Group B Streptococcus GAPDH Is Released upon Cell Lysis, Associates with Bacterial Surface, and Induces Apoptosis in Murine Macrophages

Glyceraldehyde 3-phosphate dehydrogenases (GAPDH) are cytoplasmic glycolytic enzymes that, despite lacking identifiable secretion signals, have been detected at the surface of several prokaryotic and eukaryotic organisms where they exhibit non-glycolytic functions including adhesion to host components. Group B Streptococcus (GBS) is a human commensal bacterium that has the capacity to cause life-threatening meningitis and septicemia in newborns. Electron microscopy and fluorescence-activated cell sorter (FACS) analysis demonstrated the surface localization of GAPDH in GBS. By addressing the question of GAPDH export to the cell surface of GBS strain NEM316 and isogenic mutant derivatives of our collection, we found that impaired GAPDH presence in the surface and supernatant of GBS was associated with a lower level of bacterial lysis. We also found that following GBS lysis, GAPDH can associate to the surface of many living bacteria. Finally, we provide evidence for a novel function of the secreted GAPDH as an inducer of apoptosis of murine macrophages

Mycobacterium bovis Bacillus Calmette-Guerin Vaccination Mobilizes Innate Myeloid-Derived Suppressor Cells Restraining In Vivo T Cell Priming via IL-1R-Dependent Nitric Oxide Production

International audienceEarly immune response to the largely used Mycobacterium bovis bacillusCalmette-Gue´rin (BCG) intradermal vaccine remains ill defined. Three days after BCG inoculation into the mouse ear, in addition to neutrophils infiltrating skin, we observed CD11b+Ly-6CintLy-6G2 myeloid cells.Neutrophil depletionmarkedly enhanced their recruitment.These cells differed frominflammatory monocytes and required MyD88-dependent BCG-specific signals to invade skin, whereas neutrophil influx was MyD88 independent. Upon BCG phagocytosis, CD11b+Ly-6CintLy-6G2cells produced NO,which required the IL-1 receptor.DespiteNOproduction, theywere unable to killBCGor the nonpathogenicMycobacterium smegmatis.However, theymarkedly impairedTcell priming in the draining lymph node. Their elimination by all-trans retinoid acid treatment increased the number of IFN-g–producing CD4 T cells. Thus, BCG vaccination recruits innate myeloid-derived suppressor cells, akin to mouse tumor-infiltrating cells. These propathogenic cells dampen the early T cell response and might facilitate BCG persistence

Role of the group B antigen of Streptococcus agalactiae a peptidoglycan-anchored polysaccharide involved in cell wall biogenesis: a Peptidoglycan-Anchored Polysaccharide involved in cell wall biogenesis

Streptococcus agalactiae (Group B streptococcus, GBS) is a leading cause of infections in neonates and an emerging pathogen in adults. The Lancefield Group B carbohydrate (GBC) is a peptidoglycan-anchored antigen that defines this species as a Group B Streptococcus. Despite earlier immunological and biochemical characterizations, the function of this abundant glycopolymer has never been addressed experimentally. Here, we inactivated the gene gbcO encoding a putative UDP-N-acetylglucosamine-1-phosphate:lipi​dphosphate transferase thought to catalyze the first step of GBC synthesis. Indeed, the gbcO mutant was unable to synthesize the GBC polymer, and displayed an important growth defect in vitro. Electron microscopy study of the GBC-depleted strain of S. agalactiae revealed a series of growth-related abnormalities: random placement of septa, defective cell division and separation processes, and aberrant cell morphology. Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus. Finally, the subcellular localization of the PG hydrolase PcsB, which has a critical role in cell division of streptococci, was altered in the gbcO mutant. Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis. Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta –hemolytic streptococci

Role of the Serine-Rich Surface Glycoprotein Srr1 of Streptococcus agalactiae in the Pathogenesis of Infective Endocarditis

The binding of bacteria to fibrinogen and platelets are important events in the pathogenesis of infective endocarditis. Srr1 is a serine-rich repeat glycoprotein of Streptococcus agalactiae that binds directly to the Aα chain of human fibrinogen. To assess the impact of Srr1 on the pathogenesis of endocarditis due to S. agalactiae, we first examined the binding of this organism to immobilized human platelets. Strains expressing Srr1 had significantly higher levels of binding to human platelets in vitro, as compared with isogenic Δsrr1 mutants. In addition, platelet binding was inhibited by pretreatment with anti-fibrinogen IgG or purified Srr1 binding region. To assess the contribution of Srr1 to pathogenicity, we compared the relative virulence of S. agalactiae NCTC 10/84 strain and its Δsrr1 mutant in a rat model of endocarditis, where animals were co-infected with the WT and the mutant strains at a 1∶1 ratio. At 72 h post-infection, bacterial densities (CFU/g) of the WT strain within vegetations, kidneys, and spleens were significantly higher, as compared with the Δsrr1 mutant. These results indicate that Srr1 contributes to the pathogenesis of endocarditis due to S. agalactiae, at least in part through its role in fibrinogen-mediated platelet binding