The meat, which was sold under 80 different brands, was purchased in Los Angeles; Chicago; Washington, D.C.; Fort Lauderdale; and Flagstaff, Ariz. The variety and number of S. aureus strains found on the samples suggest that the livestock themselves—rather than contamination during processing and packaging—are the source of the bacteria, the study notes.
Each year farmers and ranchers give millions of pounds of antibiotics to farm animals, most of them healthy, to make them grow faster and to prevent—rather than treat—diseases, says Price, the director of the Center for Food Microbiology and Environmental Health at the Translational Genomics Research Institute, a nonprofit organization in Flagstaff.
The combination of bacteria, antibiotics, and livestock living in close quarters creates the perfect environment for bacteria to thrive and mutate, which may explain the high levels of drug-resistant S. aureus seen in the study, he adds.
Virtually all (96%) of the S. aureus strains Price and his colleagues isolated had developed resistance to at least one antibiotic. Strains resistant to three or more antibiotics were found in 79% of turkey, 64% of pork, 35% of beef, and 26% of chicken samples.
“It’s four different meats from four different animals in different geographical areas,” Bowden says. “[S. aureus] may be more prevalent than we think.”
Methicillin-resistant S. aureus (MRSA), which has been a particular menace to humans in hospitals and communities alike, was found in one package each of beef, turkey, and pork, though not chicken. This sample size wasn’t large enough to arrive at an accurate estimate of its prevalence in meat nationwide, according to the study.
The Centers for Disease Control and Prevention, the Food and Drug Administration, and the U.S. Department of Agriculture currently monitor the country’s meat supply for evidence of four major types of antibiotic-resistant bacteria (including Salmonella and E. coli). The study findings suggest that S. aureus should be screened for regularly as well, the researchers say.
James H. Hodges, the president of the American Meat Institute Foundation, the research arm of a national trade association for meat suppliers, said in a statement that the number of meat samples used in the study was too small to be representative of the nation’s food supply. “Consumers can feel confident that meat and poultry [are] safe,” Hodges said. “Federal data show that S. aureus infections in people that are caused by food are uncommon.”