Bacteria holds key to less beef spoilage, pathogens

Cattle Market & Farm Reports, Editorials
Sep 13, 2004
by WLJ
Researchers have isolated a strain of lactic acid bacteria (LAB) with the potential to not only reduce meat spoilage, but also reduce contamination by food-borne pathogens including E. coli O157:H7 and listeria monocytogenes.
"Meat processors tell us that one of their biggest concerns is LAB," said Dr. Frances Nattress, an Agriculture and Agri-Food Canada researcher based in Lacombe. "Processors say that LAB are a frequent reason for product return, because some strains contribute to the spoilage of vacuum-packed meat, which is a $200 million per year problem for the Canadian beef industry."
Nattress and colleague Dr. Christopher Yost used molecular genetics to successfully identify the specific LAB populations that grow on vacuum-packed meat and then conducted further research to determine if specific strains have any benefits. The research was funded in part by the Canada Alberta Beef Industry Development Fund (CABIDF).
Currently about 80 percent of Canadian beef for domestic and international markets is vacuum-packed. Vacuum packing allows for a longer shelf life—vacuum-packaged beef stored at zero degrees, Celsius, can have a storage life of 10-12 weeks. For beef packaged in 100 percent CO2 stored at two degrees Celsius, the storage life can be as long as eight weeks. However, these vacuum-packaged environments often allow LAB to flourish.
"LAB are a very hardy and versatile group of organisms," said Nattress. "Their growth is difficult to control and they are resistant to environmental conditions, such as low pH, refrigeration, and packaging in the absence of oxygen, that would inhibit the growth of most other bacteria."
However, Nattress's research has led scientists to believe that one particular LAB strain could be beneficial in vacuum-packaged meat.
"We've identified one LAB strain that prevents the propagation of other spoilage-causing strains and has the ability to reduce numbers of food-borne pathogens, such as E. coli O157:H7," she said.
In week zero of the research, Nattress found a mixed LAB community on the beef, consisting of lactobacillus curvatus, lactobacillus sakei and leuconostoc spp. However, by week six, a single leuconostoc strain dominated, which demonstrated an antagonism towards the growth of all other LAB isolated during the study. Furthermore, it appeared to inhibit the growth of pathogens E. coli O157:H7 and listeria monocytogenes, both of which are significant food safety concerns.
Further DNA sequencing suggested that the isolate was a l. gelidum strain. Using molecular typing methods, researchers will be able to further probe the benefits of this l. gelidum on vacuum-packaged meat.
"Now we have to gain a better understanding of exactly how this and the other strains of LAB interact, so that we can make the best use of the positive strain, while reducing negative strains," said Nattress.
"This research has opened the door to other projects aimed at inhibiting the growth of spoilage organisms on beef, which could lead to significant savings for Canada's beef industry," she added. "Heading into the fall, we'll be doing more trials with contaminated meat, to gain an even greater understanding of how this particular strain works to reduce spoilage and food-borne pathogens. Eventually we may be able to introduce it to the beef industry as an 'ingredient' that could improve their product." — WLJ