English: This colorized 2005 scanning electron micrograph (SEM) depicted numerous clumps of methicillin-resistant Staphylococcus aureus bacteria, commonly referred to by the acronym, MRSA; Magnified 2390x.

Recently recognized outbreaks, or clusters of MRSA in community settings have been associated with strains that have some unique microbiologic and genetic properties, compared with the traditional hospital-based MRSA strains, which suggests some biologic properties, e.g., virulence factors like toxins, may allow the community strains to spread more easily, or cause more skin disease. A common strain named USA300-0114 has caused many such outbreaks in the United States. Please see PHIL 7822 for a black and white version of this image.

MRSA is a type of bacteria that is resistant to certain antibiotics. These antibiotics include methicillin and other more common antibiotics such as oxacillin, penicillin and amoxicillin. Staph infections, including MRSA, occur most frequently among persons in hospitals and healthcare facilities (such as nursing homes and dialysis centers) who have weakened immune systems, however, the manifestation of MRSA infections that are acquired by otherwise healthy individuals, who have not been recently hospitalized, or had a medical procedure such as dialysis, or surgery, first began to emerged in the mid- to late-1990's. These infections in the community are usually manifested as minor skin infections such as pimples and boils. Transmission of MRSA has been reported most frequently in certain populations, e.g., children, sports participants, or jail inmates.