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). 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.Plasmids, genetic elements that can be transferred from one bacterium to another, cause S. aureus to develop resistance to antibiotics. At least five types of genetic material (SCCmec genes I-V) have been identified. Hospital-acquired MRSA (HA-MRSA) usually have genes I-III while community-acquired MRSA (CA-MRSA) have genes IV-V. HA-MRSA is resistant to more antibiotics than CA-MRSA. These plasmids are strands of DNA, separate from the bacterial genome, which can self-replicate and frequently are responsible for the synthesis of compounds that cause antibiotic resistance in bacteria.
MRSA bacteria can be transmitted by direct (though skin and body fluids) and indirect contact (from towels, diapers, and toys) to uninfected people. Also, some individuals have MRSA on their body (on their skin or in their nose or throat) but show no symptoms of infection; these people are termed MRSA carriers (see above) and can transmit MRSA to others. Statistics show that CA-MRSA is the predominant MRSA type found in the population. Most carriers are best detected by culturing MRSA from nasal swabs.Symptoms of MRSA infections are variable; however, pus production is often found in the infected area. Classic examples of pus-containing areas in patients are boils (pus in hair follicles), abscesses (collections of pus), carbuncles (large abscesses with pus draining), sty (pus in an eyelid gland), and impetigo (pus in blisters on the skin). Cellulitis (infection under the skin or fatty tissue) usually does not have pus but begins with small red bumps on the skin, sometimes with itching, and also may be due to MRSA. Children and adults have many of the same symptoms; in children, often a group of them develop these symptoms in a close time span. The groups are often family members, close friends, children in a day care center, or members of an athletic team. The symptoms mentioned above are most often found in CA-MRSA but can also be found in HA-MRSA. When any antibiotic therapy fails, CA- and HA-MRSA should be considered as a potential cause of infection.
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