antibiotic use.
Step-by-step explanation:
Mucous membranes act as a mechanical barrier to pathogens at various body openings. These membranes, which line the respiratory, gastrointestinal, urinary, and reproductive tracts, produce mucus that traps pathogens. In addition, cilia on these membranes sweep mucus and pathogens out of the body.
However, some pathogens have developed mechanisms to breach these barriers. For example, Clostridium difficile can colonize the mucous membrane of the colon after the normal microbiota is disrupted, often due to antibiotic treatment. C. difficile releases toxins that cause inflammation and may lead to the formation of a pseudomembrane, signifying an infection.