"Methicillin resistant Staphylococcus aureus
MRSA is the term used for bacteria of the Staphylococcus aureus group (S. aureus) that are resistant to the usual antibiotics used in the treatment of infections with such organisms. Traditionally MRSA stood for methicillin resistance but the term increasingly refers to a multi-drug resistant group. Such bacteria often have resistance to many antibiotics traditionally used against S.aureus.
This resistance to methicillin is due to the presence of the mec gene in the bacteria. This alters the site at which methicillin binds to kill the organism. Hence, methicillin is not able to effectively bind to the bacteria.
Infections caused by MRSA are the same as other staphylococcal infections because the organism itself is not any more virulent (or infectious) than usual type S.aureus.
Like other S.aureus, MRSA can colonise the skin and body of an individual without causing sickness, and in this way it can be passed on to other individuals unknowingly. Problems arise in the treatment of overt infections with MRSA because antibiotic choice is very limited. "