| 1. |
- Barkman, Cecilia, 1962, et al.
(författare)
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Soluble bacterial constituents down-regulate secretion of IL-12 in response to intact Gram-positive bacteria.
- 2008
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Ingår i: Microbes and infection / Institut Pasteur. - : Elsevier BV. - 1286-4579. ; 10:14-15, s. 1484-93
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Tidskriftsartikel (refereegranskat)abstract
- Intact Gram-positive bacteria induce production of large amounts of IL-12 from freshly isolated human monocytes. Here the bacterial structures and signalling pathways involved were studied and compared with those leading to IL-6 production, and to IL-12 production in response to LPS after IFN-gamma pre-treatment. Intact bifidobacteria induced massive production of IL-12 (1ng/ml) and IL-6 (>30ng/ml) from human PBMC, whereas fragmented bifidobacteria induced IL-6, but no IL-12. IL-12 production induced by intact bifidobacteria was inhibited by pre-treatment with bifidobacterial sonicate, peptidoglycan, muramyl dipeptide, lipoteichoic acid, the soluble TLR2 agonist Pam(3)Cys-SK(4), or anti-TLR2 antibodies. Blocking of phagocytosis by cytochalasin, inhibition of the JNK or NF-kappaB pathways or treatment with Wortmannin also reduced the IL-12 response to intact Gram-positive bacteria. LPS induced moderate levels of IL-12 (0.31ng/ml), but only from IFN-gamma pre-treated PBMC. This IL-12 production was enhanced by Wortmannin and unaffected by blocking the JNK pathway. Thus, intact Gram-positive bacteria trigger monocyte production of large amounts of IL-12 via a distinct pathway that is turned off by fragmented Gram-positive bacteria. This may be a physiological feedback, since such fragments may signal that further activation of the phagocyte via the IL-12/IFN-gamma loop is unnecessary.
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| 2. |
- Karami, Nahid, 1959, et al.
(författare)
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Transfer of an ampicillin resistance gene between two Escherichia coli strains in the bowel microbiota of an infant treated with antibiotics
- 2007
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press (OUP). - 0305-7453 .- 1460-2091. ; 60:5, s. 1142-1145
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Tidskriftsartikel (refereegranskat)abstract
- Objectives To investigate the presumed acquisition of ampicillin resistance by an Escherichia coli strain residing in the gut of an infant. Methods E. coli strains were quantified in faecal samples obtained at regular intervals from an infant followed from birth to 12 months of age and their resistance profiles were determined. beta-Lactamases were identified by isoelectric focusing and genes by PCR followed by DNA sequencing. Plasmids were characterized by restriction fragment analysis and Southern-blot hybridization, and tested for conjugative transfer. Results The infant carried two E. coli strains, termed 29A and 29B, simultaneously in the microbiota during the first month of life. All isolates of 29A were resistant to ampicillin, whereas strain 29B, which was initially ampicillin susceptible, acquired resistance following treatment of the infant with ampicillin/amoxicillin because of urinary tract infection. Acquisition of resistance by strain 29B was associated with acquisition of a bla(TEM-1b)-encoding plasmid, pNK29, which was also present in strain 29A. Transfer of plasmid pNK29 could be replicated by conjugation from strain 29A to strain 29B in vitro. Strain 29A also adapted to ampicillin treatment by mutation of the bla(TEM-1b) promoter gene to yield a higher level of resistance. Conclusions This is an unequivocal demonstration of gene transfer between two strains co-residing in the human gut, as the donor, recipient and transconjugant strains were isolated. The results suggest the dynamic adaptation by commensal bacteria in response to antibiotic treatment may occur readily.
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| 3. |
- Martner, Anna, 1979, et al.
(författare)
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Pneumolysin released during Streptococcus pneumoniae autolysis is a potent activator of intracellular oxygen radical production in neutrophils
- 2008
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Ingår i: Infection and Immunity. - 1098-5522. ; 76:9, s. 4079-87
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae is a major cause of otitis media, pneumonia, meningitis, and septicemia in humans. The host defense against this pathogen largely depends on bacterial killing by neutrophils. A peculiar property of pneumococci is their tendency to undergo autolysis, i.e., autoinduced disruption of the bacterial cell wall mediated by activation of the enzyme LytA, under stationary growth conditions. LytA is a virulence factor, but the molecular background for this has not been fully clarified. Here we examine how bacterial compounds released upon autolysis affect the production of reactive oxygen species (ROS) in neutrophils. We found that the S. pneumoniae strains A17 and D39 induced activation of the NADPH oxidase and the production of ROS in human neutrophils and that this activation was blocked when LytA was inactivated. The ROS-inducing bacterial substance released from autolyzed bacteria was identified as the cytoplasmic toxin pneumolysin. Further screening of clinical pneumococcal strains of various sero- and genotypes revealed that selected strains expressing toxins with reduced pneumolysin-dependent hemolytic activity had decreased abilities to induce ROS in neutrophils. Furthermore, a mutated form of purified pneumolysin lacking hemolytic and complement binding functions (PdT) did not induce any oxygen radical production. The ROS produced in response to pneumolysin formed mainly intracellularly, which may explain why this production was not detected previously. ROS released intracellularly may function as signaling molecules, modifying the function of neutrophils in bacterial defense.
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| 4. |
- Martner, Anna, 1979
(författare)
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Regulation of innate and adaptive immune responses by Gram-positive and Gram-negative bacteria
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bacteria are classified as Gram-positive or Gram-negative, depending on their cell wall structure. The role of the bacterial cell wall in immune regulation is the focus of the current work. Most Gram-positive bacteria stimulate monocytes to produce large amounts of IL-12. IL-12 induces production of IFN-γ in T cells and NK cells, which, in turn, activates the bactericidal capacity of the phagocyte in synergy/concert with TNF, produced by macrophages. We studied the bacterial structures and signalling pathways involved in IL-12 production in response to intact Gram-positive bacteria. This production depended on phagocytosis and activation of the JNK, NF-κB and PI3K pathways. Gram-positive bacterial fragments inhibited IL-12 production, which may serve as a negative feedback to turn off phagocyte activation when the bacteria have been destroyed. S. pneumoniae is a Gram-positive pathogen with a peculiar habit to disintegrate in stationary culture, due to activation of autolytic enzymes that degrade the cell wall. We demonstrated that pneumococci undergoing autolysis generate bacterial fragments that shut off monocyte production of TNF, IFN-γ and IL-12, thereby counteracting phagocyte activation. Further, the cytoplasmic pneumococcal toxin pneumolysin that was released upon autolysis dramatically augmented radical oxygen production in human neutrophils. Notably, ROS were foremost produced into intracellular compartments, probably affecting neutrophil function. We also studied differences in how Gram-positive and Gram-negative bacteria modulate presentation of a model antigen to naïve T cells. Different subsets of mouse antigen-presenting cells were fed soluble ovalbumin (OVA), or OVA produced inside transgenic Gram-positive (lactobacilli/lactococci) or Gram-negative (E. coli) bacteria. Proliferation and cytokine production by OVA-specific transgenic T cells (DO11.10) was used as read-out system. “Bacterial” OVA much more efficiently activated OVA-specific CD4+ T cells, than did soluble OVA. Further, E. coli-OVA induced a greater T cell proliferation than did OVA expressed by Gram-positive bacteria. Splenic APCs pulsed with soluble OVA induced IL-13 production, while E. coli-OVA induced both IFN-γ and IL-13 and lactobacilli-OVA induced a weak IFN-γ response in the T cell culture. We also noted that peritoneal DCs induced a different T cell polarisation pattern compared to splenic DCs, supporting production of more IL-17 and IL-10, but less IL-13. Furthermore, the presence of peritoneal macrophages inhibited CD4+ T cell activation to bacterial, but not to soluble, antigens.
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| 5. |
- Martner, Anna, 1979, et al.
(författare)
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Streptococcus pneumoniae autolysis prevents phagocytosis and production of phagocyte-activating cytokines.
- 2009
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Ingår i: Infection and immunity. - 1098-5522. ; 77:9, s. 3826-37
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae is a major pathogen in humans. The pathogenicity of this organism is related to its many virulence factors, the most important of which is the thick pneumococcal capsule that minimizes phagocytosis. Another virulence-associated trait is the tendency of this bacterium to undergo autolysis in stationary phase through activation of the cell wall-bound amidase LytA, which breaks down peptidoglycan. The exact function of autolysis in pneumococcal pathogenesis is, however, unclear. Here, we show the selective and specific inefficiency of wild-type S. pneumoniae for inducing production of phagocyte-activating cytokines in human peripheral blood mononuclear cells (PBMC). Indeed, clinical pneumococcal strains induced production of 30-fold less tumor necrosis factor (TNF), 15-fold less gamma interferon (IFN-gamma), and only negligible amounts of interleukin-12 (IL-12) compared with other closely related Streptococcus species, whereas the levels of induction of IL-6, IL-8, and IL-10 production were similar. If pneumococcal LytA was inactivated by mutation or by culture in a medium containing excess choline, the pneumococci induced production of significantly more TNF, IFN-gamma, and IL-12 in PBMC, whereas the production of IL-6, IL-8, and IL-10 was unaffected. Further, adding autolyzed pneumococci to intact bacteria inhibited production of TNF, IFN-gamma, and IL-12 in a dose-dependent manner but did not inhibit production of IL-6, IL-8, and IL-10 in response to the intact bacteria. Fragments from autolyzed bacteria inhibited phagocytosis of intact bacteria and reduced the in vitro elimination of pneumococci from human blood. Our results suggest that fragments generated by autolysis of bacteria with reduced viability interfere with phagocyte-mediated elimination of live pneumococci.
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