Leaking genes

Bacterial resistance to antibiotics increases
because we give bacteria too many opportunities.

Hog farm in Missouri

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.

While we scorn doctors that prescribe antibiotics unnecessarily, we’re also beginning to shop for meat and poultry products that are raised without routine antibiotic feed additives. And one day we will be brave enough to stop teaching bacteria by quitting the routine use of antiseptics in our household.

Many producers have quit the routine use of antibiotics for young birds and during weaning. But many farmers remain eager because protecting young livestock from bad bacteria increases growth.

But it’s difficult to keep antibiotics out of the environment. We know where the feed goes. Antibiotics accumulate in animal waste and into waste water from washing, into waste lagoons, drops along the ground and leaches into groundwater. Exposing bacteria to our arsenal of antibiotics increases the likelihood bacteria will develop resistance.

Not much leaks away
One study says not to worry; the volume of antibiotics reaching the soil and groundwater is minimal. Paul Sibley from the University of Guelph has shown that environmental contamination from antibiotics does not pose significant risks to soil and aquatic organisms.

Sibley’s six years of research examining the use of pharmaceuticals found the “toxicity effects of pharmaceuticals were in the milligram- to gram-per-litre range” and “wasn’t necessarily high enough to pose any danger.”

But do we measure the wrong threat?
We may be incorrectly measuring toxicity and resistance. The risk may not be in the amount of antibiotics we find downstream, but from the bacteria’s genes passed like a baton in soil and groundwater.

R.I. Mackie, a professor at the Institute for Genomic Biology, conducted one of the first surveys of the bacterial genes that directly pass tetracycline resistance from hog waste lagoons into groundwater wells. Wells that were closest to the lagoon “almost always had every gene.”

Accelerating bacterial resistance by increasing antibiotics in groundwater and the environment remains a serious risk. Mackie says:

“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.”

Tip to Doug Powell at Agnet