Killer bacteria on the loose; are we about to lose the war on microscopic invaders.

The scene: You wake up for the sixth day in a row with a horrible sore throat. Your tonsils are so swollen you can hardly swallow. Turning on the television, you hear a horrifying report: People all over the city are dying from a type of strep throat that can no longer be treated with drugs.

A nightmare, yes. But it's one that some scientists say could come true. Some bacteria, the microbes that cause many diseases, are developing resistance to antibiotics, the drugs designed to kill them. Last year, according to the Centers for Disease Control and Prevention, more than 70,000 people died from infections caused by these antibiotic-resistant "bugs."

And these dangerous, drug-resistant microbes are spreading their resistance to other bacterial species. One type of blood-poisoning microbe, Staphylococcus aureus, has strains that are resistant to all but one antibiotic. If those staph strains become resistant to that drug too, "we'll have people dying of very standard bacterial infections," says Dr. Stuart Levy, a microbiologist at Tufts Medical School in Boston. The question, says Levy, is "Can we come up with new drug before then?"

We haven't always had drugs to fight infections. In the 19th century, millions of people died from bacterial diseases such as pneumonia, meningitis, and scarlet fever. But in 1928, British scientist Alexander Fleming discovered a substance produced by a mold that could kill harmful bacteria. This first antibiotic, penicillin, soon became the miracle drug of the 20th century.

By the mid-1980s, doctors had so many antibiotics at their disposal, many didn't give bacterial diseases a second thought. If one drug didn't work against a particular bug, they'd simply try another. They never dreamed the drugs would stop working.

EVOLUTION REVOLUTION

But as it turns out, doctors' willingness to prescribe antibiotics has helped the bugs that are resistant to these drugs survive--and thrive. Here's how:

When bacteria infect your body, they are constantly dividing. Before each division, they duplicate their DNA (genetic material) so that each "daughter" cell gets a copy. But with each duplication, there's a chance of a mutation--a slight copying error that will give one daughter bacterium a new trait.

"There's maybe a one in a million chance that a mutation will allow a bacterium to resist an antibiotic," says Michael Starnbach, a microbiologist at the University of Washington School of Medicine in Seattle. But bacteria multiply by the billions, he says. Some produce three generations of offspring in an hour! So one in a million isn't that rare.

When a bacterium does develop antibiotic resistance, it doesn't have an immediate advantage over its fellow microbes, Starnbach notes. But when the antibiotic comes flowing through your bloodstream, the drug kills off all the competition--all the other microbes looking for nutrients and a place to live. The resistant strain, the sole survivor, is then free to reproduce unchecked. And with each division the bug passes its drug resistance to its descendants. Soon, your whole body is infected with a strain the drug cannot kill.

INFECTION CONNECTION

What's worse, says Starnbach, is that antibiotic-resistant bacteria can spread from person to person. The drug these bugs are resistant to won't work in any of these infected people.

Plus, the microbes can pass their resistance genes to bacteria from other species (see diagram, below). The result: new kinds of resistant strains.

"For a while, we were able to keep up with resistance," Starnbach says. "There were drugs being developed quickly enough that we could take care of the problem. But now, the organisms are outpacing the technology."

THE BATTLE AHEAD

Is there any way to avoid a return to the deadly bacterial epidemics of the past? Starnbach and Levy give several suggestions:

* When your doctor prescribes antibiotics, ask why. Antibiotics won't cure colds and flus, which are caused by viruses. If taken when not needed, antibiotics could turn your body into a breeding ground for any drug-resistant bacteria lurking there.

* Finish all antibiotic prescriptions, as directed. If you don't, the most hardy bacteria could be left behind to reproduce and pass on their resistance.

* Avoid spreading infections. For example, don't share toothbrushes, drinking glasses, or other objects that can easily spread germs. And cover your mouth when you sneeze.

* Join the battle: Become a microbiologist and work to develop new, effective drugs and vaccines.

"Half the drug companies making antibiotics six years ago aren't anymore," says Levy, "because they thought they had in the game." The rise of drug-resistant bugs, he says, proves there's more work to be done.