Cellular interactions of probiotic bacteria with porcine intestinal and progenitor immune cells

Abstract

Probiotic bacteria have been shown to convey health benefits to hosts and are included in a large number of food and beverage products. The enhancement of immunological activity is one of the proposed health benefits conveyed by probiotic bacteria. At the molecular level, the mechanisms that mediate the immune cell responses to probiotic bacteria remain undefined. Studying the intracellular responses of immune cells to probiotic stimulation may provide insights into molecular events associated with enhanced immunological activity. This thesis utilises the expression of fluorescent proteins genes and subsequent generation of fluorescent proteins as a bio-indicator of immune intracellular responses to probiotic bacteria. Real-time analysis of fluorescent protein expression models has been performed using advanced fluorescence microscopy systems such as laser scanning confocal microscopy (LSCM). Coupling LSCM data with a relatively novel image analysis technique, raster image correlation spectroscopy (RICS), provides the ability to measure intracellular dynamics. The viability of probiotics in food and beverages must be maintained to ensure the health promoting activities in hosts. Food processing and storage procedures have been found to compromise the viability of probiotics. Microencapsulation of probiotic bacterial strains has been suggested to protect fragile probiotic strains. Microencapsulation has also been associated with a higher viability when compared to free cells in simulated gastrointestinal conditions. The effects of the microencapsulated environment on the probiotic bacterial behaviour has not been described. This thesis utilises the fluorescent protein expression immune cell model and fluorescent microscopy analysis as a downstream indicator of stress-related responses exhibited by the microencapsulated probiotic cells. In this study, the ability of microencapsulated probiotic bacteria to survive confinement was investigated. Microencapsulated probiotics were observed to survive and proliferate following 24 h incubation. A viability standard curve was developed for microencapsulated bacteria using the probiotic strains Lactobacillus acidophilus LAFTI L10 bacteria, Bifidobacterium lactis HN019 (DR10[Trade Mark]) and the pathogenic strain, Streptococcus pyogenes, the LIVE/DEAD BacLight[Trade Mark] bacterial viability kit, LSCM and the image analysis software, Bitplane Imaris. The microencapsulated bacteria were co-cultured with adaptive immune cells to determine stress-related changes by the confined bacteria cells. Probiotic bacterial affects on adaptive immune cells were shown to be dependent on the immune cell type (i.e. T and B cell), probiotic strain, presence of intestinal cells and if the probiotic strain was microencapsulated. Observing changes in the intracellular milieu of the immune cells treated with the free and microencapsulated bacteria is possible using fluorescent protein bio-indicator systems. Future advancements in fluorescence microscopy and image analysis software will provide further in-depth information of intracellular environmental responses to probiotic bacteria treatments.

Date of Award	2011
Original language	English