Monday, August 16, 2010

Bacterial Resistance

Medical Meanderings

The Monsters We Made

Although the Cold War is over, there is still an arms race going on. This arms race is with an invisible enemy who seems able to invent new defenses almost as fast as we can invent weapons. So far, we are winning the race on most fronts, but many experts predict that in the very near future, this won’t be the case. Our enemy may become impossible to kill.

Bacteria are quick learners. Alexander Fleming invented penicillin in 1928, and at first, many medical experts declared that the Era of Infectious Disease was over. Humanity had won the war against the germs. Now, almost 80 years later, penicillin is rarely used because so many bacteria are resistant to it. And its cousins, the cephalosporins. And erythromycin. And, and, and… There have even been reports in recent years of bacterial infections resistant to one of our most powerful antibiotics, vancomycin, which was one of our biggest weapons. The bacteria are learning, and they really like to share.

How does a bacterium “learn” to resist penicillin, or any other antibiotic? There are several ways. In all cases, bacterial resistance is a wonderful example of evolution in action. There is a population of, say, a million bacteria. In that million, there may only be one that, by chance, has a slight mutation of its genetic code that changes protein X in its microscopic body. However, it just so happens that protein X is the target for an antibiotic. The antibiotic is introduced, and most of the million are killed by it, but that one mutant survives, because it alone is unharmed by the antibiotic. The survivor starts to reproduce, and soon we have a population of a million bacteria that can resist the antibiotic.

Humans, of course, aren’t stupid. We have invented countermeasures that can overcome bacterial resistance, brand new antibiotics that have new targets, and we’ve learned to use combinations of antibiotics together. Although we’re not stupid, sometimes we aren’t wise. We give millions of pounds a year of antibiotics to cattle to enhance their growth. We give antibiotics to millions of people each year who have only a cold or viral bronchitis, which antibiotics cannot touch. We make antibacterial soaps to fight imagined contamination. We’re giving the bacteria every chance we can to learn how to fight back.

Because they are such quick learners, many of our old enemies are coming back. We thought, for example, that we had defeated tuberculosis. Now, in many countries, treatment of tuberculosis requires three different drugs given together for several months. Many of our hospitals in America (including our own) fight MRSA, methicillin-resistant staphylococcus aureus, a difficult-to-treat common germ. Bacterial resistance is a fact of life now, and our enemies will not unlearn what we have taught them. We can only hope to stay a step ahead.

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