LAB in the Gastrointestinal Tract

Although it is impossible to describe all microbial interactions in the GI tract, some information has been discovered about the interactions of LAB supplementation and the impact on the GI tract microflora and inhibition of food-borne pathogens. We know that the carbohydrate concentration of a diet fed to an animal is changed as it passes through the GI tract, making an in vitro model inadequate to predict the behavior of LAB in a live animal (Fuller, 1992). Model systems have been developed but may not exactly 

After ingestion of any microorganism by a host animal, it can become established in the animal or eliminated. When the microorganism becomes established, it can be at high or low population levels (Fuller, 1992). Ducluzeau et al. (1970) described the barrier effect, which is a condition in the intestinal tract that protects the host from colonization by outside microorganisms. The barrier is established after birth with a small number of bacterial species, and over time, new species will be established. Some of the species involved in colonization have been well documented and are not discussed in this chapter. The barrier can be very important with respect to the administration of a DFM. The DFM must be administered daily to become established as one of the organisms in the natural barrier if it is to continuously provide the desired effects (i.e., suppression of a food-borne pathogen). 

Work in gnotobiotic animals has suggested that production of inhibitory substances is at least partially responsible for microbial antagonism, so it is important to select strains that produce antimicrobial products. It is essential to select LAB that have the most potential to produce the desired effect in the animal and then test the LAB in vivo to verify that the strain is effective in the animal. 

A (IgA) and immunoglobulin G (IgG) levels have been shown to be increased with administration of Lactobacillus in piglets and mice (Lessard and Brisson, 1987 Perdigon et al., 1990). These findings suggest that DFMs have the potential to modulate immunity, and their effect on systemic immune response can be used to overcome infections caused by pathogens such as Salmonella that occur in tissues away from the intestinal tract. 

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