Antibiotic Resistance Moving to Groundwater

Antibiotic Resistance Moving to Groundwater



 
Aug. 2007  - The routine use of 
antibiotics in swine production can have unintended consequences, with 
antibiotic resistance genes sometimes leaking from waste lagoons into 
groundwater, according to new research from the University of Illinois. 
Researchers report that some genes found in hog waste lagoons are 
transferred, "like batons," from one bacterial species to another. This 
migration across species and into new environments sometimes dilutes, and 
sometimes amplifies, genes conferring antibiotic resistance, they say. 
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. 

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. 
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, a professor in the University of Illinois-Champaign 
department of animal sciences and an affiliate of the Institute for 
Genomic Biology. 
It is one of the first studies to survey the genes directly rather than 
focusing on the organisms that host them, he says. 
"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." 
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, and they found that these genes were 
migrating from the lagoons to some of the groundwater wells. 
"Every time we looked in the lagoon, we saw all of the genes we were 
looking for," said postdoctoral research assistant Anthony Yannarell, an 
author on the study. "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." 
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. 
Due to a change in the law in the late 1990s, new lagoons must be built 
with liners to prevent seepage, but swine facilities in operation prior to 
the new regulations are allowed to continue using unlined lagoons, and 
some of them leak. 
The migration of antibiotic resistance from animal feeding operations into 
groundwater has broad implications for human and ecological health. 
There are about 238,000 animal feeding operations in the United States, 
which collectively generate about 500 million tons of manure per year. 
Groundwater make up about 40 percent of the public water supply, and more 
than 97 percent of the drinking water used in rural areas. 

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