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Staphylococcus aureus

Staphylococcus areus

Staphylococcus aureus is a bacterium that commonly colonises human skin and mucosa (e.g. inside the nose) without causing any problems. It can also cause disease, particularly if there is an opportunity for the bacteria to enter the body, for example through broken skin or a medical procedure.

Image courtesy of K Hiramatsu

If the bacteria enter the body, illnesses which range from mild to life-threatening may then develop. These include skin and wound infections, infected eczema, abscesses or joint infections, infections of the heart valves (endocarditis), pneumonia and bacteraemia (blood stream infection). Staphylococcus aureus also produces toxins, which if the bacteria contaminate incorrectly prepared food can cause food poisoning and have also been linked with toxic shock syndrome. Some strains also produce another toxin called PVL, these tend to cause more severe disease.
Most strains of S. aureus are sensitive to the more commonly used antibiotics, and infections can be effectively treated. Some S. aureus bacteria are more resistant. Those resistant to the antibiotic meticillin are termed meticillin-resistant Staphylococcus aureus (MRSA) and often require different types of antibiotic to treat them. Those that are sensitive to meticillin are termed meticillin-sensitive Staphylococcus aureus (MSSA). MRSA and MSSA only differ in their degree of antibiotic resistance: other than that there is no real difference between them.