Mortality and translocation assay to study the protective capacity of Bifidobacterium lactis INL1 against Salmonella Typhimurium infection in mice.

The mouse has been largely used for the study of the protective capacity of probiotics against intestinal infections caused by Salmonella. In this work we aimed at comparing the mortality and translocation assay for the study of the protective capacity of the human breast milk-derived strain Bifidobacterium animalis subsp. lactis INL1 on a model of gut infection by Salmonella enterica subsp. enterica serovar Typhimurium. Different doses of S. Typhimurium FUNED and B. animalis subsp. lactis INL 1 were administered to Balb/c mice in a mortality or a translocation assay. The survival of the control group in the mortality assay resulted to be variable along experiments, and then we preferred to use a translocation assay where the preventive administration of 109 cfu of bifidobacteria/mouse for 10 consecutive days significantly reduced the number of infected animals and the levels of translocation to liver and spleen, with enhanced secretory immunoglobulin A and interleukin 10 production in the small and large intestine, respectively. Ten days of B. animalis subsp. lactis strain INL1 administration to mice significantly reduced both the incidence and the severity of Salmonella infection in a mouse model of translocation. This work provided the first evidence that a translocation assay, compared to a mortality assay, could be more useful to study the protective capacity of probiotics against Salmonella infection, as more information can be obtained from mice and less suffering is conferred to animals due to the fact that the mortality assay is shorter than the latter. These facts are in line with the guidelines of animal research recently established by the National Centre for the Replacement, Refinement & Reduction of Animals in Research.

Cell viability and immunostimulating and protective capacities of Bifidobacterium longum 51A are differentially affected by technological variables in fermented milks.

AIM: To investigate the cell viability of Bifidobacterium longum 5(1A) in fermented milks and to study its immunostimulating and protective capacity against Salmonella enterica ssp. enterica serovar Typhimurium infection in mice. METHODS AND RESULTS: Bifidobacterium longum 5(1A) was added to milk fermented with different yoghurt starter cultures, before or after fermentation, and viability was monitored during storage (5°C, 28 days). Resistance to simulated gastric acid digestion was assessed. Fermented milks were orally administered to mice for 10 days followed by oral infection with Salmonella Typhimurium. The number of IgA+ cells in the small and large intestine was determined before infection. Survival to infection was monitored for 20 days. Bifidobacterium longum 5(1A) lost viability during storage, but the product containing it was effective for the induction of IgA+ cells proliferation in the gut and for the protection of mice against Salm. Typhimurium infection. CONCLUSIONS: Cell viability of Bif. longum 5(1A) in fermented milks along storage did not condition the capacity of the strain to enhance the number of IgA+ cells in the gut and to protect mice against Salmonella infection. SIGNIFICANCE AND IMPACT OF THE STUDY: The uncoupling of cell viability and functionality demonstrated that, in certain cases, nonviable cells can also exert positive effects.

Preservation of functionality of Bifidobacterium animalis subsp. lactis INL1 after incorporation of freeze-dried cells into different food matrices.

The aim of this work was to investigate how production and freeze-drying conditions of Bifidobacterium animalis subsp. lactis INL1, a probiotic strain isolated from breast milk, affected its survival and resistance to simulated gastric digestion during storage in food matrices. The determination of the resistance of bifidobacteria to simulated gastric digestion was useful for unveiling differences in cell sensitivity to varying conditions during biomass production, freeze-drying and incorporation of the strain into food products. These findings show that bifidobacteria can become sensitive to technological variables (biomass production, freeze-drying and the food matrix) without this fact being evidenced by plate counts.