Abstract
Listeria monocytogenes is a food-borne pathogen that can grow at very low temperatures close to the freezing point of food and other matrices. Maintaining cytoplasmic membrane fluidity by changing its lipid composition is indispensable for growth at low temperatures. Its dominant adaptation is to shorten the fatty acid chain length and, in some strains, increase in addition the menaquinone content. To date, incorporation of exogenous fatty acid was not reported for Listeria monocytogenes. In this study, the membrane fluidity grown under low-temperature conditions was affected by exogenous fatty acids incorporated into the membrane phospholipids of the bacterium. Listeria monocytogenes incorporated exogenous fatty acids due to their availability irrespective of their melting points. Incorporation was demonstrated by supplementation of the growth medium with polysorbate 60, polysorbate 80, and food lipid extracts, resulting in a corresponding modification of the membrane fatty acid profile. Incorporated exogenous fatty acids had a clear impact on the fitness of the Listeria monocytogenes strains, which was demonstrated by analyses of the membrane fluidity, resistance to freeze-thaw stress, and growth rates. The fatty acid content of the growth medium or the food matrix affects the membrane fluidity and thus proliferation and persistence of Listeria monocytogenes in food under low-temperature conditions.
Highlights
Listeria monocytogenes is a food-borne pathogen that can grow at very low temperatures close to the freezing point of food and other matrices
Exogenous fatty acids have already been detected in the fatty acid profile of L. monocytogenes[25], there is no experimental evidence for incorporation in the membrane and the adaptive effect of exogenous fatty acids
Both fatty acids could not be synthesized by L. monocytogenes and represent lipids with a high and a low melting temperature (Tm), 69.3 °C for C18:0 and 12.8 °C for C18:1 cis 9
Summary
Listeria monocytogenes is a food-borne pathogen that can grow at very low temperatures close to the freezing point of food and other matrices. Incorporated exogenous fatty acids had a clear impact on the fitness of the Listeria monocytogenes strains, which was demonstrated by analyses of the membrane fluidity, resistance to freeze-thaw stress, and growth rates. The fatty acid content of the growth medium or the food matrix affects the membrane fluidity and proliferation and persistence of Listeria monocytogenes in food under low-temperature conditions. Correct acyl chain composition of the membrane is crucial for the survival of L. monocytogenes in the environment, and modification of this composition by exogenous fatty acids affects the fitness of this bacterium This observation reveals a so far unconsidered impact of the lipid composition of the growth matrix on the growth and robustness of L. monocytogenes under low-temperature conditions. The potentially beneficial effect of food lipids on L. monocytogenes membranes may explain the successful colonization of many fatty food matrices stored under low-temperature conditions
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