Studies Find Meat Rife With Drug-Resistant Germs

WEDNESDAY, Oct. 18, 2001 (HealthDayNews) -- Store-bought meats are warehouses for hardy, drug-resistant germs that likely sap the already flagging effectiveness of many antibiotics, new research says.

Three new studies show that pork, ground beef and poultry frequently carry strains of bacteria resistant to the antibiotics used to fight human infections. The same drugs or their close relatives are sometimes used to treat infection and prevent outbreaks of disease among livestock. More often, though, they're added to feed to bulk up animals, who tend to grow more when given the drugs in low doses.

But some experts say that in light of the latest findings, which appear today in The New England Journal of Medicine, that practice should be greatly curtailed or even stopped.

By overusing antibiotics in animal feed, "we are not only seeing illness [in humans] by specific resistant germs, but we are also adding to the pool of resistant genes" that can jump into other bacteria, says Dr. Sherwood Gorbach, a Tufts University infectious disease expert and author of an editorial accompanying the journal articles.

Gorbach cites an estimate by the Union of Concerned Scientists, which claims that animal farms use more than 24 million pounds of antibiotics each year for "non-therapeutic" purposes. That's compared to 2 million pounds used for treating or preventing disease, although the livestock industry disputes those figures. Humans, by comparison, take 3 million pounds of antibiotics annually, and a large share of those doses are unnecessary and also contribute to resistance.

Gorbach calls the situation a matter of "grave concern" and says the new studies merely add to a thick catalog of evidence that animal drugs are putting people at risk of souped-up forms of food-borne illnesses. "The data speak for themselves," he says.

Recent aggressive efforts at the slaughterhouse, including stricter surveillance and steam treating and other technologies that kill bacteria, have significantly trimmed the prevalence of such germs on carcasses, experts say. But scientists know much less about how much meat is tainted, either before shipping or at stores.

One new study, led by David White of the Food and Drug Administration (FDA), sought to address that question.

Testing 200 packages of ground pork, beef and poultry from supermarkets in the Washington, D.C., area , White's group found one in five samples contaminated with at least one of 13 strains of salmonella bugs, a leading cause of food poisoning.

Of those strains, 84 percent were immune to at least one antibiotic, and more than half were resistant to three or more drugs, particularly older medications such as tetracycline and streptomycin. Also, 16 percent of the germ samples couldn't be killed with ceftriaxone, the "drug of choice" for treating salmonella infection in children. White says that was an unpleasant "surprise."

The FDA is reviewing its policies regarding the "prudent use" of antibiotics in animal husbandry, but White declined to say where the agency is in its deliberations. The results of his study do suggest, however, that food inspectors should start looking at meat in stores as well as at slaughterhouses, he says.

In a second study, researchers at the Centers for Disease Control and Prevention (CDC) found more than half of chickens bought at stores in four states had strains of Enterococcus faecium bacteria with "low-level" resistance to the drugs quinupristin and dalfopristin.

The two medications, called streptogramins, are used to treat people with E. faecium illness that doesn't respond to another drug, vancomycin. The two drugs also are related to a compound called virginiamycin, which is commonly added to poultry feed in small doses to promote growth.

Although resistance to quinupristin and dalfopristin was common in germs on chicken carcasses, the researchers saw only three cases of resistant E. faecium in stool samples from 334 volunteers, suggesting that the problem wasn't grave yet for people.

However, they say the spread of quinupristin-dalfopristin-resistant germs in food could increase as the use of these drugs rises. If it does, they say tighter restrictions on the use of virginiamycin in livestock might be warranted. In 2001, chicken farmers fed an estimated 192,000 pounds of the drug to their birds.

Richard Lobb, a spokesman for the National Chicken Council, which represents poultry producers, says virginiamycin doesn't pose a drug-resistance threat. The CDC researchers could find "almost no impact" from the compound on germs that reach humans, says Lobb. He says the industry wouldn't consider restricting its use of feed drugs until "sound science" turns up hard evidence for such a move.

Ron Phillips, a spokesman for the Animal Health Institute, which represents livestock drug and vaccine makers, says reducing or banning antibiotics in feed isn't the best way to control resistant germs. He says a better strategy is to improve pathogen surveillance at meat plants and other, "targeted" steps to control germs.

Lobb says that fluoroquinolones -- powerful drugs that include Cipro, which is prescribed to fight anthrax and other serious infections -- are used to control outbreaks of respiratory infections in only about 1 percent of the nation's 8 billion-odd meat chickens raised each year.

That works out to about 80 million birds taking the drugs for some period of time and Gorbach calls that "a lot of chickens." He says the introduction of fluoroquinolones into animal feed was followed by a spike in the number of cases of fluoroquinolone-resistant Campylobacter, a potentially menacing poultry-borne infection.

Meat industry representatives argue that thorough cooking of meats will kill any germ, including those that resist antibiotics. But Gorbach points out that despite ever-increasing admonitions by food safety officials to the public, millions of Americans suffer bacterial food poisoning each year.

In 1999, for example, there were 1.4 million cases of salmonella and 2.4 million cases of Campylobacter in this country, many of which involved drug-resistant strains of germs.

And as a Danish study also appearing in the journal shows, drug-resistant germs can hang around in the guts of people who eat them for up to two weeks.

What To Do

While you can't tell if the meat you buy is free from dangerous germs, always assume that it isn't. Wash your hands, utensils and cutting surfaces thoroughly after they've touched raw meat, and make sure you cook it well before eating. If you're not sure, buy a meat thermometer.

To find out more about how bacteria become resistant to antibiotics, try the U.S. Food and Drug Administration or the CDC.

The National Antimicrobial Resistance Monitoring System has the latest figures on drug-resistant bugs in the nation's food supply.

For more on food safety and how to reduce your risk of food poisoning, check the U.S. government's FoodSafety Web site.