Antibiotics in Agriculture

December 28, 2010

I’ve written several times before (here, for example) about the problem of bacteria resistant to antibiotics.  From a present-day perspective, it is hard to realize that infections, before the advent of antibiotics, were a very serious health threat, and not infrequently fatal.  So the possibility of running out of effective antibiotic therapies is something to take seriously.

It is obvious that any use of antibiotics creates evolutionary selection pressure favoring resistant organisms,  (Sir Alexander Fleming, discoverer of penicillin, saw evidence of developed resistance in his work.)   The use of antibiotics to treat infections in people has clearly been a huge positive for human health.  We don’t want to lose that; we do want to discourage doctors prescribing antibiotics indiscriminately (or just to make the patient feel that something is being done), and we want to encourage people to finish any course of antibiotics that is prescribed.

There are other potential sources of antibiotic resistance, though.  There is evidence that some other commonly used chemicals (such as triclosan) may also create selection pressure for antibiotic resistance; and large quantities of antibiotics are used in agriculture, not just to treat sick animals, but as a regular addition to food or water, in order to promote faster growth.  The food industry has always dismissed the idea that this could be a meaningful source of antibiotic resistance in humans; it has been difficult to get information on the quantities of antibiotics actually used.

A recent article at Wired provides some fresh evidence, based on data from a post at the Center for a Livable Future [CLF] blog.   (The blog is written by staff at the Center for a Livable Future at Johns Hopkins Bloomberg School of Public Health; posts on the blog are personal views, not official positions of the School.)   The FDA recently released information on the total amount of various antibiotics sold in the US for veterinary or agricultural purposes.  The CLF researchers have managed to come up with figures for the total amount of antibiotics used in humans, from a separate study.  The combined results show that 80% of the antibiotics used in the US are used on farm animals.   For example, about 10.2 million pounds of tetracycline antibiotics are given to animals each year, more than the amount of all antibiotics given to people.

The food industry, of course, denies that this is a problem, partially on the basis that some of the antibiotics that they use are not exactly the same as the ones used in human medicine (many of them are identical).  This is really a red herring; as the CLF authors wrote:

LivableFutureBlog readers might recall an October blog post in which Dr. Ellen Silbergeld, professor of environmental health sciences at the Johns Hopkins Bloomberg School of Public Health, warned that, “Bacteria respond to chemical structures, not brand names, and resistance to one member of a pharmaceutical class results in cross resistance to all other members of the same class.”

I have not heard anyone object to the therapeutic use of antibiotics for animals that are actually sick; the issue is the routine addition of antibiotics to the animals’ diets to promote faster (= cheaper) growth.   Since this practice is of economic value to the producers, they are virtually certain to resist any attempt to curtail it, but  the scientific evidence suggests that to continue with business as usual would be almost breathtakingly stupid.


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