Resistance at the cellular and biochemical levels

In the preceding sections, I talk about antibiotic resistance in general terms: how bacteria can evolve through mutations and through gene transfer. Whether resistance is conferred by mutations in DNA or by gene transfers, something goes on at the cellular and biochemical levels that changes the bacteria from being antibiotic sensitive to being antibiotic resistant. Basically, the resistance comes in one of three forms:

i Mutations that reduce the amount of antibiotic entering the bacterial cell, such as changes in the cell membrane that make it more difficult for the antibiotic to get in or that pump out the antibiotic as soon as it gets in.

i Mutations that enable the bacteria to produce enzymes that destroy the antibiotic.

i Mutations that change what the antibiotic targets. These changes can range from changing the shape of proteins so that the antibiotic no longer recognizes them to reorganizing biochemical pathways to eliminate the stages that the antibiotic targets.

Mercy, mercy me! MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is a staph infection that can be very hard to treat because it's resistant to a lot of antibiotics including, no surprises here, methi-cillin, which otherwise would be wonderfully effective. According to the U.S. Centers for Disease Control and Prevention, MRSA infections (discovered in the early 1960s) accounted for 2 percent of staph infections in 1974. Thirty years later (by 2004), MRSA accounted for 63 percent.

MRSA is alarming for these reasons:

I Although MRSA staph infections can still be treated with other drugs, these drugs are more expensive, have greater side effects, and act more slowly than the drugs that were effective against it in the past. MRSA can often be treated with the antibiotic Vancomycin, for example. Unfortunately, we now have to worry about a new version of staph infection called, you guessed it, VRSA.

1 MRSA infections cause thousands of deaths every year, but the most frightening ones, the ones that make for the most sensational news, are the cases of "flesh eating staph." Deep bacterial infections can cause massive tissue damage. While many kinds of bacteria have been implicated in such infections, MRSA is becoming an increasingly common cause. Because of the speed with which these deep infections can progress, treatment becomes a race against time. Even with the best medical care, fatality rates can be high, and having to use suboptimal antibiotics (because bacteria have grown resistant to the better ones) only makes the situation worse.

1 Most MRSA infections (about 85 percent) are acquired in healthcare settings, but in the 1990s, MRSA began showing up in the broader community and are called CA-MRSA (for community associated MRSA).

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