|
Facts of the Matter
Richard Brill
|
Antibiotic overuse causing bug crisis
FOR CENTURIES, people have applied various preparations derived from living matter to combat infection.
The concept that one microorganism is capable of destroying one of another species was not conceived until Pasteur noted the antagonistic effect of certain bacteria on the anthrax organism and pointed out late in the 19th century that this action might be put to therapeutic use.
Pasteur's pupil Paul Vuillemin coined the term "antibiosis" in 1889 to mean a process by which life could be used to destroy life.
Meanwhile, German chemist Paul Ehrlich came up with the idea of selective toxicity: There might be certain chemicals that would be toxic to some organisms, such as infectious bacteria, but would be harmless to other organisms such as humans.
There were repeated hopes for a wonder drug after pyocyanase, a weakly effective antibiotic, was marketed from the late 19th century into the 1930s.
Until the 1930s there was no chemical treatment that could fight bacterial infections in general, and prevention was the main means of protecting patients from infections.
In 1928, Sir Alexander Fleming, a Scottish biologist, observed that Penicillium notatum, a common mold, had destroyed staphylococcus bacteria in culture. Although promising, it seemed impossible to extract the active compound intact from the yellow liquid produced by the mold.
In 1939, American microbiologist Rene Dubos showed that a soil bacterium could render pneumococcus bacteria harmless so they could not cause pneumonia.
Dubos then found a microbe in soil from which he obtained a product, tyrothricin, that was highly toxic to a wide range of bacteria. Unfortunately, tyrothricin was also toxic to red blood and reproductive cells in humans, so it could be applied as an ointment but not taken internally.
Penicillin was finally isolated in 1939 by Ernst Chain and his boss, Howard Florey, at Oxford University. In 1944, American microbiologists Selman Waksman and Albert Schatz isolated streptomycin and a number of other antibiotics from Streptomyces griseus bacteria.
The potential for antibiotic resistance was first raised in the late 1940s. Policy-makers and microbiologists responded by restricting the use of antibiotics through the prescription system and by the development of more robust drugs. Yet the warnings were discounted by grateful patients and hurried practitioners as antibiotics were overprescribed and improperly administered.
In the late 1960s, U.S. Surgeon General William Stewart declared that with the development of antibiotics and vaccines, infectious diseases had been conquered. It was not until the 1990s that the emergence of resistant bacteria was widely accepted as a global threat to be taken seriously.
There's a superbug crisis brewing, and it's caused by the overprescription of antibiotics. Doctors are seeing more and more patients with infections that are caused by bacteria that cannot be killed by the usual antibiotics. The answer, say medical researchers, is to come up with yet more antibiotics.
There is special concern over two notable superbugs.
One is enterococci bacteria that have become resistant to vancomycin, a so-called last-ditch antibiotic. There are no reliable alternatives, and there is fear that the gene that is responsible for the resistance in the enterococci could spread widely to more common bacteria, such as staphylococci.
The bacterium Staphylococcus aureus is known for its ability to develop resistance to most classes of antibiotics soon after they enter widespread clinical use. Vancomycin can stop many of these multidrug-resistant strains, but some bacteria that are closely related to S. aureus, which often causes life-threatening infections in hospital settings, can fend off vancomycin, prompting concerns that soon S. aureus will, too.
There has been at least one instance of a vancomycin-resistant strain of S. aureus in which the gene responsible for its invulnerability jumped to it from another species of bacteria.
In 2002 a vancomycin-resistant staph was cultured from foot ulcers on a patient in a Michigan hospital. The Center for Disease Control and Prevention analyzed the microbe and determined that the responsible gene had come from another bacterial species present in the patient's ulcer.
The researchers tested whether this S. aureus strain could transmit its resistance to other types of staphylococcus and found that it was indeed transferable, reinforcing concerns of potential widespread resistance.
The second concern is the appearance of multidrug-resistant tuberculosis. Tuberculosis spreads easily and is deadly. It is the leading cause of death by infectious disease worldwide. Treatment success drops from nearly 100 percent for the older strains to barely half that for the drug-resistant ones.
A number of antibiotics are effective against tuberculosis. Tuberculosis bacteria are very slow-growing, so antibiotics must be taken for six months or longer. Treatment must be continued long after the person feels completely well, or the disease tends to relapse because it was not fully eliminated.
To treat tuberculosis, two or more antibiotics are always used because treatment with only one drug can leave behind a few resistant bacteria, so people treated with only one drug develop tuberculosis that is resistant to that drug. A third and fourth drug are often used during the initial, intensive phase of treatment to shorten the duration of treatment and to ensure success even if there is drug resistance at the outset.
A new super-strain of tuberculosis is now prevalent in Eastern Europe, large areas of Russia and Southeast Asia. Unlike traditional TB, which still claims 2 million lives a year but is curable with the right drugs, the new bacterium has proved resistant to all known medicines.
According to professor Hugh McGavock from the University of Ulster in England, a specialist in prescribing medicine, the dark days before penicillin could be back within a decade. He has estimated that by then all antibiotics could be ineffective.
He notes that bacteria mutate every 20 minutes, and they can develop resistance to drugs in mere weeks.
Not all doctors agree with McGavock. Critics say measures are in place to tackle the resistance to antibiotics to make sure a crisis does not materialize. They say that new types of antibiotics are being developed that make it tougher for bugs to become immune to because they work in the same way as many of the methods that the body itself uses to ward off bacterial infections.
Richard Brill, professor of science at Honolulu Community College (
home.honolulu.hawaii.edu/~rickb), teaches earth and physical science and investigates life and the universe. His column is published on the first and third Sundays of every month. E-mail questions and comments to
rickb@hcc.hawaii.edu
Richard Brill picks up where your high school science teacher left off. He is a professor of science at Honolulu Community College, where he teaches earth and physical science and investigates life and the universe. He can be reached by e-mail at
rickb@hcc.hawaii.edu.