How To Recognize And Treat Community-Acquired MRSA
In the past few months, we have heard numerous reports in the news about a “new super bug” that is resistant to conventional antibiotics and is sweeping through high school sports locker rooms and classrooms. The alleged new super bug is methicillin resistant Staphylococcus aureus (MRSA) and, more specifically, community-acquired MRSA (CA-MRSA).
However, MRSA is not a new type of bacteria that has suddenly appeared in the community. The organism has actually been around for quite a few decades.
In 1941, all S. aureus isolates were susceptible to penicillin and relatively low doses of penicillin (PCN) were required to treat it. However, by 1944, penicillin resistant strains were identified in both hospitals and the community. Around this same time, physicians saw the emergence of semisynthetic PCNs including methicillin, nafcillin and oxacillin. These became the antibiotics of choice for Staph infections. However, Staph aureus soon developed resistance to these semisynthetic penicillins. The first strain of MRSA was identified in 1961 and became prevalent by the late 1970s. In the 1980s, sporadic cases of CA-MRSA emerged in previously healthy children and young adults having no recent contact with hospitals or other healthcare settings.1
Indeed, CA-MRSA is not a new pathogen that has suddenly begun to run rampant throughout our communities, schools and athletic facilities. In fact, the CDC reports that approximately 30 percent of healthy, asymptomatic individuals and as many as 65 percent of people with Staph skin infections carry S. aureus in their anterior nares and skin. Approximately 1 percent of the population is colonized with MRSA via skin and nares.2,3
Indeed, CA-MRSA has presented an interesting public health issue regarding the epidemiology, treatment methods and prevention of this infection in the community. It also presents an interesting dilemma to physicians regarding the most efficacious ways of recognizing and treating CA-MRSA.
Differentiating Between CA-MRSA And HA-MRSA
According to the Centers for Disease Control and Prevention (CDC), CA-MRSA infections are MRSA infections that are acquired by people who have not been recently (within the past year) hospitalized or had a medical procedure such as dialysis, surgery or catheter placement.
Staph aureus is a gram-positive coccus that grows in clusters. Some S. aureus isolates have developed resistance to the semisynthetic penicillins, namely methicillin, by altering the antibiotic’s target, penicillin binding protein (PBP), a protein on the bacterial inner membrane. This alteration leads to a decreased affinity for the antibiotic and what we know as MRSA.1
The genes for resistance of CA-MRSA are typically carried on the mec Type IVa chromosomal cassette, a mobile genetic unit.4 This gene cassette codes only for methicillin resistance as opposed to multiple antibiotics. This is a major characteristic that distinguishes CA-MRSA from hospital-acquired MRSA (HA-MRSA). Therefore, CA-MRSA, as opposed to HA-MRSA, remains highly susceptible to many antibiotics.5 In fact, CA-MRSA clones are genetically distinct from isolates of HA-MRSA and are actually more similar to methicillin sensitive Staph aureus on a genetic level.6