Is agriculture promoting antibiotic resistance?
Avoiding an increase in antibiotic resistance among bacteria -- which would lay us open to epidemics reminiscent of the Middle Ages -- is high on the list of organizations promoting the safe use of antibiotics.

For example, this from two scientists from the World Health Organization: "There is growing concern that the control of infectious diseases is threatened by the upward trend in the numbers of bacteria that are resistant to multiple antibiotics in the medical armamentarium" (see "Containment of Antibiotic Resistance" in the bibliography).

There is also growing evidence that feeding human antibiotics to farm animals causes antibiotic resistance in the animals, and that the bacteria can infect people. Writing in Science magazine in 1998, Wolfgang Witte, of the Robert Koch Institute in Germany, observed that "Fluoroquinolone use in poultry husbandry has promoted the evolution of fluoroquinolone-resistant Campylobacter jejuni, which has been detected in meat products and infected human patients." The fluoroquinolones include ciprofloxacin, a powerful, relatively new antibiotic that doctors use to kill bugs immune to older drugs (see "Quinolone-resistant..." in the bibliography).

A 1999 study related feeding quinolone antibiotics to poultry in Minnesota to human infections with antibiotic-resistant strains of the bacterium Campylobacter jejuni. The authors concluded that feeding the antibiotic to poultry -- a practice that began in 1995 -- had created a "reservoir" of antibiotic-resistant microbes that had infected people (see "Quinolone-resistant..." in the bibliography).

Doom say?
A key concern is that the development of bugs that laugh at vancomycin (a last line of defense against bacteria that resist all other antibiotics) could lead to a "doomsday scenario" with bacterial epidemics reminiscent of the Dark Ages. In 1997, the European Union banned avoparcin, a drug related to vancomycin, from animal feed after studies linked it to the development of vancomycin-resistant bacteria. In 1998, the European Union banned four more antibiotics for similar reasons.

As we've said, the exact amount of antibiotic resistance due to farm practices is controversial and unknown. Cook, who says "I think it's a real issue," adds that "overwhelmingly there have not been many good studies on the issue."

Some experts are less equivocal. For example, Timothy Paustian, faculty associate, department of bacteriology, University of Wisconsin-Madison, says "we should not be wasting the precious resources of antibiotics on getting our cattle fat faster. It's a stupid idea and will always be a stupid idea. These are life-saving drugs we use to fight off infection, and to be throwing them at cattle that are not going to die anyway is stupid." A 1994 workshop sponsored by the World Health Organization reiterated a 1969 report by an expert committee from the United Kingdom. That group, the Swann Committee, argued that to avoid antibiotic resistance, animals should not receive human antibiotics.

A slight edge
To evaluate the situation, we must also look at the benefits of using antibiotics as growth promoters. According to Witte, farm animals gain 4 percent to 5 percent more body weight with antibiotics. Cook says the cost of production would increase by $300 million for broiler chickens in the United States.

Against a total production cost of about $14 billion, we calculate that broiler industry costs would rise by slightly more than 2 percent if they lost the use antibiotics as promoters. But the withdrawal could have ripple effects, Cook adds. If drug manufacturers could no longer amortize development costs across animals and people, it's possible that drug costs would rise, or that fewer drugs would be developed.

Another uncertainty concerns the question of whether breeding practices have impaired farm animals' immune systems. "We have been genetically selecting animals, particularly poultry, for a lack of response to these bugs," says Cook. But because an active immune system cuts weight gain, breeding for size means breeding for decreased immunity. "In generation after generation, you select the biggest animals, and you are selecting for animals" that have less immune response," Cook says.

In other words, farm animals might be more susceptible to disease without antibiotics.

At any rate, with few promising new antibiotics in the pipeline, the benefits of preserving these life-saving drugs could outweigh the increased cost to farmers. The Why Files won't tell you what to think, but we did cover antibiotic resistance.

Got a bright idea for minimizing the routine feeding of antibiotics to farm animals?

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