Methycillin Resistant Staphylococcus Aureus or MRSA

Although S. aureus has been causing infections (staph infections) probably as long as the human race has existed, MRSA has a relatively short history.

MRSA was first noted in 1961, about two years after the antibiotic methicillin was initially used to treat S. aureus and other infectious bacteria. The resistance to methicillin was due to a penicillin-binding protein coded for by a mobile genetic element termed the methicillin resistant gene (mecA).

In recent years, the gene has continued to evolve so that many MRSA strains are currently resistant to several different antibiotics. S. aureus is sometimes termed a "superbug" because of its ability to become resistant to several antibiotics. Unfortunately, MRSA can be found worldwide.

MRSA belongs to the large group of bacteria known as Staphylococci, often referred to as Staph. About 25%-30% of all people have Staph within the nose, but it normally does not cause an infection. In contrast, only about 1% of the population have MRSA.

Infections with MRSA are most common in hospitals and other institutional health-care settings, such as nursing homes, where they tend to strike older people, those who are very ill, and people with a weakened immune system. In health-care settings, MRSA is a frequent cause of surgical wound infections, urinary tract infections, bloodstream infections (sepsis), and pneumonia.

MRSA outbreaks, however, are appearing increasingly in the community. Infections can occur in people who have not been hospitalized or had a medical procedure performed in the past year, and who do not have immune deficiency. These infections are termed community-associated MRSA infections (CA-MRSA).