The type of food influences the behaviour of Listeria monocytogenes in a food-gastrointestinal-infection model

Abstract

Food contaminated with Listeria (L.) monocytogenes is the main source of human listeriosis, but how different food matrices affect the survival and invasion in the gastrointestinal (GI) tract is still unclear. This study examined three ready-to-eat foods - soft-cheese, smoked salmon, and sausage - using a food-GI-infection model. We observed strain-dependent growth rates, but food matrices did not significantly impact growth. However, nutrient sources altered gene expression. Passage through the GI model upregulated 23 stress genes and 29 virulence genes (e.g., clpE, hly, and plcB). L. monocytogenes survival was higher in cheese and fish compared to sausage, due to their lower buffer capacity. Invasion efficiency into Caco-2 cells was highest in fish, potentially linked to its fatty acid composition. Food matrices and GI conditions influenced the transcriptional profiles of stress-associated and virulence genes. This study highlights the significant role of food matrices in L. monocytogenes survival and infection.

Fig. 1. Growth of L. monocytogenes in different food matrices.

Boxplot for log increase split into the different food matrices (a) and the different strains (d). Interaction plot for log increase showing interactions of the different food matrix depending on the strain (b) and of the different strains depending on the food matrix (c). Black: cheese (n = 9), blue: fish (n = 9), red: sausage (n = 9), grey: EGDe (n = 9), green: QOC1 (n = 9), orange: R479a (n = 9). *p < 0.05.

Fig. 2. Survival of L. monocytogenes after the intestinal phase.

Boxplot for log reduction split into the different food matrices (a) and the different strains (d). Interaction plot for log reduction showing interactions of the different food matrix depending on the strain (b) and of the different strains depending on the food matrix (c). Black: cheese (n = 9), blue: fish (n = 9), red: sausage (n = 9), grey: EGDe (n = 9), green: QOC1 (n = 9), orange: R479a (n = 9). *p < 0.05.

Fig. 3. Invasion of L. monocytogenes surviving the intestinal phase.

Boxplot for invasion efficiency (%) split into the different food matrices (a) and the different strains (d). Interaction plot for invasion efficiency (%) showing interactions of the different food matrix depending on the strain (b) and of the different strains depending on the food matrix (c). Black: cheese (n = 18), blue: fish (n = 18), red: sausage (n = 18), grey: EGDe (n = 18), green: QOC1 (n = 18), orange: R479a (n = 18). *p < 0.05.

Fig. 4. Principal component analysis (PCA) of L. monocytogenes transcriptomic data.

Variance stabilizing transformation (vst) was performed before conducting PCA. Yellow star: Inoculum (n = 3); Black dot: after seven-day growth in cheese (n = 3); Blue dot: after seven-day growth in fish (n = 2); Red dot: after seven-day growth in sausage (n = 3); Black triangle: after passage through the GI model in cheese (n = 3); Blue triangle: after passage through the GI model in fish (n = 2); Red triangle: after passage through the GI model in sausage (n = 3).

Fig. 5. Gene set enrichment analysis (GSEA) for L. monocytogenes transcriptomic data after growth in food matrices for seven days.

Ridgeplot showing enriched KEGG pathways (p adj < 0.05) in the full L. monocytogenes transcriptome after seven-day growth in sausage versus cheese (a), after seven-day growth in sausage versus fish (b), after seven-day growth in fish versus cheese (c).

Fig. 6. Differential gene expression of L. monocytogenes after GI stress in food matrices compared to growth in food for seven days.

Changes in the gene expression of L. monocytogenes (p adj < 0.05, log2FoldChange ≥ |2|) of virulence and stress resistance genes in sausage, fish, and cheese after passage through the artificial GI model compared to growth in the three food matrices for seven days.

Fig. 7. Effect of the food matrix on differential gene expression of stress and virulence genes of L. monocytogenes after GI stress.

Differences in gene expression (p adj < 0.05, log2FoldChange ≥ |2|) of stress and virulence associated genes (custom-made stress and virulence related gene database) in L. monocytogenes in sausage, fish and cheese after the passage through the GI-model.

Fig. 8. Effect of the food matrix on differential gene expression of L. monocytogenes after GI stress.

Differences in gene expression (p adj < 0.05, log2FoldChange ≥ |2 | ) of bacteriophage genes (a) and of selected stress associated genes (KEGG annotation) (b) in L. monocytogenes in sausage, fish and cheese after the passage through the GI-model.