Macrophages respond to infection or injury by changing from a resting cellular phenotype to an state defined by the expression of various cytotoxic effector molecules. Regulation of the transition from a resting to an activated state is effected by cytokines and/or pathogenic signals. Thioglycolate is often used to induce peritonitis in mice to recover primary peritoneal macrophages. We thus tested survival of wild-type GBS strain NEM316 and its isogenic DpilB mutant in this cellular model mimicking in vivo situation and, again, did not found any significant differences between WT and mutant strains. Heterologous expression of pilB from NEM316 in L. lactis did not confer any significant advantage for survival in primary activated macrophages, as compared to the control strain. In conclusion, our results do not substantiate the proposal that PilB is a major player in resistance to innate immune host defenses, i.e. resistance to macrophage killing and to antimicrobial peptides. However, we cannot exclude that phenotypic differences are not due to sequence VPC-14228 variations in the PilB proteins. Besides having an immature immune system, newborn are also more permissive to infections than adult mice due to increased bacterial translocation through the epithelia of their major organs, such as intestine, lung, kidney, liver, and brain. The GBS PI-2a pilus operon was reported to promote biofilm formation, adherence to human epithelial cells and transepithelial migration, and adhesion and invasion of brain microvascular endothelial cells. These phenotypic traits may therefore strongly TM5275 sodium salt impact GBS virulence in neonate mice but not in adult mice, as observed in this study. Our results also illustrate the fact that the definition of a virulence factor primarily depends on the animal model used. Hence, GBS pilus can be considered as a virulence factor in the neonatal context. Prebiotics are nondigestible food ingredients, whose beneficial effects on the host result from the selective stimulation of growth and/or activity of members of the gut microbiota, specifically bifidobacteria and lactobacteria. Inulin, generally extracted from chicory roots, is a prebiotic formed by a chain of fructose molecules connected by b- glycosidic bonds, terminated by one glucose molecule, which is not decomposed by digestive enzymes due to its chemical structure.