Big Agriculture creating new
generation of antibiotic-resistant super bugs
group of Canadian and French scientists have uncovered more
evidence that prolific use of antibiotics in animal
agriculture is contributing to the development of
drug-resistant "super-bugs," in a study published in Journal
of Environmental Quality and funded by Agriculture and Agri-Food
Feeding antibiotics to
healthy animals is a common practice in industrial
agriculture, because it is believed to reduce rates of
illness and to result in larger animals and therefore,
But many health advocates
have raised concerns that this practice may accelerate the
evolution of antibiotic-resistant bacteria.
These bacteria might evolve directly in the animals' bodies,
becoming super-bugs if they somehow spread to humans (as in
E. coli contamination from cattle feces).
In addition, large quantities of unmetabolized antibiotics
are secreted in farm animals' manure, which is then used as
fertilizer all across North America - creating the potential
for the evolution of drug resistance in the wider
In the new study, researchers found a new, previously
unknown type of drug resistance that combined two already
well known bacterial abilities.
It is well established that
bacteria readily evolve two major forms of drug-resistance:
either they develop ways to purge drugs from their cells, or
they metabolize the drugs to make them less harmful.
Likewise, it is well known
that some bacterial species can actually consume certain
pesticides for food - to such an extent that those chemicals
become ineffective in fields where such bacteria reside.
Now, researchers have found a species of bacteria that eats
antibiotics for food.
"I think it's kind of a game changer in terms of how we
think about our environment and antibiotic resistance," Topp
Producing new super-bugs
14 years ago, Topp and colleagues began a long-term study in
which they gave soils an annual treatment with three
different veterinary antibiotics: sulfamethazine, tylosin,
They wanted to find out
whether over time, this would encourage the evolution of
antibiotic resistance in soil bacteria.
A few years ago, the researchers decided to start another
concurrent study comparing the rate at which antibiotics
broke down in soil that had received repeated doses versus
soil that had never been dosed before.
This was based on prior
findings that many pesticides break down more quickly in
soil where they have been regularly applied. The researchers
wanted to find out if there was any selection for
antibiotic-degrading microbes, which had never before been
To their shock, they found that sulfamethazine broke down
five times faster in soil that had been regularly exposed to
it. They eventually determined that a strain of
Microbacterium - from a family called actinomycete that are
known to break down many organic compounds - was actually
using sulfamethazine as food. Since then, two other strains
of Microbacterium have been found to break down antibiotics
in the sulfanomide family.
This implies that continued use of agricultural antibiotics
may be exerting a pressure on soil bacteria to evolve
antibiotic-digesting abilities, Topp noted. This is an issue
of particular concern because unrelated bacterial species
are able to swap genetic material.