Analysis of the survival of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> in food-grade lubricants

Listeria monocytogenes is a ubiquitously occurring Gram-positive bacterium, which is associated with raw ready-to-eat foods, in particular with smoked or graved salmon. Due to its tenacity and psychrotrophic growth properties, it may persist on the equipment and machinery used in food production. In this study, we analysed the survival of three L. monocytogenes strains in eight H1 lubricants, seven greases and one oil, applicable for food-processing machinery. None of the native lubricants contained Listeria spp. above the detection limit of 10³ cfu/g. In artificially contaminated lubricants, the viable counts of different L. monocytogenes strains decreased by more than 99.9% within 7 days, and the reduction rates were found to dependent on the composition of the respective lubricant as well as on the L. monocytogenes strain. Chemical binding of either benzoate or acetate to native grease 3 caused a similar anti-listerial activity, but a decreased effect was observed when stearic acid was used. When benzoate, acetate, salicylate or parabene was added at a concentration of 0.5% to native grease 1, similar anti-listerial effects were observed. The water content (0, 1 and 5%) and the age of the lubricant did not influence the results. Used lubricants originating from dismantled industrial machinery did not contain L. monocytogenes, though this microorganism was re-isolated from the lubricants following artificial contamination. Thus, there is no evidence that L. monocytogenes replicate or persist in the H1 lubricants used in this study.