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Jane Brody
Three studies to be published today in The New England Journal of
Medicine provide new evidence of a problem that physicians and
scientists have been warning about for decades: the routine use of
antibiotics to enhance growth in farm animals can encourage the growth
of drug-resistant bacteria, which may threaten people who undercook
their meat or consume food or water contaminated by animal droppings.
Furthermore, because genes that confer resistance to drugs can jump from
one organism to another, the studies suggest that resistance can spread
to many types of infections.
The problem goes beyond food poisoning. An antibiotic-resistant strain
of the common intestinal bacterium E. coli was recently found to cause
many urinary tract infections that resisted treatment. Researchers
suspect that people may have picked up the resistant strain from food.
The overuse of antibiotics in human medicine has also contributed to the
emergence of antibiotic resistance, experts say. That concern is one
reason that doctors are urging people worried about anthrax not to take
Cipro, an antibiotic effective against the disease, unless they have
reason to believe they have been exposed to the spores that cause it.
Cipro belongs to an important class of powerful antibiotics,
fluoroquinolones, and if they stop working, many infections could become
difficult or impossible to treat, scientists say.
The new findings mirror the results of many earlier studies. Dr.
Sherwood L. Gorbach, an infectious disease specialist at Tufts
University's medical school who wrote an editorial accompanying the new
reports, urged a ban on the routine use of low-dose antibiotics to aid
animal growth and prevent infection, as it sets up ideal conditions for
the emergence of resistant bacteria.
This year, the Union of Concerned Scientists, a nonprofit group based in
Cambridge, Mass., estimated that 26.6 million pounds of antibiotics are
administered to animals each year, with only 2 million pounds used to
treat active infections; the rest is used to prevent infection or
promote growth. Three million pounds of antibiotics are used in people
each year.
The Food and Drug Administration has tried for years to tighten controls
over the use of antibiotics in farm animals, a practice the European
Union banned in 1998. Dr. Gorbach recommended that antibiotics for farm
animals be prescribed by veterinarians only to treat infections, and
that certain antibiotics critically important in human medicine never be
given to animals.
But Ron Phillips, a spokesman for the Animal Health Institute, a trade
group representing manufacturers of veterinary drugs, said: "The way to
manage antibiotic resistance is not by banning products but by judicious
use and robust surveillance that gives an information base on which to
make informed management decisions. Antibiotics are used to raise
healthy animals. They're vitally important to delivering a safe,
wholesome supply of meat to the American consumer."
In one of the new studies, directed by Dr. Frederick J. Angulo, a
veterinarian at the federal Centers for Disease Control and Prevention,
researchers examined 407 samples of chicken from 26 supermarkets in four
states: Georgia, Maryland, Minnesota and Oregon. The researchers found
that 237 of the chicken samples were contaminated with the bacterium
Enterococcus faecium, which was resistant to a potent combination of
antibiotics.
The same bacteria were also found in 3 of 334 stool samples from people
being treated as outpatients. The antibiotics that the bacteria
resisted, quinupristin and dalfopristin, used in combination, are
critically important in treating E. faecium infections that are
resistant to vancomycin, the usual treatment for this organism.
A second study, by scientists at the University of Maryland and the
F.D.A., examined 200 samples of ground meats -- chicken, beef, turkey
and pork -- from three supermarkets in the Washington, D.C., area. A
fifth of the samples were contaminated by salmonella, a leading cause of
food poisoning. Antibiotic resistance was rampant among the contaminated
samples, with 84 percent resistant to at least one antibiotic and 53
percent resistant to at least three antibiotics. And some of the
salmonella bacteria, including one especially virulent strain, had
become "superbugs," resisting 9 to 12 antibiotics.
Although most salmonella infections get better on their own within a
week, in up to 10 percent of cases the infection invades the
bloodstream, where it can be deadly.
The director of the second study, Dr. Jianghong Meng, of the University
of Maryland, said that, while new practices in the food industry are
helping to control harmful organisms, the agricultural sector "is not
doing a very good job of controlling the emergence of resistant
organisms."
The third study was conducted at Statens Serum Institut in Copenhagen,
with 18 healthy volunteers. It was designed to test how well
antibiotic-resistant bacteria from meat survive in the human digestive
tract.
Twelve volunteers ingested antibiotic-resistant organisms from chicken
or pork, and six ate antibiotic-susceptible strains from chicken.
Afterward, the same strains were isolated from the volunteers' stools
for up to 14 days, indicating that both the antibiotic-resistant and
antibiotic-susceptible bacteria survived the trip through the digestive
tract and were able to multiply there. |
