Lactobacilli can belong to the gut flora or to the flora associating with gastrointestinal epithelial surfaces. They play an important role within the microbial defense mechanisms taking part in the colonization resistance and in the decontamination of the host. Lactobacilli affect the immune response. They accelerate the revival of the small intestinal epithelial cells. Those strains of lactobacilli with distinct antagonistic properties with lysozyme activity and resistance against lysozyme often develop a compact glycocalyx. They are endowed with a high adhesion capacity. The intestinal lactoflora consists of several species with different defense properties.