C. difficile (or C. diff) is a Gram-positive, spore-forming, anaerobic bacterium that represents the leading cause of nosocomial (hospital-acquired) antibiotic-associated diarrhea and pseudomembranous colitis. TcdA (Clostridium difficile toxin A) is a toxin generated by Clostridium difficile. It is similar to Clostridium difficile Toxin B. The toxins are the main virulence factors produced by the gram positive, anaerobic, Clostridium difficile bacteria. The toxins function by damaging the intestinal mucosa and cause the symptoms of C. difficile infection, including pseudomembranous colitis.