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ABSTRACT

Cells of three strains of Listeria monocytogenes, one a reference strain ATCC 19115 and two strains isolated from meat, were cold shocked at refrigeration (+4C) and freezing (−20C) temperatures during one night. Then, their fatty acids were extracted and their composition identified by gas chromatography coupled with mass spectrometry. The results showed that low thermal adaptation response of L. monocytogenes ATCC 19115 was different from that of the two recent food isolates L. monocytogenes. The three experimented strains showed a decrease of anteiso-C17:0 and an increase of anteiso-C15:0 rates. In addition, after freezing, the cellular fatty acids were detected as a signature of the membrane changes that give rise to such authenticity. The structural modification seems to be an adaptation form, allowing intracellular ice crystallization enhancement during freezing and water mobility during storage. These results demonstrated that the L. monocytogenes studied strains showed various behaviors regarding low-temperature stress maintaining membrane fluidity.

PRACTICAL APPLICATIONS

Listeria monocytogenes is prevalent in a variety of foods and ready-to-eat products; it may generate a serious public health problem. Nowadays, ready-to-eat, chilled and frozen food consumption is continuously increasing. Bacterial strains that can survive at extremely low temperatures adopt special physiological strategies, although the cold-regulated fatty acid (FA) adjustment is a universal adaptation to low temperatures. To counteract this phenomenon, L. monocytogenes modifies its plasmatic membrane structure to maintain its fluidity at low temperatures, allowing an optimum membrane fluidity that is crucial for bacterial survival. Our study suggested that after freezing, these bacteria underwent several modifications, which are especially critical because they negatively affect bacterial viability and physiological state and induce mechanical damage that leads to cellular death to fight against food invasion with these bacterial species. This work demonstrates the possibility of using membrane FA composition to characterize L. monocytogenes stress-state as an efficient tool for traceability.