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What is methicillin-resistant Staphylococcus aureus (MRSA)? (Continued)

A deadly complication of MRSA is a deep infection, necrotizing fasciitis, which causes rapid spread and destruction of human tissues. Some but not all strains of MRSA are more likely to behave like "flesh-eating bacteria." It is impossible to predict which MRSA infection will be "flesh-eating."

How many strains of MRSA are there?

In general, there are two major strains of MRSA, "community-acquired” or CA-MRSA and "hospital acquired" or HA-MRSA. CA-MRSA differs from HA-MRSA in that it is often resistant to fewer antibiotics and it is by definition picked up outside of the hospital or health care institution. CA-MRSA strains are often able to cause more severe and deeper infections in healthy people than HA-MRSA. They often have a variety of "virulence factors" that are responsible for this. Some of these are "leucocidin" proteins that are toxic to immune cells that fight infections or cause more inflammation and tissue damage; Panton-Valentine leucocidin (PVL) protein is a well-known example that is produced by the USA300 strain of CA-MRSA. The "phenol-soluble modulin" (PSM) proteins are a recently discovered class of leukocidins that increase the likelihood of causing severe disease in various ways.

Most HA-MRSA infections have been due to the USA100 strain. HA-MRSA is more likely to affect people in health care institutions who may have weaker immune systems due to other illnesses. HA-MRSA is less likely to cause problems for healthy people in the community.

Reviewed on 6/30/2017

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