The direct toxic effects of antibiotics on the intestine can alter digestive functions and cause pathogenic bacterial overgrowth leading to antibiotic-associated diarrhea (AAD). Clostridium difficile ( C. difficile ) is widely known to be responsible for 10~20% of AAD cases. However, Kle b siella o x y t o c a , Clo s t ridiu m p e rfrin g e n s , Staphylococcus aureus , and Candida species might also contribute to AAD.