Final answer:
Clostridium difficile is the bacterium responsible for causing life-threatening pseudomembranous colitis, often following antibiotic use that disrupts normal gut microbiota. The answer is option A.
Step-by-step explanation:
The bacterium that can cause life-threatening pseudomembranous colitis is Clostridium difficile (C. difficile). This is a gram-positive, rod-shaped bacterium that becomes problematic primarily after the normal gut microbiota is eradicated by antibiotic use. Infections with C. difficile lead to severe inflammation of the colon and development of a pseudomembrane.
produced by C. difficile, such as toxin A (TcdA) and toxin B (TcdB), are responsible for damage to the intestinal lining and can trigger severe diarrheal illness, which, if unchecked, can lead to perforation of the colon, septicemia, shock, and death. C. difficile is a significant concern in healthcare settings, especially among patients who are immunocompromised, elderly, have recently taken antibiotics, or have been in health-care environments for extended periods.