Gram positive bacteria appear purple when stained using the Gram stain. Common Gram positive bacteria include staphylococci, streptococci, enterococci and clostridia. Staphylococci, streptococci and enterococci are Gram positive cocci, implying that their shape is round, like a ball. Examples of Gram positive cocci include Staphylococcus aureus (including MRSA), Streptococcus pneumoniae and Enterococcus (including VRE). Clostridium difficile is also Gram positive although its shape is rod-like, and is referred to as a Gram positive bacillus. With some exceptions, such as VRE, vancomycin is highly active against Gram positive bacteria.