PubMed Health⌕ Search

Biomedical subjects

Victor Nizet

Publications and source records attributed to Victor Nizet.

At least 19 recordsLinked to original sources
PubMed2004

Invasive M1T1 group A Streptococcus undergoes a phase-shift in vivo to prevent proteolytic degradation of multiple virulence factors by SpeB.

A globally disseminated strain of M1T1 group A Streptococcus (GAS) has been associated with severe infections in humans including necrotizing fasciitis and toxic shock syndrome. Recent clinicoepidemiologic data showed a striking inverse relationship between disease severity and the degree to which M1T1 GAS express the streptococcal cysteine protease, SpeB. Electrophoretic 2-D gel analysis of the secreted M1T1 proteome, coupled with MALDI-TOF mass spectroscopy, revealed that expression of active SpeB caused the degradation of the vast majority of secreted GAS proteins, including several known virulence factors. Injection of a SpeB+/SpeA- M1T1 GAS strain into a murine subcutanous chamber model of infection selected for a stable phase-shift to a SpeB-/SpeA+ phenotype that expressed a full repertoire of secreted proteins and possessed enhanced lymphocyte-stimulating capacity. The proteome of the SpeB-in vivo phase-shift form closely matched the proteome of an isogenic speB gene deletion mutant of the original M1T1 isolate. The absence or the inactivation of SpeB allowed proteomic identification of proteins in this M1T1 clone that are not present in the previously sequenced M1 genome including SpeA and another bacteriophage-encoded novel streptodornase allele. Further proteomic analysis of the M1T1 SpeB+ and SpeB- phase-shift forms in the presence of a cysteine protease inhibitor demonstrated differences in the expression of several proteins, including the in vivo upregulation of SpeA, which occurred independently of SpeB inactivation.

Animals↗
PubMed2003

Alanylation of teichoic acids protects Staphylococcus aureus against Toll-like receptor 2-dependent host defense in a mouse tissue cage infection model.

Staphylococcus aureus is inherently resistant to cationic antimicrobial peptides because of alanylation of cell envelope teichoic acids. To test the effect of alanylated teichoic acids on virulence and host defense mediated by Toll-like receptor 2 (TLR2), wild-type (wt) S. aureus ATCC35556 (S.a.113) and its isogenic mutant expressing unalanylated teichoic acids (dlt(-)) were compared in a tissue cage infection model that used C57BL/6 wt and TLR2-deficient mice. The minimum infective doses (MID) to establish persistent infection with S.a.113 were 10(3) and 10(2) colony-forming units (cfu) in wt and TLR2(-/-) mice, respectively. The corresponding MID for dlt(-) were 5x105 and 10(3) cfu in wt and TLR2(-/-) mice, respectively. Both mouse strains showed bacterial-load-dependent inflammation with elevations in tumor necrosis factor, macrophage inflammatory protein 2, and leukocytes, with increasing proportions of dead cells. These findings indicate that alanylated teichoic acids contribute to virulence of S. aureus, and TLR2 mediates host defense, which partly targets alanylated teichoic acids.

Animals↗
PubMed2003

HIF-1alpha is essential for myeloid cell-mediated inflammation.

Granulocytes and monocytes/macrophages of the myeloid lineage are the chief cellular agents of innate immunity. Here, we have examined the inflammatory response in mice with conditional knockouts of the hypoxia responsive transcription factor HIF-1alpha, its negative regulator VHL, and a known downstream target, VEGF. We find that activation of HIF-1alpha is essential for myeloid cell infiltration and activation in vivo through a mechanism independent of VEGF. Loss of VHL leads to a large increase in acute inflammatory responses. Our results show that HIF-1alpha is essential for the regulation of glycolytic capacity in myeloid cells: when HIF-1alpha is absent, the cellular ATP pool is drastically reduced. The metabolic defect results in profound impairment of myeloid cell aggregation, motility, invasiveness, and bacterial killing. This role for HIF-1alpha demonstrates its direct regulation of survival and function in the inflammatory microenvironment.

Adenosine Triphosphate↗
PubMed2003

Selective modulation of superantigen-induced responses by streptococcal cysteine protease.

Streptococcal pyrogenic exotoxin (Spe) B, a streptococcal cysteine protease, is believed to be important in group A streptococcal (GAS) pathogenesis. The present study examined the effect of SpeB on the activity of superantigenic exotoxins secreted by M1T1 GAS isolates. The proliferative response of human lymphocytes to culture supernatant (SUP) from an SpeB(+) isolate increased significantly (P<.05) when the isolate was grown with N-[N-(L-3-trans-carboxyoxirane-2-carbonyl)-L-leucyl]-agmatine, a cysteine protease inhibitor. The lymphocyte-stimulating activity of SUP from a spontaneous SpeB(-) variant or SpeB(-) knockout (DeltaSpeB) mutant was also significantly higher than that of SUP from the SpeB(+) parent isolate (P<.001). The addition of recombinant SpeB to the DeltaSpeB mutant reduced the lymphocyte response to a level comparable to that with the SpeB(+) isolate. SpeB affected superantigens that stimulate cells expressing T cell receptor Vbeta (TCRBV)-4, TCRBV7, and TCRBV8 but not those that stimulate TCRBV2. SpeB has a selective proteolytic effect on GAS superantigens.

Bacterial Proteins↗
PubMed2003

Endogenous production of antimicrobial peptides in innate immunity and human disease.

Antimicrobial peptides are diverse and evolutionarily ancient molecules produced by all living organisms. Peptides belonging to the cathelicidin and defensin gene families exhibit an immune strategy as they defend against infection by inhibiting microbial survival, and modify hosts through triggering tissue-specific defense and repair events. A variety of processes have evolved in microbes to evade the action of antimicrobial peptides, including the ability to degrade or inactivate antimicrobial peptides, or suppress host production of the peptide in response to infection. Animal models and clinical investigations have shown that an absence of cathelicidin or defensin antimicrobials can lead to disease. In this article, we review important recent advances in understanding the biology of antimicrobial peptides and their role in normal immunity and human disease.

Antimicrobial Cationic Peptides↗
PubMed2003

Antimicrobial and protease inhibitory functions of the human cathelicidin (hCAP18/LL-37) prosequence.

Cathelicidins are a class of small cationic peptide antibiotics that are expressed in skin and in other epithelial cells and are an active component of mammalian innate immunity. Human cathelicidin (hCAP18/LL-37) consists of a conserved prosequence called the cathelin-like domain and a C-terminal peptide named LL-37. To date, our understanding of the cathelin-like domain was very limited. To bring insight into the function of this evolutionarily conserved prosequence, we produced recombinant human cathelin-like protein and full-length hCAP18/LL-37 in Escherichia coli. As the cathelin-like protein shares homology with the cystatin family of cysteine protease inhibitors, we first analyzed the effect of the cathelin-like recombinant protein on the cysteine protease cathepsin L. We found that the cathelin-like protein inhibited protease activity. Next, we tested the cathelin-like protein for antimicrobial activity using solid phase radial diffusion and liquid phase killing assays. The cathelin-like prosequence, but not full-length hCAP18/LL-37, killed human pathogens including E. coli and methicillin-resistant Staphylococcus aureus at concentrations ranging from 16 to 32 microM. Together these findings suggest that after proteolytic cleavage the cathelin-like domain can contribute to innate host defense through inhibition of bacterial growth and limitation of cysteine-proteinase-mediated tissue damage. As these dual functions are complementary to the LL-37 peptide released from the C-terminus of full-length hCAP18/LL-37, human cathelicidin represents an elegant multifunctional effector molecule for innate immune defense of the skin.

Anti-Bacterial Agents↗
PubMed2003

Cathelicidins and innate defense against invasive bacterial infection.

Cathelicidins are small cationic peptides that possess broad-spectrum antimicrobial activity. These gene-encoded 'natural antibiotics' are produced by several mammalian species on epithelial surfaces and within the granules of phagocytic cells. Since their discovery over a decade ago, cathelicidins have been speculated to function within the innate immune system, contributing to a first line of host defense against an array of microorganisms. Consequently, cathelicidins have captured the interest of basic investigators in the diverse fields of cell biology, immunology, protein chemistry and microbiology. A burgeoning body of experimental research now appears to confirm and extend the biological significance of these fascinating molecules. This article reviews the latest advances in the knowledge of cathelicidin antimicrobial peptides, with particular emphasis on their role in defense against invasive bacterial infection and associations with human disease conditions.

Animals↗
PubMed2003

Molecular genetic analysis of a group A Streptococcus operon encoding serum opacity factor and a novel fibronectin-binding protein, SfbX.

The group A Streptococcus (GAS) sof gene encodes the serum opacity factor protein, which is capable of opacifying mammalian sera and binding at least two host proteins, fibronectin and fibrinogen. The sof gene exists in approximately 50% of clinical isolates, and there is a classical association of so-called nephritogenic strains with the opacity factor-positive phenotype. In both a type emm49 strain and a type emm12 strain, the sequences upstream of the 5' end of sof and downstream of the putative terminator were determined to be nearly identical to a region in the M type 1 genome approximately 10 kb upstream of the emm1 gene. This close genetic linkage is likely reflected in the strict correlation of opacity factor phenotype with specific emm genotypes. A new fibronectin-binding protein gene, sfbX, was discovered immediately downstream of sof in emm12 and emm49 strains and in several other sof-positive strains. The sof and sfbX genes were found to be expressed on the same transcription unit, which was correlated with the putative promoter and rho-independant terminator sequences that flank these two genes. The sfbX genes from different emm types are predicted to encode approximately 650-residue surface-bound proteins sharing 89 to 92% sequence identity. SfbX residues approximately 1 to 480 are not highly similar to those of other known proteins, with the closest match being the Staphylococcus aureus coagulase protein. The remaining portions of these proteins (residues 481 to 650) contain four putative fibronectin-binding repeats highly similar to those of other streptococcal fibronectin-binding proteins and a potential LP(X)SG cell wall anchor motif. Targeted in-frame allelic-exchange mutagenesis, complementation, and heterologous-expression studies found that serum opacification is encoded by sof alone and that sfbX encodes a fibronectin-binding function. A recombinant SfbX protein was found to bind immobilized fibronectin and to partially inhibit GAS adherence to fibronectin. The sfbX gene was found to be present only in sof-positive strains, and together these genes could influence the spectrum of tissues colonized by sof-positive GAS.

Amino Acid Sequence↗
PubMed2003

Group B streptococcal beta-hemolysin/cytolysin activates neutrophil signaling pathways in brain endothelium and contributes to development of meningitis.

Meningitis occurs when blood-borne pathogens cross the blood-brain barrier (BBB) in a complex interplay between endothelial cells and microbial gene products. We sought to understand the initial response of the BBB to the human meningeal pathogen group B Streptococcus (GBS) and the organism's major virulence factors, the exopolysaccharide capsule and the beta-hemolysin/cytolysin toxin (beta-h/c). Using oligonucleotide microarrays, we found that GBS infection of human brain microvascular endothelial cells (HBMEC) induced a highly specific and coordinate set of genes including IL-8, Groalpha, Grobeta, IL-6, GM-CSF, myeloid cell leukemia sequence-1 (Mcl-1), and ICAM-1, which act to orchestrate neutrophil recruitment, activation, and enhanced survival. Most strikingly, infection with a GBS strain lacking beta-h/c resulted in a marked reduction in expression of genes involved in the immune response, while the unencapsulated strain generally induced similar or greater expression levels for the same subset of genes. Cell-free bacterial supernatants containing beta-h/c activity induced IL-8 release, identifying this toxin as a principal provocative factor for BBB activation. These findings were further substantiated in vitro and in vivo. Neutrophil migration across polar HBMEC monolayers was stimulated by GBS and its beta-h/c through a process involving IL-8 and ICAM-1. In a murine model of hematogenous meningitis, mice infected with beta-h/c mutants exhibited lower mortality and decreased brain bacterial counts compared with mice infected with the corresponding WT GBS strains.

Bacterial Proteins↗
PubMed2002

Synergistic action of nitric oxide release from murine macrophages caused by group B streptococcal cell wall and beta-hemolysin/cytolysin.

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. It has been shown that GBS beta-hemolysin/cytolysin (beta-h/c) stimulates the transcription of inducible NO synthase (iNOS) in murine macrophages via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Here, it is demonstrated that the GBS cell wall and beta-h/c act synergistically to induce iNOS in interferon (IFN)-gamma-primed [corrected] RAW 264.7 murine macrophages. In nonprimed macrophages, combined activation by the GBS cell wall plus beta-h/c is necessary to induce an NO response, which indicates that both virulence factors cooperate to substitute for the priming signal typically provided by IFN-gamma [corrected].

Animals↗
PubMed2002

Cellular activation, phagocytosis, and bactericidal activity against group B streptococcus involve parallel myeloid differentiation factor 88-dependent and independent signaling pathways.

Group B streptococci (GBS) vigorously activate inflammatory responses. We reported previously that a secreted GBS "factor" activates phagocytes via Toll-like receptor (TLR)2 and TLR6, but that GBS cell walls activate cells independently of these receptors. We hypothesized that the phagocytic immune functions in response to GBS, such as inflammation, uptake, and elimination of bacteria, occur through a coordinated engagement of TLRs, along with the coreceptors CD14 and CD11b/CD18. Using various knockout mice we show that GBS-induced activation of p38 and NF-kappaB depends upon the expression of the cytoplasmic TLR adapter protein, myeloid differentiation factor 88 (MyD88), but not TLR2 and/or TLR4. Macrophages with deletions of CD14 and complement receptor 3 had a normal cytokine response to whole bacteria, although the response to GBS factor was abrogated in CD14-null cells. The intracellular formation of bactericidal oxygen species proved to be MyD88 dependent; however, uptake of GBS, a prerequisite for intracellular killing by O(2) radicals, occurred independently of MyD88. While deletion of complement receptor 3 greatly diminished the uptake of opsonized GBS, it did not affect the formation of bactericidal O(2) radicals or inflammatory signaling intermediates. We conclude that the inflammatory, bactericidal, and phagocytic responses to GBS occur via parallel but independent processes.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Group B streptococcal beta-hemolysin induces mortality and liver injury in experimental sepsis.

New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) serotype III strain (COH1) and its isogenic nonhemolytic (NH) and hyperhemolytic (HH) mutants. Mortality differed significantly between rabbits infected with the HH mutant IN40 (67%), compared with rabbits infected with the wt COH1 strain (27%) and the NH strains COH1-20 and COH1:cylEDeltacat (13% and 0%, respectively; P<.05). Histopathologically, disseminated septic microabscesses surrounded by necrotic foci were found exclusively in the livers of HH mutant IN40-infected animals. Serum transaminase levels were 20-fold higher in the HH-infected group, compared with rabbits infected with the other strains. Positive TUNEL (in situ terminal deoxynucleotide transferase-mediated dUTP nick end labeling) staining and activation of caspase-3 in hepatocytes were more frequent in HH-infected than in wt-infected animals and absent in the NH mutant COH1-20-infected group, indicating that GBS beta-hemolysin triggers apoptotic pathways in hepatocytes. This work provides the first evidence that GBS beta-hemolysin plays a crucial role in the pathophysiology of GBS sepsis by inducing liver failure and high mortality.

Animals↗
PubMed2002

Streptolysin S and necrotising infections produced by group G streptococcus.

BACKGROUND: We encountered three patients with severe necrotising soft tissue infections due to beta-haemolytic group G streptococcus. Due to strong clinical similarities with invasive infections produced by group A streptococcus, we investigated a potential link of shared beta-haemolytic phenotype to disease pathogenesis. METHODS: Hybridisation, DNA sequencing, targeted mutagenesis, and complementation studies were used to establish the genetic basis for group G streptococcus beta-haemolytic activity. The requirement of group G streptococcus beta-haemolysin in producing necrotising infection was examined in mice. FINDINGS: Each patient had an underlying medical condition. beta-haemolytic group G streptococcus was the sole microbial isolate from debrided necrotic tissue. The group G streptococcus chromosome contained a homologue of the nine-gene group A streptococcus sag operon encoding the beta-haemolysin streptolysin S (SLS). Targeted mutagenesis of the putative SLS structural gene sagA in group G streptococcus eliminated beta-haemolytic activity. Mice injected subcutaneously with wild-type group A streptococcus or group G streptococcus developed an inflammatory lesion with high bacterial counts, marked neutrophil infiltration, and histopathological evidence of diffuse tissue necrosis. These changes were not found in mice injected with the isogenic group A streptococcus or group G streptococcus SLS-negative mutants. INTERPRETATION: In patients with underlying medical conditions, beta-haemolytic group G streptococcus can produce necrotising soft tissue infections resembling those produced by group A streptococcus. The beta-haemolytic phenotype of group G streptococcus is produced by the exotoxin SLS, encoded by a functional homologue of the nine-gene group A streptococcus sag operon. SLS expression contributes to the pathogenesis of streptococcal necrotising soft tissue infection.

Animals↗
PubMed2002

Group B streptococcal beta-hemolysin/cytolysin promotes invasion of human lung epithelial cells and the release of interleukin-8.

Pneumonia and lung injury are hallmarks of early-onset neonatal group B streptococcal (GBS) infections. Production of a beta-hemolysin/cytolysin (beta-h/c) encoded by the cylE gene is associated with GBS virulence in vivo. To elucidate the contribution of the beta-h/c toxin to lung injury, the interactions of GBS wild-type strains and isogenic cylE mutants with A549 lung epithelial cells were examined. Compared with wild-type GBS strains, cylE mutants did not produce cytolytic injury, even at high inocula, and exhibited decreased cellular invasion. Additionally, cylE mutants induced less A549 cell release of the neutrophil chemoattractant interleukin (IL)-8. GBS invasion and IL-8 induction were significantly reduced in the presence of dipalmotyl phosphatidylcholine, a major constituent of lung surfactant and a known inhibitor of beta-h/c activity. These data indicate that the GBS beta-h/c contributes to invasion and immune activation of lung epithelial cells and may represent a multifunctional virulence factor in the early pulmonary stages of GBS infection.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2002

Streptococcal beta-hemolysins: genetics and role in disease pathogenesis.

A zone of beta-hemolysis surrounding colonies on blood-agar media is a hallmark phenotypic feature of the pathogens group A Streptococcus (GAS) and group B Streptococcus (GBS). In each case, lysis of red blood cells reflects the action of a potent protein exotoxin. Although these toxins have been the subjects of numerous investigations over the years, their purification and molecular identification have proven elusive. These difficulties reflect the instability of hemolytic activity, as both toxins function only in the context of the bacterial surface or certain high molecular weight 'stabilizer' molecules. This review highlights the recent discoveries of two markedly distinct genetic loci, necessary and sufficient for the beta-hemolytic phenotypes of GAS and GBS, respectively. The generation of isogenic GAS and GBS beta-hemolysin-deficient mutants and their analysis using in vitro and in vivo model systems has shown that both toxins function as virulence factors in the pathogenesis of invasive infections.

Bacterial Proteins↗
PubMed2002

Late-onset group B streptococcal infection in identical twins: insight to disease pathogenesis.

Late-onset group B streptococcal (GBS) infection affecting identical twins is described. Although exhibiting similar signs and symptoms at presentation, twin A suffered fulminant fatal meningitis while twin B recovered completely. The GBS isolates proved to be genetically identical and possessed equivalent abilities to invade and injure cells of the human blood-brain barrier in vitro. Clinical variables associated with the adverse outcome in twin A were longer duration of fever prior to antibiotics and the development of neutropenia. The case histories and experimental data are reviewed to underscore key features of GBS disease pathogenesis.

Age of Onset↗