Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
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
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
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
Symptoms of a MRSA infection depend on where the infection is. If MRSA is causing an infection in a wound, that area of your skin may be red or tender. If you have pneumonia, you may develop a cough.
Community-associated MRSA commonly causes skin infections, such as boils, abscesses, or cellulitis. Often, people think they have been bitten by a spider or insect. Because MRSA infections can become serious in a short amount of time, it is important to see your doctor right away if you notice a boil or other skin problem.