Microsoft word - mrsa_is1a.doc

What is MRSA?
Information sheet A – What is MRSA?
Staphylococcus aureus is a common bacterium that lives harmlessly on the skin and in the nose of about one third of the population. It was first identified in the 1880s when doctors realised it was the most common cause of infected surgical wounds. When penicillin was introduced in the 1940s, it helped tackle these infections but, by 1959, about 90–95% of Staphylococcus aureus strains isolated from infected patients were found to be resistant to the antibiotic. Methicillin was developed from penicillin, to treat these new strains. MRSA is short for methicillin-resistant Staphylococcus aureus – a type of Staphylococcus aureus that is resistant to the antibacterial activity of methicillin. Although the first case of MRSA was reported in England within a year of the launch of methicillin, MRSA was relatively uncommon through the 1960s and 1970s. However, by the mid-1990s, ‘epidemic’ strains of MRSA had become established in hospitals throughout the UK. These strains of MRSA are easily transmissible and are sometimes called ‘superbugs’ because they are resistant to some antibiotics. There is no specific ‘MRSA disease’, as there is with tuberculosis or typhoid, for example. Infections occur when MRSA gets into the body, and can cause a broad spectrum of symptoms depending on the part of the body that is infected. Infection can cause conditions ranging from potentially fatal septicaemia to asymptomatic colonisation, where the patient is carrying MRSA bacteria but has no symptoms. Carriers can be a source of infection for themselves (for example, they could infect themselves if they have a wound), and they can also infect others when the bacteria are passed on – on people’s hands, or on infected equipment, or through the environment. MRSA exists because of evolution. There are many different strains of any single type of bacteria, and each strain has small natural genetic variations that make it different from the others. In addition, bacterial genes are constantly mutating. So some bacteria become naturally resistant to some antibiotics, simply because of chance mutations in their genes. When most bacteria encounter antibiotics, they die, but those carrying resistance genes may survive and multiply. Antibiotics are not completely powerless against MRSA, but patients require a much higher dose over a longer period, or the use of an alternative antibiotic to which MRSA has less resistance. Doctors are now careful to only prescribe antibiotics when essential, and patients should always finish the entire course. Otherwise not all the bacteria, will be killed and the ones that survive are likely to be those that are resistant to antibiotics. To reduce the spread of MRSA in hospitals, visitors and staff should wash their hands using soap or antibacterial alcohol solutions before and after having physical contact with patients. Other measures include regular cleaning of wards, and keeping patients who are colonised or infected with MRSA away from other patients. Association for Science Education 2008. ASE is grateful for support from the Department for Education and Skills in developing this project. Teachers and others who download this material may use it freely within their institution. For any other usage consult the ASE, satis@ase.org.uk ASE is not responsible for any revision that may be made to the material after it has been downloaded.

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