En español | When it comes to infectious bacteria, it's us versus them: survival of the fittest. Unfortunately, human activities have helped create some bacteria that are very fit indeed. These so-called superbugs have adapted to and survived the most powerful weapons we have to combat them — antibiotic drugs.

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Micrograph of the rod-shaped bacteria "Klebsiella pneumoniae," the new superbug. — Tony Brain/Science Photo Library

The problem isn't confined to hospitals. Garden-variety infections of the ear, urinary tract, skin and lungs are increasingly taking stubborn forms that require more antibiotics or a combination of drugs to cure.

Age-old afflictions such as gonorrhea and tuberculosis — curable for the first time in the 20th century thanks to antibiotics — are getting harder and harder to treat. New strains of one of the most well-known superbugs, MRSA — methicillin-resistant Staphylococcus aureus — are increasingly attacking healthy people outside health care facilities, causing mostly nasty and sometimes invasive skin infections, but also aggressive pneumonias.

Meanwhile, certain bacteria that tend to cause bloodstream and other infections in vulnerable hospitalized patients — bugs with exotic names like Acinetobacter baumannii and Klebsiella pneumoniae — are becoming more lethal, impervious to most or even all of the antibiotics in physicians' tool kits.

"For these cases," says Brad Spellberg, M.D., of the University of California, Los Angeles David Geffen School of Medicine, "we're back to dancing around a bubbling cauldron while rubbing two chicken bones together."

Such "pan-resistant" bacteria are still the exception, but they vividly illustrate what's at stake in attempts to stem the proliferation of drug-resistant bacteria. The latest figures from the U.S. Centers for Disease Control and Prevention (CDC) show that just one of these superbugs, MRSA, caused serious infections in some 82,042 Americans in 2010, killing 11,478. Older people are especially vulnerable if they contract a superbug.

Antibiotics are a cure, and a cause

How have humans let the bugs get stronger? By saturating our environment with antibiotics, the very miracle drugs we created to fight bacterial infection. Some 7 million pounds of antibiotics are sold for human use each year, while 29 million pounds are sold for use in animals, mostly food animals. This, many experts argue, represents gross overuse of the drugs, and only makes it less likely they'll work when we need them most.

Bacteria exist in teeming numbers, reproduce rapidly and can pass genetic traits — including resistance to antibiotics — not only to succeeding generations but also to other bacteria in their environment. The more bacteria encounter an antibiotic, the more readily they spawn hardier versions of themselves capable of overcoming the drug.

Inappropriate prescriptions for coughs and colds represent "the number one problem area," says Ralph Gonzales, M.D., who researches antibiotic use at the University of California, San Francisco. "Respiratory infections account for 60 or 70 percent of all antibiotics prescribed in the outpatient setting," he says. "At best, one in five of those infections needs antibiotics." The great majority are due to viruses, not bacteria. Antibiotics have absolutely no effect on viruses. Some patients want an antibiotic even if there's only a small chance it will help, and studies show doctors often acquiesce. Then, rather than take the full course of antibiotics as prescribed, some save pills to use later or share. This may allow germs to persist, develop resistance and come roaring back.

Next: "Antibiotics are sometimes given when they aren't needed." »