A pharmaceutical or cosmetic composition is provided. The composition includes an Indigo Naturalis or Indigo-producing plant extract, for inhibiting Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus. A method of inhibiting Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus, is also provided. The method includes contacting a cell with an effective amount of an Indigo Naturalis or Indigo-producing plant extract.