LOS ANGELES -- Meat in the U.S. may be widely contaminated with strains of drug-resistant bacteria, researchers reported Friday after testing 136 samples of beef, chicken, pork and turkey purchased at grocery stores.
Nearly half of the samples -- 47 percent -- contained strains of Staphylococcus aureus, the type of bacteria that most commonly causes staph infections. Of those bacteria, 52 percent were resistant to at least three classes of antibiotics, according to a study published in the journal Clinical Infectious Diseases.
DNA testing suggested the animals were the source of contamination. Environmental health scientist Lance Price, the study’s leader, said the animals most likely harbored these drug-resistant pathogens because they are fed to livestock to promote growth and prevent disease in crowded pens on large farms.
“These findings really point to serious problems with the way food animals are raised in the U.S. today,” said Price, who directs the Center for Food Microbiology and Environmental Health at the Translational Genomics Research Institute, a nonprofit biomedical research center in Phoenix.
Last summer, the Food and Drug Administration urged the meat industry to cut back on antibiotic use out of concern that the practice breeds drug-resistant bacteria in stockyards makes antibiotics less effective in humans.
But other scientists said it was premature to conclude that antibiotics in animal feed were to blame. About half of all humans have staph bacteria in their nose or throat, and a food handler with poor hygiene could introduce the pathogen to the food supply, said Beilei Ge, a food scientist at Louisiana State University in Baton Rouge.
The meat and poultry samples tested in the study represented 80 brands and were purchased in Los Angeles, Chicago, Fort Lauderdale, Fla., Flagstaff, Ariz., and Washington, D.C.
Scientists incubated the samples for up to 24 hours in a broth that was kept at human body temperature and used genetic tests to determine whether they contained the staph bacteria. Then they treated them with vancomycin, oxacillin, tetracycline and other antibiotics to determine whether they were resistant to the drugs.
The research was funded by the Pew Campaign on Human Health and Industrial Farming, which advocates against the routine use of antibiotics in animal feed.
About 11,000 people die every year from S. aureus infections, according to the Centers for Disease Control and Prevention, and more than half of those deaths are from the hospital “superbug” methicillin-resistant S. aureus, or MRSA.
The direct risk that consumers will acquire a staph infection from meat can be reduced by cooking meat thoroughly and washing all foods and surfaces that come into contact with raw meat, whether or not they are resistant to antibiotics.
However, Caroline DeWaal, director of food safety at the Center for Science in the Public Interest in Washington, said the study results suggest that consumers might benefit by wearing gloves when they handle raw meat. “It’s making us rethink our advice to the public,” she said.
The American Meat Institute, which represents producers, said Friday that the country’s meat and poultry supply is safe and the study is misleading. And data from the CDC show that cases of food-borne illness in the U.S. have declined 20 percent in the past decade.
“Despite the claims of this small study, consumers can feel confident that meat and poultry is safe,” said James H. Hodges, the organization’s president.
Federal data from the CDC show steady declines in foodborne illnesses linked to consumption of meat and poultry overall and indicate that human infections with Staphylococcus aureus (“Staph”) comprise less than one percent of total foodborne illnesses.
While the study claims that the many of the bacteria found were antibiotic resistant, it does note that they are not heat resistant. These bacteria are destroyed through normal cooking procedures, which may account for the small percentage of foodborne illnesses linked to these bacteria. As with any raw agricultural product, it is important to follow federal safe handling recommendations included on every meat and poultry package that urge consumers to wash hands and surfaces when handling raw meat and poultry and to separate raw from cooked foods to ensure that food is safe when served.
