Antibacterial bacteria may be used in ground beef

Apr 26, 2006 (CIDRAP News) – Food stores may soon be able to offer ground beef and other meat products treated with a mixture of harmless bacteria that reportedly can reduce common pathogens by 99% or more.

The mixture contains four strains of lactic acid bacteria (LAB), a class of organisms that has long been used in cultured dairy products such as yogurt and cheese. In a study reported last year in the Journal of Food Protection, the mixture, called Bovamine Meat Cultures, progressively reduced the levels of Escherichia coli O157:H7 and Salmonella in ground beef during several days of refrigerated storage.

Last December the Food and Drug Administration (FDA) classified the product as "generally regarded as safe" (GRAS), clearing the way for commercial use. Nutrition Physiology Corp., based in Indianapolis, is preparing to market the product.

Though no company is selling meat treated with the mixture yet, "There are a number of meat companies that are doing in-plant testing with the concept," Doug Ware, president of the Indianapolis firm, told CIDRAP News.

Ware said he had expected it would take 2 years to get the FDA's safety designation, but it took only 6 months. Since then, he said, the company has been working with the US Department of Agriculture's Food Safety and Inspection Service to determine the labeling for meat products containing the mixture. Labels will say the product contains lactic acid cultures added for food safety.

Aside from the labeling issue, the product faces no major regulatory hurdles, Ware said.

"People have historically looked at individual lactic acid cultures for food safety around the world," he said. "The uniqueness of this is that any one [of the four lactic acid bacteria strains] has been effective by itself, but the combination of four is why we're seeing 3- and 4-log reductions with E coli, and as much as 5 logs with Salmonella."

A team led by Mindy Brashears, PhD, at Texas Tech University in Lubbock has developed and tested the LAB mixture, with support from beef industry groups and Ware's company. A recent Texas Tech news release called the product "one of the few post-production treatments available that protects meat and poultry during long-term storage."

In earlier research, Brashears' team identified several strains of LAB that could eliminate E coli O157, Salmonella, and Listeria monocytogenes in laboratory cultures, according to their report in the Journal of Food Protection. "These LAB are unique in that they eliminate the pathogens at refrigeration temperatures but do not grow during refrigerated storage," they wrote. "Growth of LAB in a fresh meat product would not be desirable because it would lead to premature spoilage of the product."

The team used four strains of Lactobacillus acidophilus in the study reported last year. They tested the four strains individually in refrigerated ground beef injected with E coli O157 and Salmonella and then tested a mixture of all four.

In the individual tests, the LAB strains produced an average 1.5-log (>90%) reduction in E coli after 8 days of storage, compared with control samples. The strains yielded a similar reduction in Salmonella levels after 4 days of storage.

Because 8 days is considered too long to store raw ground beef without freezing, the team mixed a cocktail of all four strains and tested it in contaminated ground beef samples, according to the report. The mixture yielded a 2-log (99%) reduction in E coli after 3 days of storage, and a 3-log (99.9%) reduction after 5 days, the report says.

The results were even better against Salmonella. The LAB mixture reduced Salmonella levels by more than 3 logs after 3 days of storage. After 5 days of storage, Salmonella was undetectable.

The researchers also examined whether the bacterial mixture affected the taste of ground beef. Tasters could not detect a difference between treated and untreated ground beef samples that had been stored for 3 days before cooking.

"The use of LAB in ground beef appears to be a promising intervention to control foodborne pathogens and might be an important critical control point in ground beef processing systems," the researchers wrote.

Exactly how LAB combat E coli and Salmonella isn't clear, according to the article. But some studies "have indicated that a protein-based product, most likely a bacteriocin [bacteria-killing chemical], is produced by these LAB isolates at refrigeration temperatures," it states.

Food safety expert Craig Hedberg, PhD, said the LAB mixture is likely to make a contribution to meat product safety, but how big a part it will play is unclear.

"As with many of the food safety technologies that have been developed in recent years, this will certainly have a role to play as part of a multi-stage approach to control," said Hedberg, who is an associate professor of environmental and occupational health in the University of Minnesota School of Public Health.

Commenting by e-mail, he said the limitation of LAB as a safety treatment "is that they may inhibit growth of the pathogens, and may cause reductions in pathogen loads, but they will not be able to eliminate the pathogens entirely. Thus, when you are dealing with pathogens that have a very low infectious dose, you may have enough pathogens surviving to be a problem. In addition, once you start handling the product, mixing it with other ingredients, etc, you may shift the 'balance of power' such that the level of control may be lessened."

This drawback could limit adoption of the product, at least for beef, Hedberg said. "Reducing populations [of E coli] 2 to 4 logs may lessen the public health burden, but if it doesn't reduce the likelihood of detecting a contaminated product, the industry may not see a benefit," he said.

See also:

Smith L, Mann JE, Karris K, et al. Reduction of Escherichia coli O157:H7 and Salmonella in ground beef using lactic acid bacteria and the impact on sensory properties. J Food Protect 2005;68(8):1587-92 [Abstract]

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