MRSA, coined a superbug by the media, was until recently considered a hospital infection control concern but has now made its way into the community.
Opportunistic Pathogens
Staphylococcus aureus is a bacteria that can be found normally living on the skin, nasal passages and moist areas of the body. When Staphylococcus aureus finds an entry point into the body, such as a cut or wound, it is capable of causing infection.
Staphylococcus aureus is one of the most common hospital-acquired infections, often occurring following invasive procedures including surgery. Methicillin-resistant Staphylococcus aureus (MRSA) is a strain of Staphylococcus aureus that has developed resistance to an antibiotic often used to treat serious infections caused by Staphylococcus aureus.
Hospital-Associated MRSA
MRSA has become a infection control concern in the hospital environment. Although not everyone who comes in contact with MRSA develops infection, the risk of infection is greater in a hospital environment where there is a population of people who are generally more susceptible to disease because of compromised immune systems, invasive procedures where organisms can be introduced into the body, and exposure to organisms on the hands of healthcare workers.
Many people who “have” MRSA carry the organism in their nasal passages, groin area or intestinal tract without effect. However, because hospital strains of MRSA are resistant to multiple antibiotics (including methicillin) commonly used to treat a variety of infections, and because Staphylococcus aureus is a common cause of infection, the risk of developing serious infection involving MRSA has infection control practitioners scrambling to find ways to reduce the spread of MRSA within their facilities.
The discovery of MRSA in the community is also a concern and much debate and media attention has been devoted to the topic. Strains of MRSA that have been recovered from people in the community who have developed infection are different from the strains found in the hospital environment. In addition, the types of infection that the community associated strains cause are different from MRSA infections in healthcare facilities, and infections caused by non-methicillin resistant strains of Staphylococcus aureus.
Community Associated MRSA
Community associated strains of MRSA are most often only resistant to the class of antibiotics that includes methicillin. Although community associated strains of MRSA are generally not multi-drug resistant like most hospital associated strains of MRSA, they seem to be more likely to cause invasive disease than hospital associated MRSA strains.
Virulence Factors
The reason for the greater virulence of community associated MRSA strains in otherwise healthy people was thought to be caused by a virulence gene not commonly found in all strains of Staphylococcus aureus. The gene produces the Panton-Valentine leukocidin (PVL) toxin.
However last year researchers exonerated PVL toxin as the cause of increased virulence in community associated MRSA strains. Dr. Otto and his colleagues at the National Institute of Allergy and Infectious Diseases (NIAID) published a study in the journal Nature Medicine describing the compound phenol-soluble modulin (PSM), which they believe is the cause for the greater virulence of community associated MRSA strains.
Phenol-soluble modulin is a substance produced by community associated MRSA strains that attracts neutrophils, a type of immune system cell, and destroys them through a process called lysis (breaking open) allowing MRSA the run of the body.
Read more about Staphylococcus aureus and MRSA:
Staph and Methicillin Resistance: Superbug Infections
Methicillin Resistant Staph: Superbug Infections
