Many health experts have raised concerns that the use of antibiotics in the
meat and poultry industry -- whether to promote growth or prevent illness -- may
contribute to the emergence of new drug-resistant bacteria. The fear is that
there will then be fewer treatment options for the people and animals who get sick
from these superbugs. Here, epidemiologist Glenn Morris, journalist Michael Pollan,
and feedlot operator Bill Haw discuss the antibiotic controversy with
Professor and chairman of the department of epidemiology and preventive medicine at the University of Maryland Medical School
Can you explain the controversy around feeding antibiotics to the animals we
For example, if you treat chickens with bacteria with antibiotics over a long
enough period of time, the bacteria will develop resistance. What you run into
are problems with resistant microorganisms that may then colonize the chickens.
What tends to happen in a chicken house is that when you get one flock that
you've treated with antibiotics and maybe developed a few resistant organisms,
those resistant organisms are in the fecal material that gets down into the
litter. When you introduce a new flock, it's going to pick at the litter and
pick up those resistant organisms, and so potentially one dose of antibiotics
may result in successive generations of chickens coming through that chicken
house carrying a resistant microorganism.
What's wrong with that?
The problem is, if a resistant microorganism is something like salmonella or
campylobacter, when we humans contract the illness from eating chicken that's
not properly cooked or from a variety of other reasons, we may not respond to
antibiotic treatment. One of the things that's worried us most recently has
been the increase in the percentage of campylobacter isolates that are
susceptible to Ciprofloxacin, which is the drug we use or have used in the past
for treating campylobacter of gastroenteritis. Even if a chicken's carrying campylobacter, if you handle the chicken properly and use appropriate techniques, you won't acquire it. But if there is a
breakdown somewhere in the system and you do end up consuming some
campylobacter and get sick, there's basically about a 20 percent chance that
the campylobacter that you have just consumed is not going to be killed by
Ciprofloxacin. That's a problem. This is in comparison, say, to the early 1990s,
when probably only 1-3 percent of campylobacter were resistant to
something like Ciprofloxacin.
Microorganisms tend to develop resistance to Ciprofloxacin fairly easily. We
become concerned about our ability to use Ciprofloxacin as a means of treating
campylobacter infections because of the rapidly increasing rates of resistance.
[We are concerned that] because of the large amounts of antibiotics we're
using, we are developing increasingly resistant microorganisms and we are
reducing our ability as physicians to treat patients who come into us with
infections. No longer can you assume that whatever the person is infected with
you can treat it. Frequently we're beginning to encounter these microorganisms
that in some cases are not susceptible to the first line or second line or even
third line treatment. There are strains of salmonella which are resistant to a
large number of antibiotics. And while they are still potentially treatable,
most of our standard drugs will not work against some of these strains. Our
concern is that the use of antibiotics in an agricultural setting is one of the
things that's contributing to the emergence of these strains.
And, of course, Ciprofloxacin is used for a variety of other settings. It's the
drug that is now one of the primary drugs for treatment of anthrax. ... These
days Ciprofloxacin is on everybody's mind. It's a potentially very valuable drug,
and to see development of resistance to Ciprofloxacin is always troubling.
How clear is the link between the resistance in animals and the resistance
In certain instances it's pretty clear, particularly if you're dealing with
pathogens such as salmonella or campylobacter, which are not really passed from
human to human. In most instances, they come through food. So when you see
increasing problems with resistance in microorganisms that really originate
primarily in food, it makes you look back at the food. In turn, it makes you
look back at microorganisms that are present in the animals.
So, we're challenging our ability to use antibiotics by the overuse of
antibiotics in our food supply.
Right. We're using a pretty good bit of antibiotic in our food supply for
growth promotion, as well as for therapy. Essentially, what that's doing is
developing generations of bacteria which now find it advantageous to carry
around resistance genes. And those increasingly resistant bacteria are in turn
moving into human populations. There's sort of this tendency to think, "Well,
that's agriculture, this is humans," but we really are all together. It's a
single ecosystem and we have to be concerned about what's happening in
agriculture in terms of the development of resistance.
Can you explain the notion of "sub-therapeutic" antibiotics?
When antibiotics were first identified, the observation was made that if you
fed animals low levels of antibiotics, lower levels than would be used to treat
an infection, for some reason they grew a little bit better, put on a little
bit more weight, and that little bit better growth can be the difference
between profit and loss in a really tight, low-profit margin operation. And
so, consequently, what has happened is that it has become almost standard
practice in our factory farming agriculture here in the United States to use
antibiotics as growth promoters.
The problem is that if you were to design a methodology for selecting out for
antibiotic resistance, this would be the way you'd do it. In the laboratory,
when we want to select out for resistance, what we tend to do is to treat
bacteria with levels of antibiotics that are not enough to kill them, but
enough to make them want to pick up or develop resistance genes. Consequently,
you've got a setting in which you are actually encouraging the development of
resistance. There's the feeling that to be able to make it economically, you
have to use the antibiotics, to be able to get away with the tight crowding and
all the other things that are used in agriculture, you need a little bit of
The tradeoff is that what you do is increase the risk that you're going to
develop resistant microorganisms, which are going to develop and select out
resistance genes, which in turn can reduce our ability to use antibiotics to
treat infections in humans as well as in animals.
Do we know how much antibiotics are fed to the animals we eat?
Antibiotics used in animal feeds are not something that there are good records
on. You can go to a feed store and buy a sack of feed with antibiotics without
a prescription. The drug companies have not provided good data on how much
antibiotic is being used. This is a major area of controversy between some of
the environmental groups and some of the producer groups. There's actually a
several-fold difference between what environment groups think may actually be
being used and what industry groups say is being used. It's fascinating that in
regard to something that should be simple there simply is no good data out
there. There's no federal regulation that really allows us to know how much
antibiotic is being used in agriculture. And the drug companies are not going
out of their way to make that data readily available. So we really don't know
how much antibiotic is being used in agriculture in this country. And that's
kind of scary.
His New York Times Magazine article "Power Steer" (March 31, 2002) traces the life of a cow destined for slaughter
Why are we using so much antibiotics? ... And are we using a lot of
Well, nobody knows exactly how many antibiotics we're using in agriculture,
because the industry is very tight lipped about it. But the Union of Concerned
Scientists did a study last year, and they found it was well over half the
antibiotics used do go to animals, for many reasons. Some of them are to treat
animals, which no one really has a problem with. Some of them, though, are for
what's called growth promotion. In many animals -- and this is particularly
true in chickens and pigs, for reasons we don't even understand -- if you give
low levels of antibiotics to an animal, it will grow more quickly. It may be
that it kills off low-level disease that was harming its productivity or
something like that. No one really understands why.
But in many cases -- and this is definitely true in beef -- we give them
antibiotics to keep them from getting sick from other things we're doing to
them. ... So a lot of it is prophylactic, is being used to prevent them from
getting sick. Then you also have the antibiotics used to keep them from having
liver disease because they can't digest the corn.
And so there were many, many reasons that we were using them. Very few of them
have to do with treating sick animals, although the beef case kind of confounds
the usual argument. If you talk to public health advocates, they say, "It's
fine to use antibiotics on sick animals; we just don't want them used for
growth promotion." But exactly how do you categorize an antibiotic you've
giving an animal because you've made it sick? And that's what we're doing. So
that kind of falls in the middle.
Why is this a problem? We exist in the same microbial environment as these
animals. So whatever you do to that ecosystem of germs, to them, is going to
rebound to us. ... Evolution is going on, and microbes are evolving to
withstand those antibiotics. This is how evolution works. When there is a
threat to the survival of any population, whatever members of that population ... are not susceptible, they then grow. Their population explodes. You select for resistance.
And that's what's happening. We're selecting for resistance in the guts of
these animals, in the manure on the ground, in the water downstream of these
places. And microbes are evolving that can withstand Cipro, that can
withstand Tetracycline, that can withstand [other antibiotics].
This is helping in hospitals, too. I mean, this is not the only cause of
antibiotic resistance. But given that most of the antibiotics are used in
agriculture, the belief is that a lot of these superbugs that are showing up in
hospitals that are not susceptible to any antibiotics are being created by
their process. ... And so you have this phenomenon [that] we simply can't
treat. We're getting antibiotic-resistant gonorrhea. We're getting
antibiotic-resistant tuberculosis. Public health advocates think perhaps this is the most serious threat to our public health over the next several years, because new antibiotics are
not coming along as fast as we thought they would. ...
One of the things we hear is that the industry is reducing its amounts of
antibiotics. ... Is it?
That's what they say. The chicken industry claims that they have reduced their
use of antibiotics, which is great, if true. It's on their own say-so. ... So
there is an effort to do it. ...For many, many years, agribusiness claimed that there was no public health
problem with their use of antibiotics. But the proof had not been found; the
link between human health and using antibiotics in agriculture had not been
established. Nobody makes that argument any more, except some real die-hard
spokesmen for the industry. The FDA, the CDC, every public health expert in the
country will tell you that there is a link between human health and the use of
antibiotics in agriculture.
As a result, the industry, I think in an effort to forestall regulations which
are on their way, has taken voluntary steps. The chicken industry, they say,
has reduced their use substantially, several companies. If true, it's terrific.
And it needs to be done. Whether they can do it without changing their
practices is an interesting question. Have they changed anything else? And if
they can reduce antibiotic use without having epidemics of disease on their
chicken farms or such loss of productivity, then why would they do it in the
So there are still a lot of questions about it. But we're definitely moving in
the right direction on that issue. ...
[How does the current system make antibiotic resistance] a bigger problem?
You have the system that could not survive without antibiotics. You could not
crowd animals into these feedlots or feed them this highly concentrated ration
without giving them antibiotics. But the antibiotics, in turn, lead to
resistance; resistant microbes that then come and infect us. So they're hidden
costs.If you follow the lines, ecology teaches you to see how things are connected.
And there was a direct result between feeding the animals corn, and then
antibiotics, and then us developing infections that we can't treat. ...
Everything is connected. ...
CEO of Kansas City's National Farms, which operates one of the
largest cattle feedlot operations in the country
Recently in the news, we've heard about the enormous use of antibiotics
within these confined feeding operations and the potential problems of that.
First of all, why are antibiotics used in a feedlot?
Antibiotics have been used historically in a variety of ways in feedlots. And I
think the way that has become controversial and is virtually eliminated now
from the industry is that certain antibiotics at very low levels tend to be a
growth promotant for the animal. That phenomenon was sort of accidentally
discovered, I think, and used at low-grade, feed-grade levels to promote growth
in the animals.
The concern is that low-levels of antibiotics will, by some theories -- and I
think there's certainly some logic behind it -- cause bacteria to become immune
to those antibiotics -- and that might be passed on to humans by consuming the
beef. I don't think there's any scientific evidence to corroborate that, but
it's not an illogical theory. So the feed-grade use of antibiotics has been
radically curtailed over the last number of years.
The other use of antibiotics is to treat specific illnesses in the animal. I
don't think there's much controversy on that. ...
But you don't believe that the low sub-therapeutic antibiotic feeding to
increase weight is problematic, in terms of developing antibiotic
On the contrary. I believe that's a legitimate theory. It's a theory that has
not been proven. But I think there's enough danger that it could be [and] that
we should be very, very careful in using sub-therapeutic level of
So why is so much of it still used? I understand that nearly half of the
antibiotics produced in this country are used for animal feed.
I think maybe the percentage of antibiotics that are used in animals is not
necessarily in animal feed, but to a much greater extent is being used in
specific treatment of specific illnesses in animals -- which, again, I don't
think is a controversial issue at all. So it's very easy to confuse the
sub-therapeutic use with the actual specific use for an animal who is sick. ...
Do you think that there isn't enough evidence that antibiotic use develops
First of all, I believe that the sub-therapeutic use of antibiotics does in
fact improve the rate of growth. The question in everybody's mind -- and in my
mind, too -- is whether or not the possible consequences of sub-therapeutic use
of antibiotics are worth taking the risk. And the risk, of course, is the
possibility that bacteria strains will become immune to those antibiotics. ... I
don't think there is any hard evidence that that immunity is transferred to
humans. But the possibility of it is an awesome thing.
How much are antibiotics used in feedlots today for weight gain?
I think you'd find that the use for weight gain had dramatically been reduced.
... I don't think it's been eliminated. But I think the use of sub-therapeutic
antibiotics is continuing to be restricted. And I think we'll find that more
and more -- certainly in our company -- the use of antibiotics indiscriminately
for any reasons has been virtually eliminated.
How can we show that? Because actually even getting the figures to how much
of the antibiotics are used in the feed has been extremely difficult. There are
no good numbers on it.
I'm not sure I know the answer to that. I know what my experience is. I know
what our company's experience is. And I know what my conversations with others
in the industry would indicate. There's a real concern that we want to act
responsibly. We should act responsibly. And I think the industry is very
quickly coming to that realization. ...
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