Fig. 1

Probiotic mode of action. These include six proposed mechanisms: a Inhibition of pathogen adhesion. Probiotics improve the growth rate against pathogenic microbes by suppressing pathogenic growth and diminishing pathogenic adhesion in the gastrointestinal (GI) tract. b Secretion of defensins/bacteriocins. Probiotics can intensify antimicrobial protein secretion like defensins to eliminate pathogens. c Competitive exclusion of pathogenic microorganisms. Probiotics can rigorously compete with intestinal harmful microbes to prohibit detrimental colonization by binding with receptors in the IEC or mucus layer. d Enhancement of barrier function. Probiotics can improve mucin glycoproteins secretion by the mucus-producing cells to yield a dense mucus layer that helps to decrease intracellular permeability to pathogens. e Reduction of luminal pH. Probiotics lessen the pH level of the lumen by triggering acetic acid production which is deadly to other pathogens. f Modulation of the immune system. Probiotics modulate innate immunity and adaptive immunity by T and B-cell activation through the dendritic cell in the mucosa. Dendritic cell is found in the mucosal lamina propria, surface epithelium and Peyer's patches. The M-cells are highly specific epithelial cells and they take up probiotics in the Peyer’s patches. Dendritic cells supply them to the mesenteric lymph node where the T-cells and antibody-producing B-cells are produced