Subject: Fw: Antibiotic Resistance from Swine to Groundwater

 

 


 



Source:

University <http://www.uiuc.edu/>  of Illinois at Urbana-Champaign


Date:

August 22, 2007

More on:

Water <http://www.sciencedaily.com/news/earth_climate/water/> , Agriculture
<http://www.sciencedaily.com/news/plants_animals/agriculture_and_food/>  and
Food, Recycling
<http://www.sciencedaily.com/news/earth_climate/recycling_and_waste/>  and
Waste, Bacteria <http://www.sciencedaily.com/news/plants_animals/bacteria/>
, Developmental
<http://www.sciencedaily.com/news/plants_animals/developmental_biology/>
Biology, Evolutionary
<http://www.sciencedaily.com/news/plants_animals/evolution/>  Biology


Team Tracks Antibiotic Resistance From Swine Farms To Groundwater


 <http://www.sciencedaily.com/> 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 R.I. Mackie) 


 

 

  _____  

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 facilities. 

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 its
usefulness. 

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.


 

 

 

 


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