About one of every four samples of meat and poultry from U.S. grocery stores is contaminated with drug-resistant strains of Staphylococcus aureus, according to a study published April 15 in the journal Clinical Infectious Diseases (Waters AE, Contente-Cuomo T, Buchhagen J, et al. Clin Infect Dis. 2011;52(10):1227-1230).
The study, the first national assessment of antibiotic-resistant S. aureus in the U.S. food supply, found some form of S. aureus in 47 percent of meat and poultry samples, and 52 percent of those bacteria were resistant to at least three classes of antibiotics. The samples were collected from 26 retail grocery stores in five cities: Los Angeles; Chicago; Fort Lauderdale, Fla.; Flagstaff, Ariz., and Washington, D.C.
“For the first time, we know how much of our meat and poultry is contaminated with antibiotic-resistant staph, and it is substantial,” said Lance B. Price, PhD, senior author of the study and director of the Center for Food Microbiology and Environmental Health at the Translational Genomics Research Institute, which conducted the study, in a statement.
But food safety experts questioned the significance of the study. “The numbers are clear: There is little foodborne illness from staph, and when there is, it’s often human cross-contamination,” said Doug Powell, PhD, professor of food safety at Kansas State University.
In the CDC’s 2011 estimates of pathogens contributing to foodborne illness overall in the U.S., S. aureus ranked fifth, accounting for 3 percent of cases. By comparison, Norovirus caused some 58 percent of foodborne illness outbreaks, Salmonella 11 percent, Clostridium perfringens 10 percent, and Campylobacter 9 percent.
And when broken down into cases of foodborne illness resulting in hospitalization or death, S. aureus drops off the top five list entirely, displaced by bacteria such as E. coli O157 and Listeria monocytogenes .
The study findings of extensive S. aureus contamination in meat and poultry are neither new nor surprising, said Michael Doyle, PhD, Regents Professor of Food Microbiology and director of the Center for Food Safety at the University of Georgia in Griffin. “Not only do most domesticated animals harbor S. aureus, but about 50 percent of normal, healthy human adults also carry S. aureus in their nasal cavities. Many of the S. aureus strains found in animals are of human origin.”
To actually make a person sick, extremely large numbers of S. aureus must be present in the food, Dr. Doyle said—more than a million per gram. “Meats and poultry are commonly contaminated with S. aureus, but at less than 100 cells per gram,” he explained. “Using good food handling procedures will mitigate the risk of transferring S. aureus from meats to humans. This includes washing hands after handling meat, avoiding cross-contamination of meat juices and food contact surfaces with ready-to-eat foods such as salads, and properly cooking meat according to [U.S. Department of Agriculture] recommendations.”