Methicillin-resistant Staphylococcus aureus (MRSA) infection is one type of infection caused by the Staphylococcus aureus bacteria, or simply staph, whose one strain is known to resist almost all available antibiotics ever developed.Depending on an infected person's immune system, effects of staph can range from simple skin infections to MRSA. Sometimes, howeever, it may not cause anything.
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MRSA infection - MayoClinic.com