Sludge Watch ==> Tracking Antibiotic Resistance from Swine Farms to Groundwater

[Maureen Reilly]

Sludgewatch Admin:
The same lessons need to be learned from sewage sludge and antibiotic 
resistance.
Only this time it is human antibiotics that the bacteria are resistant to.

Veterinarians use only some ranges of antibiotics reserving some for 
exclusive human use, in an effort to have some drugs that will continue to 
work even when patients have acquired antibiotic resistant strains of 
disease.

However, many hospitals now routinely dose surgery patients pre-operatively 
with these reserved broad spectrum antibiotics...thus flushing those 
antibiotics to the sewer system where bacterial pathogens in the digesters 
and sludge lagoons can develop resistance.

Then we land apply them where we grow our food.

Scary.

..............................................


Public release date: 21-Aug-2007


Contact: Diana Yates
diya at uiuc.edu
217-333-5802
University of Illinois at Urbana-Champaign

Team tracks antibiotic resistance from swine farms to groundwater

The routine use of antibiotics in swine production can have unintended 
consequences, with antibiotic resistance genes sometimes leaking from waste 
lagoons into groundwater.

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.

Editor’s note: To reach Tony Yannarell, call 217-333-8809; e-mail: 
acyann at uiuc.edu. To reach R.I. Mackie, email: r-mackie at uiuc.edu.

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http://www.eurekalert.org/pub_releases/2007-08/uoia-tta082107.php