MRSA

Abbreviation for methicillin-resistant Staphylococcus aureus, a bacterial strain that causes serious problems in hospitals.

While ordinary Staphylococcus aureus are widespread and can cause illnesses from wound infections through to toxic shock syndrome, they generally respond to standard antibiotics such as penicillin. MRSA, by contrast, which was first discovered in the UK in 1961, has acquired a gene known as mecA, making it resistant towards methicillin and a range of other antibiotics from the penicillin family.

MRSA spread dramatically in the 1990s. In the UK, the proportion of S. aureus samples tested positive for methicillin resistance rose from 2% in 1990 to a peak of 43% in 2002. Concerns over this development led to the reconsideration of hospital hygiene routines and the responsible use of antibiotics.

It has been estimated that more than 50 million people carry MRSA (2007), most of them without suffering any symptoms. In hospitals, patients with a compromised immune system, open wounds, or catheters, are particularly at risk of developing a symptomatic MRSA infection. While there are no definitive figures on mortality or morbidity, it is generally thought that MRSA infection represents a significant additional risk to vulnerable patients. MRSA normally responds to two antibiotics (vancomycin and teicoplanin) which are considered too toxic for use in any but life-threatening infections, but it still causes fatalities.

Complete genome sequences of MRSA and of a methicillin-sensitive strain were reported in 2004.