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By Mary Losure
September, 2000
Part of MPR's Fighting the Superbug series
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RealAudio 3.0 |
For years, scientists have warned the misuse and overuse of antibiotics is causing some bacteria to become resistant to antibiotics. Antibiotics are the first line of defense against sicknesses caused by bacteria. If the number of resistant strains of bacteria continues to grow, illnesses once easily treatable with antibiotics could become incurable.
Bacteria can develop resistance in hospitals, and also on farms where animals are treated routinely with antibiotics. Now, resistant bacteria are starting to spread outward into the environment, into the nation's streams and rivers.
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"We're coming up to a very severe situation where several infections in humans are no longer treatable."
- Prof. John Bennett | |
John Bennett is the chairman of biology at nearby Clarke College, a small private school in Dubuque. Two years ago, as a summer project with one of his students, he began testing bacteria in these waters.
"I couldn't believe it," he says, "I thought something has gone wrong with this experiment, it can't be resistant to everything we have."
Bennett and his student found bacteria resistant to the antibiotic tetracycline in every stream they tested. Some bacteria were also resistant to as many as five other antibiotics.
"We're finding bacteria that are resistant, not only to tetracycline, but to penicillin, ampicillin, choramphenicol, erythromycin, cefoxitin - key classes of antibiotics that are used for a broad range of treatment types. We're finding some bacteria that are resistant to every antibiotic that we've tested," Bennett says.
People don't drink this water, so it's unlikely the antibiotic-resistant bacteria in these streams will make people sick directly.
But Bennett says if a person wading in this stream accidentally swallowed just a drop, it could cause problems later.
"The bacteria at first might not make you sick, but when you get treated with an antibiotic, now you've got troubles. Because you've got bacteria in your system that will not respond. Not only that, these bacteria, they contain the genes, the genetic information necessary for resistance, and they can transfer these to other species of bacteria."
Imagine these genes spreading like dandelion seeds. The genes can pass from one bacteria to another in streams. From there, they can move into fish, birds, and other animals. One study found resistant bacteria in wild Canadian geese.
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Ash began his study in 1997. He says it was the first wide scale look at the problem.
"People have been aware that there might be antibiotic resistant bacteria out there, but no one really knew the extent of the damage," says Ash. "Our work clearly shows it might be neccessary to take some precautions in the future and to really acquire much more data on this."
There are several possible sources for the antibiotic resistant bacteria in rivers. Some strains of bacteria have naturally occuring resistance to antibiotics. Other resistant bacteria come from sewage treatment plants. Humans who carry resistant bacteria antibiotic resistant bacteria in their bodies can excrete them into waste. A third source is livestock operations.
Joseph Bumgarner is a researcher with the federal Environmental Protection Agency in North Carolina, a state with a large number of factory-style hog operations. He says livestock operations often use low levels of antibiotics as a growth promotant.
It's a process that fosters the growth of bacteria resistant to the specific drugs used.
"They're administered in sub-therapeutic doses, doses too low to effectively kill off all the enteric bacteria in the gut of the animal. So the survivors in the gut of the animal are probably the more resistant bacteria," says Bumgarner.
These resistant bacteria pass into manure, which is spread on farm fields and washed into streams and rivers. They also concentrate in manure storage basins.
When the basins rupture or flood, they can empty huge doses of bacteria into rivers.
That happened across North Carolina in 1999 during Hurricane Floyd. Asked how far or how fast the resistant bacteria are spreading, Bumgarner says no one knows.
"This is one of the things that we're attempting to start defining now with the studies that are already ongoing. There are just too many unknowns to reach any conclusions. The things that we do know are that number one, resistant bacteria are produced in this process, [and] the potential for them to escape into the environment is quite high. What the impact is once they enter the environment, that is an unknown for us right now."
Bumgarner says it's possible antibiotic resistant bacteria could harm fish and wildlife by altering the natural bacterial balances in their bodies. But he says the EPA needs much more information before it can figure out how to deal with the issue.
The spread of resistance genes into the environment is a newly-discovered wrinkle to the well known, growing problem of antibiotic resistance in general. This year the World Heath Organization issued a call for stronger action to combat antibiotic resistance worldwide.
Back in Iowa, biology professor John Bennett has studied the scientific literature documenting the growth of antibiotic resistance. Like many other scientists, he's deeply worried.
"We're coming up to a very severe situation where several infections in humans are no longer treatable. If we don't change some of our practices both in the clinic and agriculturally, we're going to find in a very short period of time, five to ten years, increasing levels of these infections in people. We're already finding the concept of community acquired resistant infections, people who have no contact with hospitals in decades, now have what's called methecillin resistant staphylococcus aureus, a very difficult to treat staph infection. How did they get it? They got it because the genes are out there."
Bennet has begun studying how far the genes he's found in Iowa streams are travelling.
He wants to know if they're moving into the Mississippi, even making their way down to the Gulf of Mexico.
It's like an invisible web , expanding at an unknown rate.
But unlike many environmental problems, this one may pose the greatest threat not to wildlife, but to people.
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