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- Bacteria that have developed immunity
to antibiotic drugs pose a large and growing threat to the success of modern
medicine. Three studies now find that U.S. rivers have become a major reservoir
of such microbes.
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- Reported at the American Society for
Microbiology (ASM) meeting this week in Chicago, the studies demonstrate
that antibiotic resistance is literally streaming across the nation.
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- Ronald J. Ash of Washburn University
in Topeka, Kan., sampled waterborne bacteria from 15 U.S. rivers, including
the Mississippi, the Ohio, and the Colorado. He tested the microbes' resistance
to ampicillin, a synthetic penicillin.
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- At each of the 21 sites examined, ampicillin
failed to kill between 5 and 50 percent of the bacteria. Though most of
these bacteria are not types usually linked to disease, Ash notes that
any bacterium can transfer its drug-resistance genes to pathogenic organisms
in either the environment or a host.
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- Finding antibiotic-resistant bacteria
in rivers is hardly novel. "What has not been appreciated is the extent
of contamination," Ash says.
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- Because he found resistant bacteria both
near major cities and in remote areas, Ash says, "I can't say that
I see any patterns." In fact, he expected the water near New Orleans,
at the end of the Mississippi, to be loaded with resistant bacteria, but
they weren't particularly plentiful there.
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- Antibiotic resistance is widespread but
also unpredictable in the Rio Grande, finds Keith L. Sternes of Sul Ross
State University in Alpine, Texas. He focused on enterococcus bacteria
resistant to vancomycin. This drug is often a last line of defense against
potentially lethal infections, such as those caused by Staphylococcus aureus
bacteria that have become immune to the penicillin family of drugs (SN:
4/24/99, p. 268).
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- Sternes tested water from the Rio Grande
River's headwaters in Colorado down to Presidio, Texas, at intervals of
50 miles or less. Though resistance was most prevalent downstream of El
Paso"detected in up to 30 percent of the bacteria there"it was
not always highest adjacent to big cities or ranches.
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- John Bennett of Clarke College in Dubuque,
Iowa, found plenty of antibiotic-resistant bacteria"including pathogenic
Escherichia coli and Salmonella"while testing 95 percent of the permanent
streams in rural Dubuque County. He zeroed in on resistance to tetracycline,
a drug widely used for livestock and people.
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- In some waters, just 1 percent of the
bacteria proved immune to tetracycline. In others, 30 to 40 percent resisted
the drug. Moreover, Bennett found that greater than 80 percent of the tetracycline-resistant
bacteria examined were also immune to one to six additional antibiotics.
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- Tainted water probably explains the resistant
bacteria in wild Canada geese living year-round in Chicago's suburbs, says
Monica L. Tischler of Benedictine University in Lisle, Ill. From goose
feces, she isolated 179 types of bacteria, many of which showed strong
resistance to streptomycin, erythromycin, vancomycin, tetracycline, and
penicillin-family drugs. Resistance rates ranged from 2 to 100 percent,
depending on the microbe and antibiotic tested.
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- "The surprise was that we found
any resistance," says Tischler. With little human contact or direct
access to farms, these birds "should have had absolutely no exposure
to antibiotics, unless it's through their environment," she says.
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- "The most important source of environmental,
antibiotic-resistant bacteria is domestic animals," says Richard Novick
of New York University Medical Center. Farmers often feed livestock low
doses of antibiotics to boost growth (SN: 7/18/98, p. 39). Inevitably,
some bacteria in the animals, in manure-tainted fields, and in local waters
evolve to coexist with the drug. Such resistant bacteria also develop in
people taking antibiotics, he notes.
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- This resistance, which undermines the
effectiveness of drugs, "is a reflection of our heavy antibiotics
use," indeed overuse, says ASM President Stuart B. Levy of the Center
for Adaptation Genetics and Drug Resistance at Tufts University in Boston.
That the resistance has spilled over into wild animals, such as geese,
should "provoke a cry" to use antibiotics more judiciously, says
Levy.
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- References:
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- Ash, R.J., et al. 1999. Antibiotic-resistant
bacteria in U.S. rivers (Abstract Q-383). In Abstracts of the 99th General
Meeting of the American Society for Microbiology (May 30-June 3):607. Chicago.
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- Bennett, J., and G. Kramer. 1999. Multidrug
resistant strains of bacteria in the streams of Dubuque County, Iowa (Abstract
N-86). In Abstracts of the 99th General Meeting of the American Society
for Microbiology (May 30-June 3):464. Chicago.
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- Eichorst, S. . . . M.L. Tischler. 1999.
Antibiotic resistance among bacteria isolated from wild populations of
resident Canada geese in a suburban setting (Abstract Q-402). In Abstracts
of the 99th General Meeting of the American Society for Microbiology (May
30-June 3): Chicago.
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- Sternes, K.L. 1999. Presence of high-level
vancomycin resistant enterococci in the upper Rio Grande (Astract Q-63).
In Abstracts of the 99th General Meeting of the American Society for
Microbiology (May 30-June 3):545. Chicago.
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