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Discovering how Listeria grows on refrigerated salmon

By Tim Sandle     Aug 12, 2015 in Science
Listeria monocytogenes, in sufficient numbers on refrigerated food, can present the serious risk of listeriosis. Researchers have been investigating the growth mechanism of the bacterium to find a way of reducing infection rates.
Listeriosis is an infection that usually develops after eating food contaminated by Listeria bacteria, of which Listeria monocytogenes is the most common (but not the only) infectious agent. The disease targets the central nervous system (regions such as the meningitis, meningoencephalitis, brain abscess, cerebritis) and can cause bacteremia, which is a particular risk to the immunocompromised, pregnant women and the very young or elderly.
Listeria cases regularly appear in the press. Digital Journalist Karen Graham has highlighted two important ones recently, which have led to food recalls. These were Brenham, Texas-based Blue Bell Creameries, in the U.S.; and Sun Rich Fresh Foods, Inc., in Canada. In these types of cases there has been a breakdown in quality standards.
To investigate the transmission of the bacterium in relation to chilled food, a research group examined the metabolic pathways that the bacterium uses to grow. Here it was found that L. monocytogenes grows on a common foodstuff like chilled smoked salmon by using different metabolic pathways to obtain its energy to those it uses to grow on culture media in a microbiology laboratory.
On salmon, the bacterium uses altered genes. These modified (or "upregulated") genes allow the organism to make use of two compounds from cell membranes as sources of energy. These compounds are ethanolamine and propanediol. Parallel research has shown another food poisoning organism — Salmonella — to make use of the same genes.
It is hoped that this understanding, about how the infectious organism grows under cold conditions on food, can be the basis of a mechanism to control it. This could be by using a chemical inhibitor which is added to food to slow down the bacterium’s metabolic activity, as an example. Such an inhibitor could be something relatively natural, like an organic acid.
Such measures should not replace good hygiene practices during food processing. Listeria is a risk when it is present in high numbers and given the opportunity to grow under cold storage.
The research has been published in the journal Applied and Environmental Microbiology. It is headed “Transcriptomic analysis of Listeria monocytogenes Adaptation to Growth on Vacuum-Packed Cold Smoked Salmon.”
More about Listeria, Bacteria, Salmon, Food poisoning
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