The federal government and the commercial farming industry are beginning to take action to protect the effectiveness of antibiotics in people by restricting their use in farm animals.
At the end of July, the Food and Drug Administration told the poultry industry to stop using the antibiotic Baytril, which is effective against many different germs, fearing that its continued use would weaken the use of similar antibiotics in people.
And earlier this month, pig-farming giant Smithfield Foods announced it would reduce the number of antibiotics it feeds its animals. McDonald's, and several other restaurant chains, already prefer to buy meat raised with reduced levels of antibiotics. Federal legislation is pending to help wean farmers off the use of the drugs.
Farmers have fed antibiotics to poultry, cows, and pigs for 50 years, to help them grow and prevent them from getting sick -- antibiotics that are similar to ones given to people to fight ear infections, strep throat, and other infections. Doctors are warned not to overprescribe such medications because the more people are exposed to them, the more likely it is that bacteria will become resistant. Then, when people really need the drugs, they won't work.
Although environmentalists have been concerned about antibiotics in farming for decades, the industry always insisted the drugs are safe.
Now, a growing body of scientific research is suggesting they may not be.
Although it is difficult to quantify the impact on the public, studies have shown that antibiotic-resistant bacteria from farm animals are present in the neighborhood grocery store, and can reach and survive in the human intestines. There is also some evidence that exposure to bacteria can make people sick: In one case, a 12-year-old boy's hard-to-treat salmonella poisoning was traced to a disease outbreak in cattle.
The fear is that an older person, who has spent a lifetime eating meat, will get the kind of food poisoning that would leave most people with an uncomfortable few days in the bathroom. But because the older person has a weaker immune system, the stomach ailment will land them in the hospital. Then, when the hospital tries to treat the illness with antibiotics, the drugs may fail.
''There are numerous examples of where antibiotic usage in the animal industry impacts what happens in humans," said Gary V. Doern, a clinical microbiologist at the University of Iowa.
But there still isn't enough evidence that food is linked to antibiotic resistance, according to some experts and industry officials.
''While it is clear that there is a potential for resistant bacteria to transfer between animals and humans, the question isn't 'can it' but 'does it'?" said Ron Phillips, vice president of legislative and public affairs at the Animal Health Institute, a trade organization representing manufacturers of animal health care products.
Charles Nightingale, co-director of the Center for Antimicrobial Research and Development at Hartford Hospital, said current research can't answer that question.
''You can't make any conclusions because there isn't enough data available," he said.
The industry doesn't provide information about how many antibiotics are fed to animals, but the Union of Concerned Scientists, an independent nonprofit advocacy group, estimates that 26 million pounds of antibiotics were fed to cattle, swine, and poultry in 2001 -- compared with 3 million pounds given to people that same year. Although people only take antibiotics when they are sick, animals are given these medications throughout their lives to promote growth and prevent disease.
Eating organic meat may help people avoid antibiotic resistance, according to a study presented at the American Veterinary Medical Association last month. Researchers at Ohio State and Iowa State universities found that turkeys raised without antibiotics, carried far less antibiotic-resistant bacteria than animals raised on conventional farms.
''It turns out that the organic meats are just as contaminated with bacteria -- but they are not drug resistant compared to conventionally farmed animals," said Linda K. Tollefson, deputy director at the FDA's Center for Veterinary Medicine, who attended the veterinary association meeting.
Antibiotic-resistant organisms are so common in conventional meats, research suggests, that they are present at the local supermarket. In 2001, a research team led by David White at the Food and Drug Administration analyzed the bacterial content of chicken, beef, turkey, and pork purchased from three supermarkets in the Washington, D.C., area. They found that 20 percent of these meats contained salmonella and more than half of the isolated bacteria were resistant to at least three antibiotics.
Stuart Levy, director of the Center for Adaptation Genetics and Drug Resistance at Tufts School of Medicine, is convinced that antibiotic resistant bacteria are making the leap from animals to people.
In 1976 Levy performed one of the first studies to investigate whether antibiotics fed to animals could affect human beings. When the antibiotic tetracycline was laced into the chicken feed on a farm in Sherborn, the animals began carrying resistant bacteria in their intestines within a week. Over the next six months, seven out of 11 people who lived or worked on the farm began carrying resistant bacteria as well.
And in a 2002 report, researchers in Denmark showed that the bacteria can thrive for days in human intestines. The researchers fed an innocuous strain of bacteria to a group of volunteers. The volunteers did not suffer any health consequences, according to the study, but the bacteria survived and multiplied in their intestines for two weeks.
And a study in the current issue of PLoS Medicine suggests the problem has been underestimated. According to lead author David Smithcq and other researchers at the National Institutes of Health, farms are a bigger source of resistant strains of bacteria than are hospitals.
Smith's study largely applies to bacteria such as campylobacter and salmonella that affect the digestive system, commonly causing diarrhea and very rarely leading to death.
But it's the antibiotic resistance to bacteria that cause pneumonia, tuberculosis, and blood infections that worry doctors most -- and most of that resistance seems to come from overprescribing the drugs to people, he said.
''You should be much more concerned about antibiotics that your doctor gives you," said Smith. ''Medical prescription is a far bigger problem than the agricultural overuse."Boston Globe
