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Methicillin-Resistant Staphylococcus Aureus Infections

Information about MRSA Infections

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Updated July 03, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

The bacteria, Staphylococcus aureus, normally lives on the skin and sometimes in nasal passages. It's the most common cause of skin and soft tissue infections in most countries of the world. There are many strains of S. aureus in the world today, but an important, evolving strain is Methicillin-resistant Staphylococcus aureus (MRSA). MRSA is not killed by the typical antibiotics that kill S. aureus.

Staph Skin Infections

S. aureus causes skin infections like: Normally these infections are treated with a group of antibiotics called β-lactam antibiotics, but these antibiotics don't kill MRSA. Examples of β-lactam antibiotics include:
  • Penicillins like benzathine penicillin, nafcillin, and dicloxicillin
  • Cephalosporins like cephalexin, cefuroxime, and ceftriaxone
  • Monobactams like aztreonam
  • Carbapenems like imipenem

Where Did MRSA Come From?

S. aureus, like many bacteria, has the ability to mutate to survive. As the bacteria has been exposed to antibiotics, there have been tiny, incremental changes in the DNA of the bacteria that allow it to adapt and survive. Certain strains of the same bacteria develop that have different properties and different adaptations. MRSA has been traced back to a strain in the 1950s called phage type 80/81 that was known for its ability to cause serious infections.

MRSA Types

MRSA has been divided into two different types:
  • CA-MRSA: Community-aquired MRSA
  • HA-MRSA: Hospital-acquired MRSA
In general HA-MRSA is the more serious of the two sub-types. However, it's difficult to pin down the facts about the differences between these infections because there are different definitions of the sub-types, and because of the nature of bacterial resistance, the sub-types themselves are changing.

MRSA Diagnosis

The definitive way to diagnose a MRSA infection is to perform a bacterial culture on pus from an infected wound. At times culturing the fluid from the inside of the nose is done to determine if a person is a carrier of the bacteria.

MRSA Treatment

For minor skin infections sometimes the only treatment needed is to drain the pus. This is called an I&D, or incision & drainage. Drainage is also used for more serious infections along with antibiotics that are used to kill the bacteria. There are antibiotics that treat MRSA, but resistance to some of these antibiotics is starting to develop in some areas. Sometimes a combination of antibiotics is used to prevent further resistance from developing. Antibiotics that are typically used include:
  • trimethoprim-sulfamethoxazole (Septra or Bactrim)
  • clindamycin
  • linezolid
  • tetracycline
  • vancomycin

Prevention of MRSA Infections

Personal hygiene measures are the key to preventing MRSA infections. There are certain risk factors for developing MRSA infections and knowing what these are can help you avoid those situations. Specific guidelines to follow include:
  • Cover actively draining wounds
  • Don't touch another person's wounds
  • Don't share personal objects like towels and razors
  • Clean hands regularly using antibacterial soap or alcohol-based gels

Sources:

Gould, IM. “Antibiotics, skin and soft tissue infection and methicillin-resistant Staphylococcus aureus: cause and effect.” Int J Antimicrob Agents. 34 Suppl 1(2009): S8-11.

Kil, EH et al. “Methicillin-resistant Staphylococcus aureus: an update for the dermatologist, Part 2: Pathogenesis and cutaneous manifestations.” Cutis. 81(2008): 247-54.

Miller, LG, and SL Kaplan. “Staphylococcus aureus: a community pathogen.” Infectious Disease Clinics of North America. 23(2009): 35-52.

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