Published: March 07, 2007 09:23 pm            

Ask the Doctor: Infection adapts to human resistance

TERRE HAUTE — “My sister-in-law ended up with a Mersa infection that she had to take antibiotics for, for six weeks. The interesting thing is that she hadn’t been in the hospital first, which is where I thought you had to be to get exposed to that. So, where else would it come from?”

Methicillin-resistant staphylococcus aureus, or MRSA, is the bacteria you mention with your sister-in-law. It is very common in our environment and not just found in hospitals anymore. Around 30 percent of all people in the United States have staph in their noses.

Most of the bacteria does not cause infection because it stays outside our skin. Once staph bacteria get through the skin and find a warm, moist environment with plenty of nutrients, they reproduce, leading to an infection. People with healthy immune systems are usually able to control the infection, but in people with a decreased immune function, staph can rapidly become a problem requiring medical intervention.

Now add into the mix strains of staph that have developed resistance to some of our most commonly used antibiotics, known as Methicillin-resistant Staph aureus (MRSA), and we have a much more complex problem.

Over the years, bacteria have accumulated a variety of genetic mutations that give them some resistance to antibacterial compounds.

Historically, it was always an advantage to the bacteria to have these mutations since there are a number of naturally occurring antibacterials in the world. Remember, penicillin was first discovered in bread mold.

What has happened in recent times is that humans have increased the amount of antibiotics in the environment by several fold.

The most common path to antibiotic resistance is that a bacterial population is exposed to an antibiotic for a short time. This short exposure kills the bacteria that do not have any resistance genes, leaving behind the ones that do.

One of the normal processes of bacterial life is the ability to share DNA with other bacteria. So now the pool of bacteria that have survived the antibiotics, start to share DNA and mix the resistance genes up and pretty soon you have a population that is much more resistant to the antibiotic.

When a patient gets a prescription for a week’s worth of antibiotic but stops taking it after three days because they feel better, they have added to the problem of antibiotic resistant bacteria. When a patient has a viral infection like a cold, then takes antibiotics that a friend had left over, they have added to the problem.

In past years, the most common place to see MRSA was in the hospital. This is not because hospitals are dirty places, but because hospitals are the place where you are most likely to have something done that takes the staph you carry with you all the time and gets it into that nice warm environment inside your skin. So hospitals and health care facilities are where you find the most staph infections because they have the highest density of sick people as well.

As recently as 1980, less than 5 percent of all staph infections in hospitals were MRSA. This has steadily risen so that now nearly 60 percent of staph infections in intensive-care units were MRSA.

There has also been a recent increase in MRSA infections that are acquired in a non-hospital setting. Known as community-associated or community-acquired MRSA, this is becoming a significant problem. Some of these infections are caused by MRSA strains that are not found in the hospital population and may spread more easily than the hospital strains.

There have been documented outbreaks in correctional facilities, in athletic clubs and football and wrestling teams with MRSA.

You are still at risk for a staph infection in the hospital, but outside the hospital you also face the risk of getting an MRSA infection doing your regular activities. Wash your hands!

        

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