[Pharmwaste] Team Tracks Antibiotic Resistance From Swine Farms To
dldebiasi at deq.virginia.gov
Wed Aug 22 09:47:57 EDT 2007
Source: University of Illinois at Urbana-Champaign
Date: August 22, 2007
Team Tracks Antibiotic Resistance From Swine Farms To Groundwater
Science Daily - The routine use of antibiotics in swine production can
have unintended consequences, with antibiotic resistance genes sometimes
leaking from waste lagoons into groundwater.
A research team tracked the movement of tetracycline resistance genes
from wastewater lagoons to groundwater at two Illinois hog farms. Red
circles mark the locations of groundwater testing wells on Site A, the
more impacted facility. The lagoon is unlined. (Credit: Photo couttesy
In a new study, researchers at the University of Illinois report that
some genes found in hog waste lagoons are transferred - "like batons" -
from one bacterial species to another. The researchers found that this
migration across species and into new environments sometimes dilutes -
and sometimes amplifies - genes conferring antibiotic resistance.
The new report, in the August issue of Applied and Environmental
Microbiology, tracks the passage of tetracycline resistance genes from
hog waste lagoons into groundwater wells at two Illinois swine
This is the first study to take a broad sample of tetracycline
resistance genes in a landscape dominated by hog farming, said principal
investigator R.I. Mackie. And it is one of the first to survey the genes
directly rather than focusing on the organisms that host them. Mackie is
a professor in the department of animal sciences and an affiliate of the
Institute for Genomic Biology.
"At this stage, we're not really concerned about who's got these genes,"
Mackie said. "If the genes are there, potentially they can get into the
right organism at the right time and confer resistance to an antibiotic
that's being used to treat disease."
Tetracycline is widely used in swine production. It is injected into the
animals to treat or prevent disease, and is often used as an additive in
hog feed to boost the animals' growth. Its near-continuous use in some
hog farms promotes the evolution of tetracycline-resistant strains in
the animals' digestive tracts and manure.
The migration of antibiotic resistance from animal feeding operations
into groundwater has broad implications for human and ecological health.
There are roughly 238,000 animal feeding operations in the U.S., which
collectively generate about 500 million tons of manure per year.
Groundwater comprises about 40 percent of the public water supply, and
more than 97 percent of the drinking water used in rural areas.
Federal law mandates that animal facilities develop nutrient management
plans to protect surface water and groundwater from fecal contamination.
Most swine facilities hold the effluent in large, water-filled lagoons
until it can be injected into the ground as fertilizer. Thanks to a
change in the law in the late 1990s, new lagoons must be built with
liners to prevent seepage. Swine facilities in operation prior to the
new regulations are allowed to continue using unlined lagoons, however.
Some of these lagoons leak.
The researchers extracted bacterial DNA from lagoons and groundwater
wells at two study sites over a period of three years. They screened
these samples for seven different tetracycline resistance genes.
They found fluctuating levels of every one of the seven genes for which
they screened in the lagoons. They also found that these genes were
migrating from the lagoons to some of the groundwater wells.
It should be noted that many genes that confer antibiotic resistance
occur naturally in the environment. Tetracycline is itself a bacterial
product, employed by Streptomyces bacteria long before humans discovered
In order to determine the origin of the tetracycline resistance genes
found in the groundwater, the researchers conducted a genetic analysis
of one gene family, tet(W), in samples from the lagoons and from
groundwater wells below (downgradient of) and above (upgradient to) the
lagoons. They found that the variants of tet(W) genes in the upgradient,
environmental control wells were distinct from those of the lagoons,
while the wells downgradient of the lagoons contained genes consistent
with both the background levels and those in the lagoons.
"There's a human impact on these sites that is superimposed on a natural
signal," said postdoctoral research assistant Anthony Yannarell, an
author on the study.
One of the two hog farms, "Site A," was more impacted by resistance
genes from the lagoon, due to its hydrogeology. The site included two
layers of sand - at about two meters and eight meters below the surface
- through which groundwater flowed.
"Every time we looked in the lagoon, we saw all of the genes we were
looking for," Yannarell said. "At Site A, all the wells that were
closest to the lagoon almost always had every gene. As you got further
from the lagoon you started to see genes dropping out."
The resistance genes were present at much higher levels - "an order of
magnitude higher," said the authors - in the lagoon than in the
contaminated wells. Most were diluted as they moved away from the
lagoons in the groundwater.
There was one notable exception. A gene known as tet(C) was found at
higher levels in some of the groundwater wells at Site A than in the
lagoon. Its heightened presence was not consistent with background
levels, indicating that something in the environment was amplifying this
one gene, which had originated in the lagoon.
Perhaps the gene had migrated to a new organism, Yannarell said, to find
a host that was more suited to conditions in the groundwater.
"What we are seeing is that the genes can travel a lot further than the
bacteria," Mackie said. "It's a matter of getting the DNA into the right
organism. It's a relay race."
Other authors on the study are postdoctoral research assistant S. Koike;
Illinois State Geological Survey geochemist I.G. Krapac; research
assistant H.D. Oliver; USDA Agricultural Research Service scientist and
professor of crop sciences J.C. Chee-Sanford; and visiting professor of
animal sciences R.I. Aminov.
Note: This story has been adapted from a news release issued by
University of Illinois at Urbana-Champaign.
Deborah L. DeBiasi
Email: dldebiasi at deq.virginia.gov
WEB site address: www.deq.virginia.gov
Virginia Department of Environmental Quality
Office of Water Permit Programs
Industrial Pretreatment/Toxics Management Program
Mail: P.O. Box 1105, Richmond, VA 23218 (NEW!)
Location: 629 E. Main Street, Richmond, VA 23219
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