The College of Food, Agricultural, and Environmental Sciences at Ohio State University says consumers who buy ground beef labeled as “raised without antibiotics” don’t always get what they bargained – and likely paid a higher price — for.
A study conducted by Ohio State University food-animal health researcher Jeff LeJeune found similar numbers of food-borne pathogens and antimicrobial-resistant bacteria in samples of ground beef from conventionally reared cattle and from those whose labels claimed to have come from cows that didn’t receive any antimicrobial agents.
“At the microbiological level, there was little difference between both sample groups as far as presence of pathogens or resistant organisms,” said LeJeune, a scientist with the Food Animal Health Research Program (FAHRP) on the Ohio Agricultural Research and Development Center’s (OARDC) Wooster campus. “It’s incredible how close these numbers came out.”
LeJeune analyzed 150 ground-beef samples (77 conventional, 73 antibiotic-free) bought at retail stores in Ohio, Florida and Washington, D.C. between Jan. 1 and Feb. 28, 2003. While some samples were frozen and others fresh at the time of purchase, all of them were frozen at minus-20 degrees Celsius prior to testing to ensure a uniform analysis — freezing can damage bacteria and result in a lesser pathogen count.
The beef was cultured and tested for coliforms, E. coli, E. coli O157, Shiga toxin 2-producing E. coli, Salmonella and vancomycin-resistant enterococci. The results: 75.3 percent of conventional beef and 75.3 percent of antibiotic-free beef was contaminated with coliforms; 32.5 percent of conventional and 31.5 percent of antibiotic-free had E. coli; and 8.2 percent of conventional and 3.8 percent of antibiotic-free tested positive for Shiga toxin 2-producing E. coli.
Although the numbers vary somewhat, the differences are within the margin of sampling error, LeJeune said.
The level of contamination increased when the meat was cultured in a liquid medium overnight to detect even very low numbers of bacteria that may be present. Still, the difference between beef from conventional and antibiotic-free cattle was still minimal – 87 percent and 89 percent had coliforms, and 77.9 percent and 76.7 percent had E. coli, respectively.
No E. coli O157, Salmonella or vancomycin-resistant enterococci were present in any of the 150 samples.
LeJeune said the percentage of contamination and concentration of coliforms found in this study are similar to those reported in the Nationwide Federal Plant Raw Ground Beef Microbiological Survey of 1994. By contrast, E. coli contamination in this study was detected in only half as many samples as reported 10 years ago, and E. coli concentration among positive samples was lower than in the federal survey.
“This data suggest that the magnitude and frequency of contamination of ground beef with E. coli has decreased over the past decade, possibly due to the proactive efforts of the processing industry to control microbial hazards,” he pointed out.
Less E. coli in ground beef is good news. But the presence of antimicrobial-resistant bacteria, especially in the meat from cattle not fed antibiotics, is less encouraging.
Cattle in 83 percent of U.S. commercial feedlots routinely receive antibiotics for disease prevention and growth promotion during the finishing period. This practice, however, has been linked to the development of resistant bacteria, which can be transmitted through food and sicken people with infections that are more difficult or impossible to treat with those same antibiotics.
In the meantime, beef grown without antibiotics is being promoted as less likely to be tainted with antimicrobial-resistant bacteria, and a growing number of consumers are willing to pay higher prices for this assurance.
But LeJeune’s research shows that at the grocery store, ground beef by any other name can still carry antibiotic-resistant bacteria.
LeJeune cultured the same 150 beef samples looking for resistance to 11 antibiotics commonly used in cattle. Again, the difference between conventional and antibiotic-free beef samples was not significant. For example, bacteria resistant to tetracycline — one of the most commonly used antimicrobial agents in cows — was found in 18.2 percent of the conventional samples and in 19.2 percent of the antibiotic-free samples. Resistance to the antibiotic ampicillin was detected in 44.2 percent and 32.9 of the samples, respectively.
No data on resistant organisms is available from 1994 to know whether these numbers have increased, decreased or remained constant.
“The question is, why are they the same?” LeJeune said. “If the subtherapeutic (growth-promoting) use of antimicrobial agents is the sole driving force for the emergence and persistence of antimicrobial-resistant bacteria in the food supply, one would expect to find fewer antimicrobial-resistant counts in meat derived from cattle raised without the use of antibiotics for growth promotion.”
The answer probably lies elsewhere, LeJeune said. Dissemination of antimicrobial-resistant bacteria from farm to farm can occur, possibly though contaminated feed, wildlife and other environmental sources. Cross-contamination can also take place during slaughter and processing.
“Meat is sterile in the cow,” LeJeune explained. “The majority of coliforms and E. coli that contaminate cuts of beef do not necessarily originate directly from the intestinal tract of the animal from which the carcass is derived. But contamination from other carcasses being processed or processing equipment such as grinders and knives contributes significantly to the spread of bacteria. So if you slaughter and process conventionally reared animals and animals raised without antibiotics in the same place, cross-contamination can easily occur.”
LeJeune said that raising cattle without the use of antibiotics will not by itself solve the problem of antimicrobial-resistant bacteria in beef.
“From a food safety perspective,” he said, “taking away those antibiotics is not going to make a difference unless there is a concerted effort to minimize the spread of resistant bacteria among live animals and reduce bacterial cross-contamination during slaughter and processing.”
Food-borne pathogens cause an estimated 76 million cases of illness each year in the United States. Although most bacterial contaminants found in ground beef and other meat products can be destroyed by adequate cooking, 30 percent of Americans eat undercooked hamburger.
LeJeune’s study was published in the July 2004 issue of the Journal of Food Protection.
OARDC is the research arm of Ohio State’s College of Food, Agricultural, and Environmental Sciences.