Since the late 1940s, so-called “subtherapeutic” doses of antibiotics have been routinely added to animal feed to prevent disease and to increase feed efficiency. Exactly why animals put on weight more readily when exposed to small doses of antibiotics isn’t clear, but it may have to do with reducing the competition for nutrients by cutting down on the natural bacterial population in the animals’ gut. Some studies also suggest that antibiotic use thins the intestinal wall and increases nutrient absorption. What has become clear, however, is that such subtherapeutic use of antibiotics leads to the flourishing of antibiotic resistant bacteria in animals and that such bacteria can infect humans. Chickens, for example, will begin to excrete antibiotic-resistant E. coli in their feces just 36 hours after being given tetracycline-laced feed. Within a short time these bacteria also show up in the feces of farmers. And a truly frightening prospect is that bacteria can pass genes between each other, including the ones that make them resistant to antibiotics. This means that bacteria that have never been exposed to an antibiotic can acquire resistance just by encountering resistant ones. Then consider that animals shed bacteria in their feces and that manure is used as fertilizer, and fertilizer gets into ground water, and it quickly becomes evident how the bacterial resistance problem can mushroom.
Thorough cooking of course kills bacteria, but the widespread incidence of food poisoning demonstrates that poor food handling and undercooking is common. True, most people who come down with bacterial food poisoning just experience some unpleasant cramps and diarrhea and recover without the need for antibiotic treatment. In this case resistance is not an issue. But there are numerous cases of children, the elderly, or people whose immune system is compromised, who need antibiotic treatment for food poisoning. And now if the bacteria are resistant to antibiotics, these patients can face a dire situation. Take for example the case of an unfortunate Danish woman who died in 1998 after eating Salmonella-infected pork. She failed to respond to ciprofloxacin (Cipro), the usual antibiotic of choice, because of bacterial resistance. In a piece of elegant research, Danish scientists succeeded in genetically matching the Salmonella-resistant strain to a specific pig farm. Surprisingly, these pigs had not been treated with ciprofloxacin, but the pigs on neighbouring farms had been, and the resistant bacteria had moved between farms!
In North America antibiotics known as quinolones have been used since 1995 to treat infections in poultry. While this was great for the chickens’ health, it turned out not to be so good for humans. The most common cause of bacterial gastroenteritis in people is Campylobacter jejuni, and poultry is often responsible. If an antibiotic is needed, ciprofloxacin is the usual choice. But since the introduction of quinolones to farm animals, Campylobacter strains resistant to the drug have emerged. The Food and Drug Administration in the U.S. has recognized this as such a serious problem that it has made Baytril, a quinolone, the first veterinary drug to be banned because of the emergence of resistant bacteria. While this is the first action of its kind in North America , Europeans have been phasing out antibiotics in animal feed since the 1980s. Sweden banned the use of antibiotics as growth promoters in 1986 and Swedish farmers responded by improving hygiene on farms and by altering feed composition. They showed that meat can be produced for the consumer at virtually the same cost as with antibiotics. And without a cost to consumers’ health! The European Union has followed suit and on January 1, 2006 banned the use of antibiotics as growth promoters in animal feed. That actually hasn’t resulted in a huge reduction in antibiotic use. While the prophylactic use has decreased, there has been an increase in the therapeutic use of antibiotics in animals because there has been an increase in illness that apparently was being prevented by antibiotics added to feed.
Antibiotics are wonderful drugs and we must do all we can to protect their efficacy. While certain uses of antibiotics to treat sick animals are justified, as one scientist who studies antibiotic resistance opined, “Cipro is an essential antibiotic, and we cannot allow its effectiveness to be compromised by squandering it on poultry.”