Misuse of antibiotics must be curtailed

August 2, 2002 - More than a quarter-century ago, I did a television program that discussed the hazards of misusing antibiotics, including using antibiotics as growth-promoters in livestock. Today, this practice continues in much of the world even though it has been implicated in the rise of antibiotic resistance, which can make some of our most powerful drugs useless.

Antibiotics are an extremely important tool in modern medicine. In the 1940s I came down with pneumonia and was close to death when a doctor injected me with penicillin. It was like a miracle - the next day I was up and out of bed. Antibiotics have saved countless lives by repelling bacteria. But bacteria evolve quickly and can become resistant to our drugs. So we create new drugs. Then the bacteria evolve again. Some have now evolved to the point that they are resistant to all of our drugs - they have become "superbugs."

In July, the most recent superbug, a type of Staphyloccocus aureus, was found in an American patient suffering from a leg ulcer. S aureus is actually a common bacteria often found in healthy people, but it can sometimes lead to severe infections. In this case, doctors tried several different antibiotics, but to no avail. Their last resort was a powerful antibiotic called vancomycin. To their surprise, it had no effect. An older drug eventually managed to stop the infection, but the patient was lucky to survive.

Although doctors have been expecting this to happen eventually, finding such a resistant strain of a common bacteria was disturbing. Fifteen years ago, doctors discovered a vancomycin-resistant strain of the common stomach bacterium Enterococcus, and it now plagues the intensive-care sections of hospitals. S aureus has the potential to be a much bigger problem.

A number of practices hasten the development of antibiotic resistance, including over-prescribing by doctors, failure to follow the required dosage regime and using the drugs to promote growth and reduce illness in livestock. These practices invariably speed up evolution by strongly selecting bugs resistant to antibiotics.

The European Union has banned the use of antibiotics in animal feed, but it is still permitted in North America. According to the Union of Concerned Scientists, more than half of the antibiotics in the U.S. are used for agricultural purposes (which includes farming fish like salmon). This indiscriminate use of antibiotics can lead to resistant infections in humans in two ways. First, people can become infected with resistant bacteria by direct consumption of meat containing a resistant pathogen like Salmonella. The U.S. Food and Drug Administration estimates that every year up to 10,000 Americans develop antibiotic-resistant infections from eating chicken containing such bacteria. Second, resistant bacteria found in food animals can transfer resistance to normally harmless bacteria in humans through physical contact. These common bacteria are persistent and may spread from person to person. Occasionally, they can cause infections, and if the bacteria are resistant to antibiotics, the infection may prove difficult to treat.

Recently, a group of U.S. scientists developed a mathematical model to examine how feeding antibiotics to livestock can lead to resistance. Their findings, published in the Proceedings of the National Academy of Sciences indicate that giving animals massive doses of antibiotics that are also used for humans reduces the useful life span of the drug by about 30 per cent.

Importantly, they also conclude that allowing antibiotics to be used in agriculture until resistant strains are discovered will not likely be effective "because once antibiotic-resistant bacteria are detected, much of the damage has been done." They recommend that if antibiotics are to be used in agriculture as growth promoters at all, then only those that have ceased to be helpful to humans should be used.

Researchers are hard at work developing new antibiotics. Recent breakthroughs, including the sequencing of the genome of an important bacterium and the discovery of a key to antibiotic resistance in one of the superbugs, are promising advancements. But unless we stop the rampant misuse of antibiotics, the effectiveness of new drugs will continue to be compromised.

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