Staphylococcus aureus is a bacteria that lives in the upper respiratory tract as well as living on the skin. It is a bacteria that causes an infection in the host. There are about four types of staph bacteria, but we will be talking about Methicillin-Resistant Staphylococcus Aureus also known as MRSA. About 30% of people carry MRSA and do not know whatthat they do because it is so harmless when it is just lying on the skin or in the upper respiratory tract dormant. This is known as colonized MRSA, which means that a person has MRSA on the skin or in the nose but is not infected with it, and therefore can not infect other people. The only time it is an issue is when it finds its way through broken skin and then that. That is when it starts to do theits real damage.