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Molecular genetics


Molecular genetics could shed new light on beef spoilage

The challenge: Characterization and enumeration of spoilage organisms on beef using novel molecular techniques.

The researchers: Dr. Frances Nattress and Dr. Chris Yost, Agriculture and Agri-Food Canada (AAFC) Lacombe Research Centre.

Funding allocation.

The Canada Alberta Beef Industry Development Fund (CABIDF) will distribute $16.4 million to research projects specific to the needs of Alberta cattle producers. CABIDF has allocated $38,400 to this project.

Meat spoilage is a significant concern for the Canadian beef industry, with related costs estimated at $200 million per year. With support from the Canada Alberta Beef Industry Development Fund, researchers will use genetic technology to explore the intricate world of lactic acid bacteria in order to find out more about beef spoilage.

“We’re interested in learning more about some of the processes that occur during spoilage and some of the organisms that grow on the meat,” says lead researcher Dr. Frances Nattress, a meat microbiology scientist with Agriculture and Agri-Food Canada’s Lacombe Research Centre. “In the future, we can use this research as a foundation to look at ways of controlling these organisms.” The lactic acid bacteria are a very hardy and versatile group of organisms. Their growth is difficult to control and they are resistant to environmental conditions that would inhibit most other bacteria such as low pH, refrigeration temperatures and packaging in the absence of oxygen.

Previous research has shown that lactic acid bacteria are the primary bacteria in vacuum-packaged meat and that with extended refrigerated storage, their numbers attain high levels and spoilage ensues. Currently, vacuum packaging is used to market about 80 percent of Canadian beef to domestic and international markets, Nattress says. Scientists know that lactic acid bacteria contribute to meat spoilage, but their understanding of which bacteria contribute to that process or how they contribute is limited.

The challenge is that researchers so far have little information about meat-borne lactic acid bacteria. Because the bacteria look very much alike as they grow and have similar metabolic activity, it is difficult and time consuming to differentiate between them using standard microbiological techniques. “Right now we’re really shooting in the dark; because although we have some preliminary information, we don’t know how different groups of these bacteria are related to factors such as flavour changes,” she says. “This research will give us quite a bit of information about what is happening. That will help us to pinpoint areas that we might target, possibly for antimicrobial treatments.”

“What we would like to do is develop techniques that rely on the genotype of the organism, rather than the phenotype,” she says. “We’ll be looking at DNA sequences that are specific to certain organisms. We hope that approach will be the key to unlocking that black box of unknown surrounding the lactic acid bacteria and allow us to develop a system to identify them very quickly and reliably as they grow.”

Marker will help track bacteria

Researchers are planning to develop a molecular marker for the lactic acid bacteria which would allow them to track the bacteria. With the marker, they could follow a labeled organism when it is introduced to natural flora, to ascertain how it grows in a competitive environment, how it reacts to antimicrobial treatments and to possibly visualize it on the meat surface.

To begin the study, researchers will select DNA sequences that are specific to each of the four or five groups of lactic acid bacteria that are found on meat. These sequences will anneal to the DNA of a specific type of organism and not with any of the others. Scientists will store a quantity of meat in vacuum packages at refrigeration temperatures. They will remove one package of meat from storage each week for six weeks and using these specific DNA sequences to differentiate the organisms, they will enumerate how many of each type of lactic acid bacteria is present in the meat.

Parallel to that, scientists will develop a vector, or transport system, that can carry green fluorescent protein (GFP) into Gram positive bacteria, such as the lactic acid bacteria. The GFP, which is derived from a certain type of jellyfish, will act as a sort of “molecular highlighter.” Once inserted into an organism, it will express a green fluorescent pigment that can be seen under ultra-violet light.

“The GFP will be inserted randomly into the chromosome,” she says. “So, depending where it goes on the chromosome, we can monitor when the organism ‘turns on’ certain types of genes. Related to spoilage, we can then look at whether the organism is changing its gene expression as the meat spoils. We can also find the organism in a mixed population of bacteria.”

Test for lactic acid bacteria in meat

The main focus of this part of the project is to develop the system to transport GFP to Gram positive bacteria. If resources permit, Nattress says scientists will then test that system on lactic acid bacteria in meat.

This study should give researchers a solid foundation of knowledge of lactic acid bacteria that can be applied to other projects aimed at inhibiting spoilage organisms on beef.

“It’s going to give us a much broader understanding of exactly what’s happening in terms of the succession of lactic acid bacteria on meat and what their roles in the spoilage process might be,” Nattress says. “Eventually, we may be able to determine when, during meat processing, the lactic acid bacteria associated with meat spoilage are deposited on the meat. We should have a thorough understanding of the role of different lactic acid bacteria in the spoilage process with the goal of controlling or inhibiting them.”