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MRSA Infection
(Methicillin-Resistant Staphylococcus aureus) Infection

MRSA Infection Overview

MRSA is the abbreviation for methicillin-resistant Staphylococcus aureus. Staphylococcus is a group of bacteria, familiarly known as Staph (pronounced "staff"), that can cause a multitude of diseases as a result of infection of various tissues of the body. Distribution of S. aureus is worldwide: As many as 11%-40% of the population is estimated to be colonized. However, in 1959, methicillin, an antibiotic closely related to penicillin, was introduced to treat Staphylococcus and other bacterial infections. Within one to two years, Staphylococcus aureus bacteria (S. aureus) started to be isolated that were resistant to methicillin. These S. aureus bacteria were then termed methicillin-resistant. MRSA usually show resistance to many antibiotics.

Because MRSA is so antibiotic resistant, it is termed a "superbug" by some investigators. This superbug is a variation of an already recognized human pathogen, S. aureus, gram-positive bacteria that occur in grape-like clusters termed cocci. The bacteria are usually found in the human armpit, groin, nose (most frequently), and throat. Fortunately, only about 1%-2% of people are colonized by MRSA, usually in the nose, according to the U.S. Centers for Disease Control and Prevention (CDC). In the majority of cases, the colonizing bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body and lead to infection; because of its ability to destroy skin, it is also one of the types of bacteria that has been termed a "flesh-eating bacterium."

MRSA are not VRE organisms (VRE means vancomycin-resistant Enterococcus species). Enterococci are bacteria that occur in the intestine. However, a strain of MRSA can be resistant to the antibiotic vancomycin (Lyphocin, Vancocin HCl, Vancocin HCl Pulvules) and these strains are termed VRSA (vancomycin-resistant Staphylococcus aureus). Plasmids (extra-chromosomal genetic material) that code for antibiotic resistance can be transferred between these two bacterial types and other types of bacteria such as Escherichia (E. coli</i>). Also, the lay press has occasionally labeled MRSA as a virus; this is a mistake but people still report it from time to time so don't be confused if the term MRSA virus reappears, as it will be corrected in most instances.

Even without antibiotic resistance, S. aureus has effective means to cause infections. Bacterial strains of S. aureus can produce proteolytic enzymes (enzymes that break down proteins resulting in pus production), enterotoxins (proteins that cause vomiting, diarrhea and in some cases, shock), exfoliative toxin (a protein causing skin disruption, blisters), and exotoxin TSST-1 (a protein that can cause toxic shock syndrome). Adding antibiotic resistance to this long list of pathogenic mechanisms (ways to cause infection) makes MRSA a formidable superbug.

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Read What Your Physician is Reading on Medscape

Staphylococcal Infections »

Staphylococcal infections are usually caused by the organism Staphylococcus aureus.

Read More on Medscape Reference »


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