Mode Process Mechanism Examples Barrier Function Decreased apoptosis of epithelial cells Decreased TNF-α production Lactobacillus rhamnosus GG Increasing mucin production Increased expression of MUC 2 Lactobacillus sp Host cell Antimicrobial Peptides Defensins (hBD protein) Increased up regulation of Defensin E coli strain DSM 17252S2 Cathelcidins By butyrate production   Probiotic Antimicrobial Factors Lowering the luminal pH By secretion of SCFA’s Most of the probiotics bacteria Bacteriocin production By Gram positive probiotics Microcin production By Gram negative probiotics Epithelial Adherence By competing with pathogens Directly or indirectly by producing protein that block adherence   Immune Modulation Blocking pro Inflammatory molecules By attenuating IL-8 secretion or blocking the degradation of the counter-regulatory factor IκB Salmonella tyhimurium VSL#3 probiotics Increasing mucosal immunity Increasing IgA Production L. casei Interference with Quorum Sensing Signaling Blocks the communication between pathogenic bacteria By secreting molecules which blocks quorum sensing signaling L. acidophilus

Table 1: Various mechanisms of probiotics action on human intestine cells. Abbreviations: TNF-α: Tumor necrosis factor alpha; MUC 2: Mucin 2, hBD: Hemoglobin subunit delta; SCFA: Short chain fatty acids; IL-8: Interleukin 8; and IκB: Inhibitor of kappa B.