Can you tell me anything about MRSA infection? My friend has fluid on her spine and the doctors are finding it hard to drain because it is so thick. They said she had a MRSA infection.

Linda

MRSA stands for methicillin-resistant Staphylococcus aureus (S. aureus). Methicillin is an antibiotic in the penicillin family. S. aureus is a very common bacterium and one of the principal agents of bacterial infection in humans. S. aureus infections include impetigo (which is also caused by strep bacteria), boils, carbuncles and deep abscesses. The bacterium is virulent and can spread to other areas of the body. It is one of the more common causes of bacterial endocarditis, a serious infection of the heart valves. It can spread to the joints, causing destructive infectious arthritis. It also commonly infects the bones, causing osteomyelitis.

Some simple skin infections caused by S. aureus can be treated with topical antibiotics or by draining the infection. More-invasive infections need to be treated with antibiotics. Endocarditis, arthritis, osteomyelitis and other deep infections such as your friend's spine infection must be treated with intravenous (IV) antibiotics, usually for several weeks.

When penicillin was first introduced, it killed S. aureus, and that antibiotic was the drug of choice for these infections. But soon strains of S. aureus appeared that could produce an enzyme that destroys penicillin molecules. However, the bacterium could still be killed with synthetic forms of penicillin that were resistant to the destructive enzyme. Such drugs include methicillin (trade name Staphcillin), oxacillin and nafcillin (trade name Unipen). Because methicillin is more toxic than the other two antibiotics, we do not use it very often, if at all.

Recently, many strains of S. aureus have developed resistance to the newer synthetic penicillins. Because methicillin is the antibiotic routinely used in the lab to identify this resistance, we call these strains "methicillin-resistant Staph aureus," or MRSA.

The importance of MRSA cannot be overstated. In addition to being resistant to all of the penicillin antibiotics, these microorganisms are also resistant to most of the other classes of antibiotics. The only antibiotic available in the United States with reliable activity against MRSA is vancomycin (trade name Vancocin). It is always worrisome when there is only one choice to treat such serious infections, and vancomycin also has some distinct disadvantages. First, the antibiotic can be toxic, and so blood levels generally need to be monitored. Second, it is only effective against S. aureus when given intravenously. Third, its activity against S. aureus infections is not as good as the penicillins. (Of course, against MRSA, the penicillins are not effective at all. However, the outcome of a MRSA infection is probably not as good as it would have been if vancomycin did not have to be used.)

Your friend has a spine infection with MRSA. All bone infections, including those due to MRSA, must be evaluated for any fluid collections (abscesses). In general, these abscesses need to be drained to provide any hope of curing the patient. In addition, your friend will need a long course, usually four to six weeks, of IV vancomycin. Her chance of cure is pretty good, though she may need further procedures to help drain the abscess and eradicate this serious infection.