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Understanding Methicillin-Resistant Staphylococcus aureus

Author(s): by Mary Pat Bolton, MA, RD, LD

What is Methicillin-Resistant Staphylococcus aureus?

Staphylococcus is a genus of gram positive bacteria (approximately 0.5–1.0 µm in diameter), of more than 30 species. Members of this genus are sphere-shaped and grow in clusters, pairs, and occasionally short chains. MRSA (Methicillin-Resistant Staphylococcus aureus) is a strain of Staphylococcus aureus bacteria that has developed resistance to an entire class of antibiotics (called beta lactams), including methicillin, penicillin, amoxicillin, and oxacillin. In addition, S. aureus is often found to be resistant to antiseptics and disinfectants. Over the past four decades in the US, it has evolved from an easily controlled microbe to a major public health problem.