Project description:The opportunistic pathogen Staphylococcus aureus is carried asymptomatically by about one-third of the human population. Body sites known to be colonized by S. aureus are the skin, nasopharynx and gut. In particular, the mechanisms that allow S. aureus to pass the gut epithelial barrier and to invade the bloodstream are poorly understood. Therefore, our present study was aimed at investigating possible differences between gut-colonizing and bacteremia isolates of S. aureus. To this end, 74 gut-colonizing isolates from healthy individuals and 144 blood-culture isolates were characterized by whole-genome sequencing. Subsequently, the cellular and extracellular proteomes of six representative isolates were examined by mass spectrometry. Lastly, the virulence potential of these isolates was evaluated using infection models based on human gut epithelial cells, blood cells, and a small animal infection model. Intriguingly, our results show that gut-colonizing and bacteremia isolates with the same sequence type (ST1 or ST5) are very similar at the genomic and proteomic levels. Nonetheless, they display differences in virulence, but gut-colonizing isolates may be more virulent than bacteremia isolates and vice versa. Importantly, we show that the main decisive factor preventing infection of gut epithelial cells in vitro is the presence of a tight barrier. Based on our present observations, we propose that the integrity of the gut epithelial layer, rather than the pathogenic potential of a gut-colonizing S. aureus strain, is the main decisive factor that determines whether this colonizer will become an invasive pathogen.
Project description:The mammalian gut secretes a family of multifunctional peptides that affect appetite, intestinal secretions, and motility, while some regulate the microbiota. We report peptide YY (PYY1-36), but not endocrine PYY3-36, is an antimicrobial peptide (AMP) expressed by gut epithelial Paneth Cells (PC). PC-PYY has limited antibacterial activity, but shows selective activity against virulent hyphal, but not yeast forms, of Candida albicans. 5 PC-PYY is a cationic molecule that interacts with the anionic surfaces of fungal hyphae to cause membrane disruption and transcriptional reprogramming to maintain the yeast phenotype of the fungus. PC-PYY is packaged into secretory granules and is secreted into and retained by surface mucus, which optimizes PC-PYY activity. Hence, PC-PYY acts as a selective antifungal AMP that contributes to the maintenance of gut fungal commensalism.
Project description:The balance between tolerogenic and inflammatory responses determines immune homeostasis in the gut. Dysbiosis and a defective host defense against invading intestinal bacteria can shift this balance via bacterial-derived metabolites and trigger chronic inflammation. We show that the short chain fatty acid butyrate modulates monocyte to macrophage differentiation by promoting antimicrobial effector functions. The presence of butyrate modulates antimicrobial activity via a shift in macrophage metabolism and reduction in mTOR activity. This mechanism is furthermore dependent on the inhibitory function of butyrate on histone deacetylase 3 (HDAC3) driving transcription of a set of antimicrobial peptides including calprotectin. The increased antimicrobial activity against several bacterial species is not associated with increased production of conventional cytokines. Butyrate imprints antimicrobial activity of intestinal macrophages in vivo. Our data suggest that commensal bacteria derived butyrate stabilize gut homeostasis by promoting antimicrobial host defense pathways in monocytes that differentiate into intestinal macrophages.
Project description:Effective innate immunity against many microbial pathogens requires macrophage programs that upregulate phagocytosis and direct antimicrobial pathways, two functions generally assumed to be coordinately regulated. Here the regulation of these key functions was investigated in human blood-derived macrophages. IL-10 induced the phagocytic pathway, including CD209 and scavenger receptors, resulting in phagocytosis of mycobacteria and oxLDL. IL-15 induced the vitamin D-dependent antimicrobial pathway and CD209, yet the cells were less phagocytic. The differential regulation of macrophage functional programs was confirmed by analysis of the spectrum of leprosy lesions: the macrophage phagocytosis pathway was prominent in the clinically progressive, multibacillary form, whereas the vitamin D-dependent antimicrobial pathway predominated in the self-limited form of the disease and in patients undergoing reversal reactions from the multibacillary to the self-limited form. These data indicate that macrophage programs for phagocytosis and antimicrobial responses are distinct and differentially regulated in innate immunity in bacterial infections.