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Science
Matters by David Suzuki
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 salmon in fish farms). 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.
To discuss this topic
with others, visit the discussion forum at www.davidsuzuki.org.
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