Scientists find food type plays a role in Listeria survival

Researchers have studied how different food matrices affect Listeria survival and virulence in the gastrointestinal tract.

A study by the University of Veterinary Medicine in Vienna (Vetmeduni) showed that Listeria in fish and cheese are best protected from stress in the gastrointestinal tract. In sausage, the survivability of Listeria is significantly lower.

According to researchers, this is due to the different composition of the tested foods.

Scientists looked at three ready-to-eat foods: soft brie cheese, smoked salmon and heat-treated non-fermented sausage. The behavior of three Listeria strains was examined using a food infection model of the gastrointestinal tract. Findings were published in the journal npj Science of Food.

Survival in sausage

The survival rate of Listeria monocytogenes was higher in cheese and fish than in sausage, which is due to their lower buffering capacity in the gastrointestinal model.

Invasion efficiency in intestinal epithelial cells was highest after growth and passage through the model in fish, which may be related to its fatty acid composition, said scientists.

The food matrices and conditions in the gastrointestinal tract also altered the profile of stress-associated and virulence genes.

Nadja Pracser, from the Center for Food Science and Veterinary Public Health at Vetmeduni, said: “We observed strain-dependent growth rates, whereby the food matrix had no significant influence, but the type of nutrient source changed the gene expression. However, the respective food clearly influenced the survival of Listeria in the gastrointestinal tract and also the virulence.”

The model included the growth of Listeria monocytogenes in RTE food at low temperature storage conditions, a three-steps in vitro digestive model, and an in vitro virulence assay.

Role of fat and protein
While food type did not significantly affect bacterial growth after seven days at 10 degrees C (50 degrees F), notable differences were seen among the strains.

When comparing the log reduction after the oral phase, scientists observed significant differences between both the strains and the food items. Following the gastric phase, there were differences in log reduction between sausage and cheese, as well as between sausage and fish. Upon comparing the log reduction after the intestinal phase, which represented the final stage in the model, there were differences between sausage and both cheese and fish. 

According to researchers, changing the fat and protein content in foods could help reduce the survivability of Listeria monocytogenes in the gastrointestinal tract and improve food safety.

“The results of our study also suggest that the properties of smoked salmon in combination with the conditions in the gastrointestinal tract increase virulence. The fact that the food matrix has a direct influence on the behavior and pathogenic potential of Listeria monocytogenes underlines the importance of understanding these interactions for food safety and public health,” said Kathrin Kober-Rychli, from the Center for Food Science and Veterinary Public Health at Vetmeduni.

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