Food contamination isn't just a simple stomach ache anymore. Sixteen-month-old Anna Grace Gimmestad of Evans, Colorado, loved fruit juices. When she went grocery shopping with her mother, she would excitedly point to the colorful, fruity juices on the shelf.

In late 1996 little Anna fell ill after drinking some tainted apple juice. Within two weeks her kidneys failed, her heart faltered, and she died. The juice she drank was contaminated with one of America's increasingly troublesome pathogens: a strain of bacteria known as E. coli 0157.H7.

This deadly strain has been found in fresh-fruit juices and vegetables-ironically the very foods Americans desire most in their pursuit of good health. (Of course, this incident and some other relatively isolated instances by no means constitute sufficient grounds to cease buying these food products.)

E. coli infects as many as 20,000 Americans every year, mostly through meat, and about 500 die. E. coli 0157.H7 was first identified in food in 1980, and sporadic outbreaks have become increasingly more frequent.

Although the nation's food supply remains one of the safest in the world, it apparently is not good enough always to catch such virulent strains. Inattention to health safeguards can make the difference between life and death. Apparently the batch of apples that wound up in the juice little Anna Gimmestad drank had fallen to the ground and come in contact with deer feces. Safeguards that should have prevented this tragedy failed.

Is this an isolated incident, or are there other dangerous bugs that can intrude into our lives, breaking down the perceived wall of protection we assume that science and medicine have built?

Over the last year a series of troubling reports has described how microorganisms are fighting back, mutating into strains resistant to the most powerful antibiotics in the medical arsenal. Among them are such killers as tuberculosis, bubonic plague and staphylococcus (staph) bacteria.

The battle against the bugs

Just 15 years ago most staph infections responded to a wide range of antibiotics. But in the early 1980s a specific strain surfaced that medical practitioners found resistant to methicillin, then the drug of choice to combat the ubiquitous staph bacteria.

However, some strains of staph found ways to mutate around its killing properties, and today methicillin is useless against half of all staph infections. The omnipresent bug has developed resistance to other drugs as well. Because bacteria and viruses can mutate rapidly, researchers must constantly develop new antibiotics to stay one step ahead in effective treatments.

In recent years, however, such advancements have begun to stall. Vancomycin, the last antibiotic with a clear knockout punch against bacteria, is showing signs of faltering as new strains emerge. The notion that science has given us permanent victory over infectious diseases may prove to be illusory.

"We don't have any new drugs, really new ones, of the vancomycin type coming through in the next few years, and it concerns me that we're going to lose the one we can count on," said Stuart Levy, director of the Center for Adaptation Genetics and Drug Resistance at Tufts University Medical School in Boston.

An alarming development

A notable case illustrating the challenge medicine faces involved a patient from Michigan. His case might well prove a harbinger of more significant health problems ahead, according to public-health officials who noted that similar instances of drug resistance in previously susceptible bacteria have become more and more common around the world.

The Michigan patient became infected with a strain of Staphylococcus aureus, a common bacterium that manifests itself in ailments ranging from pimples and boils to fatal septic infections in surgical patients. Because of kidney failure, this patient relied on a home dialysis system to cleanse his blood in place of his failed kidneys. The procedure required a tube to remain in the patient's abdomen. Since this process makes patients prone to frequent infections, treatments with vancomycin were used to control and eradicate occasional staph infections.

However, in this case the miracle drug proved less effective than usual. Tests done and confirmed by the Centers for Disease Control and Prevention (CDC) revealed that this newly discovered strain of bacteria had developed the ability to survive moderate levels of vancomycin given intravenously. Although a previous single case was recorded in Japan, this was the first time vancomycin-resistant staph had been discovered in the United States.

The problem of overprescribing

William Jarvis, epidemiologist and acting director of the CDC's hospital infection program, thinks that this drug-resistant strain of staph has developed largely because of doctors overprescribing vancomycin when less-potent drugs would have sufficed. The more a strain of bacteria comes into contact with a given antibiotic, he explained, the more opportunities it has to develop a way to resist that drug's effects.

"It's become common practice in some dialysis centers that if a patient develops a fever or pain at the catheter site or some other nonspecific symptom, they'll give them a bolus of vancomycin," he said. "That practice has clearly got to stop. We have recommended that, . . . if it is susceptible to other antibiotics, then we must use those instead."

Dr. Jarvis is concerned not just with the overprescribing of vancomycin and other antibiotics, but with the lack of funding necessary for state and local laboratories to track the emergence of resistant bacteria.

Anthony S. Fauci, chief of the National Institute of Allergy and Infectious Diseases, defends the use of vancomycin in cases in which seriously ill patients need to be treated immediately. In such serious cases "you don't want to take a chance and you have to go with your big guns," he said. Dr. Fauci indicated that, if subsequent testing shows a lesser drug will work, then in many cases the patient can be safely switched to a less-potent drug. This reserves vancomycin for emergencies.

For the first time in the history of the United States, scientists have found a strain of staphylococcus bacteria that can resist treatment with vancomycin. Up until recently this superpowerful antibiotic proved 100 percent effective against this threatening microbe.

Many doctors are now placing their hope in Synercid, a new antibiotic developed in France. But even this drug is no silver bullet against infections; in some studies it has not proved as effective as existing antibiotics.

The regular mutation of bacteria and viruses is what makes development of effective treatments and vaccines against HIV, the virus that causes AIDS, so maddeningly difficult. The virus has so far been able to mutate at a rate faster than researchers can develop weapons with which to fight it. By the time treatments are devised, tested and put into use, new strains have emerged that are resistant to those treatments.

Stemming antibiotic resistance

There are some encouraging signs in the battle against drug-resistant microbes. If doctors and patients change their behavior, they may be able to slow the spread of drug-resistant bugs. Finland has noted a favorable change in human behavior and a corresponding reduction in antibiotic-resistant bacteria. Similarly, New York has noted a dramatic drop in the frequency of drug-resistant tuberculosis after adopting a newly revitalized tuberculosis-control program.

But we might be surprised how much people have come to depend on antibiotics to cure their illnesses. In the United States one fourth of Streptococcus pneumoniae bacteria (which cause ear infections, pneumonia and meningitis) are resistant to penicillin. Longer hospital stays and higher mortality rates are associated with resistant organisms, especially in hospitals.

Experts warn that, if vancomycin resistance develops in the common staph bacteria, it will precipitate a monstrous medical problem. "I think it's important to be aware of this before we do reach the end of the rope," said Morton N. Schwartz, professor of medicine at Harvard Medical School.

Doctors and patients aren't the only ones who must consider the overuse of antibiotics. Fully 40 percent of the antibiotics produced in the United States in the early 1980s was given to livestock. Fruit growers also use such potent drugs. Of the 15,700 tons of antibiotics produced in that period, 300,000 pounds were sprayed on pears, apples and other fruit, ostensibly to prevent a blight that causes scaling on fruit skin.

"We are just covering the world with this thin layer of antibiotics, which is selecting out [bacterial] resistance," said David L. Heymann, director of the World Health Organization (WHO) division on emerging diseases.

Drugs change the environment of bacteria, killing sensitive strains and providing a survival advantage for germs whose genetic traits permit them to withstand and overcome potent antibiotics. Eventually each individual and society are at greater risk. Thus we can understand why some observers feel that antibiotics should be used more sparingly.

The Centers for Disease Control and Prevention estimate that more than 50 million of the 150 million antibiotic prescriptions written annually for patients outside of hospitals are not needed. Eliminating unnecessary prescriptions could greatly reduce the ability of bacteria and viruses to develop resistance to drugs.

Experts urge this change of human behavior in an effort to stem the rising tide of antibiotic resistance. Otherwise we might be creating a specter that can come to haunt us, the likes of which mankind hasn't experienced since the plagues that wiped out much of the world in the Dark Ages. GN