bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mutual Enhancement of Virulence by Enterotoxigenic and Enteropathogenic
Escherichia coli
Authors: Crane John K. , Choudhari Shilpa S. , Naeher Tonniele M. , Duffey Michael E. 
Published: February 2006

ABSTRACT

Enterotoxigenic
Escherichia coli
(ETEC) and enteropathogenic
E. coli
(EPEC) are common causes of diarrhea in children in developing countries. Dual infections with both pathogens have been noted fairly frequently in studies of diarrhea around the world. In previous laboratory work, we noted that cholera toxin and forskolin markedly potentiated EPEC-induced ATP release from the host cell, and this potentiated release was found to be mediated by the cystic fibrosis transmembrane conductance regulator. In this study, we examined whether the ETEC heat-labile toxin (LT) or the heat-stable toxin (STa, also known as ST) potentiated EPEC-induced ATP release. We found that crude ETEC culture filtrates, as well as purified ETEC toxins, did potentiate EPEC-induced ATP release in cultured T84 cells. Coinfection of T84 cells with live ETEC plus EPEC bacteria also resulted in enhanced ATP release compared to EPEC alone. In Ussing chamber studies of chloride secretion, adenine nucleotides released from the host by EPEC also significantly enhanced the chloride secretory responses that were triggered by crude ETEC filtrates, purified STa, and the peptide hormone guanylin. In addition, adenosine and LT had additive or synergistic effects in inducing vacuole formation in T84 cells. Therefore, ETEC toxins and EPEC-induced damage to the host cell both enhance the virulence of the other type of
E. coli
. Our in vitro data demonstrate a molecular basis for a microbial interaction, which could result in increased severity of disease in vivo in individuals who are coinfected with ETEC and EPEC.
Molecular Characterization of Serine-, Alanine-, and Proline-Rich Proteins of
Trypanosoma cruzi
and Their Possible Role in Host Cell Infection
Authors: Baida Renata C. P. , Santos Márcia R. M. , Carmo Mirian S. , Yoshida Nobuko , Ferreira Danielle , Ferreira Alice Teixeira , El Sayed Najib M. , Andersson Bjorn , da Silveira José Franco 
Published: February 2006

ABSTRACT

We previously reported the isolation of a novel protein gene family, termed SAP (serine-, alanine-, and proline-rich protein), from
Trypanosoma cruzi
. Aided by the availability of the completed genome sequence of
T. cruzi
, we have now identified 39 full-length sequences of SAP, six pseudogenes and four partial genes. SAPs share a central domain of about 55 amino acids and can be divided into four groups based on their amino (N)- and carboxy (C)-terminal sequences. Some SAPs have conserved N- and C-terminal domains encoding a signal peptide and a glycosylphosphatidylinositol anchor addition site, respectively. Analysis of the expression of SAPs in metacyclic trypomastigotes by two-dimensional electrophoresis and immunoblotting revealed that they are likely to be posttranslationally modified in vivo. We have also demonstrated that some SAPs are shed into the extracellular medium. The recombinant SAP exhibited an adhesive capacity toward mammalian cells, where binding was dose dependent and saturable, indicating a possible ligand-receptor interaction. SAP triggered the host cell Ca
2+
response required for parasite internalization. A cell invasion assay performed in the presence of SAP showed inhibition of internalization of the metacyclic forms of the CL strain. Taken together, these results show that SAP is involved in the invasion of mammalian cells by metacyclic trypomastigotes, and they confirm the hypothesis that infective trypomastigotes exploit an arsenal of surface glycoproteins and shed proteins to induce signaling events required for their internalization.
Antigen-Responsive CD4+T Cells from C3H Mice Chronically Infected withLeishmania amazonensisAre Impaired in the Transition to an Effector Phenotype
Authors: Ramer Amanda E. , Vanloubbeeck Yannick F. , Jones Douglas E. 
Published: February 2006

ABSTRACTC3HeB/FeJ mice challenged withLeishmania majordevelop a polarized Th1 response and subsequently heal, whereasLeishmania amazonensischallenge leads to chronic lesions with high parasite loads at 10 weeks postinfection. In this study, a comparison of draining lymph node cells fromL. amazonensis- andL. major-infected mice at 10 weeks postinfection showed equivalent percentages of effector/memory phenotype CD44hiCD4+T cells producing interleukin-2 (IL-2) and proliferating after antigen stimulation. However, these cells isolated fromL. amazonensis-infected mice were not skewed toward either a Th1 or Th2 phenotype in vivo, as evidenced by their unbiased Th1/Th2 transcription factor mRNA profile. In vivo antigen stimulation with added IL-12 failed to enhance gamma interferon (IFN-γ) production of CD4+T cells fromL. amazonensis-infected mice. Antigen stimulation of CD4+T cells fromL. amazonensis-infected mice in vitro in the presence of IL-12 resulted in production of only 10 to 15% of the IFN-γ produced by T cells fromL. major-infected mice under identical conditions. These results suggest that the CD4+T-cell response during chronicL. amazonensisinfection is limited during the transition from an early activated CD4+T-cell population to an effector cell population and demonstrate that these T cells have an intrinsic defect beyond the presence or absence of IL-12 during antigen stimulation.
The Frequency ofChlamydia trachomatisMajor Outer Membrane Protein-Specific CD8+T Lymphocytes in Active Trachoma Is Associated with Current Ocular Infection
Authors: Holland Martin J. , Faal Nkoyo , Sarr Isatou , Joof Hassan , Laye Mass , Cameron Ewen , Pemberton-Pigott Frederick , Dockrell Hazel M. , Bailey Robin L. , Mabey David C. W. 
Published: February 2006

ABSTRACTChlamydia-specific cytotoxic T lymphocytes are able to control model infections but may be implicated in disease pathogenesis. HLA-A2 peptide tetramers toChlamydia trachomatismajor outer membrane protein 258-266 (MOMP258-266) and MOMP260-268 were used to characterize HLA class I-restricted CD8+T cells in Gambian children aged 4 to 15 years with clinical signs of active trachoma and/or infection withC. trachomatis. The frequencies of circulating HLA-A2 tetramer binding cells (TBC) were determined in whole blood samples by flow cytometric analysis. Initial screening of subjects with an anti-HLA-A2 antibody confirmed the presence of either HLA-A2 or HLA-A28. These were subsequently further divided by molecular subtyping. TheC. trachomatis-specific HLA-A2 peptide tetramers were able to bind T cells with receptors from subjects which were restricted by either the HLA-A2 or the HLA-A28 restriction element. In this population, the median value ofC. trachomatis-specific CD8+T cells was 0.02%, with frequencies of up to 3.71% of CD8+T cells reactive with a single tetramer in a minority of subjects. TBC were detected more often in subjects who were infected at the ocular surface, and their presence was associated with infection episodes of longer duration. Detection ofC. trachomatis-specific TBC was not associated with the presence of disease or with the estimated load of ocularC. trachomatisinfection at the time of sample collection. High frequencies ofC. trachomatis-specific cells did not predict subsequent appearance or resolution of the clinical disease signs of active trachoma.
CD40 Restrains In Vivo Growth ofToxoplasma gondiiIndependently of Gamma Interferon
Authors: Subauste Carlos S. , Wessendarp Matthew 
Published: February 2006

ABSTRACTCD40-CD154 interaction is pivotal for resistance against numerous pathogens. However, it is not known if this pathway can also enhance in vivo resistance in gamma interferon (IFN-γ)-deficient hosts. This is an important question because patients and mice with defects in type 1 cytokine response can control a variety of pathogens. While blockade of endogenous CD154 resulted in a remarkable increase in parasite load in IFN-γ−/−mice infected withToxoplasma gondii, in vivo administration of a stimulatory anti-CD40 monoclonal antibody markedly reduced parasite load. This latter effect took place even in T-cell-depleted mice and was accompanied by induction of macrophage toxoplasmacidal activity. CD40 stimulation restrictedT. gondiireplication independently of STAT1, p47 GTPases, and nitric oxide. In vivo CD40 ligation enhanced tumor necrosis factor alpha (TNF-α) production byT. gondii-infected macrophages. In addition, CD40 stimulation required the presence of TNF receptor 2 to reduce parasite load in vivo. These results suggest that CD40-CD154 interaction regulates IFN-γ-independent mechanisms of host protection through induction of macrophage antimicrobial activity and modulation of TNF-α signaling.
Biofilm Formation by
Moraxella catarrhalis
In Vitro: Roles of the UspA1 Adhesin and the Hag Hemagglutinin
Authors: Pearson Melanie M. , Laurence Cassie A. , Guinn Sarah E. , Hansen Eric J. 
Published: February 2006

ABSTRACT

Mutant analysis was used to identify
Moraxella catarrhalis
gene products necessary for biofilm development in a crystal violet-based assay involving 24-well tissue culture plates. The wild-type
M. catarrhalis
strains that formed the most extensive biofilms in this system proved to be refractory to transposon mutagenesis, so an
M. catarrhalis
strain was constructed that was both able to form biofilms in vitro and amenable to transposon mutagenesis. Chromosomal DNA from the biofilm-positive strain O46E was used to transform the biofilm-negative strain O35E; transformants able to form biofilms were identified and subjected to transposon-mediated mutagenesis. Biofilm-negative mutants of these transformants were shown to have a transposon insertion in the
uspA1
gene. Nucleotide sequence analysis revealed that the biofilm-positive transformant T14 contained a hybrid O46E-O35E
uspA1
gene, with the N-terminal 155 amino acids being derived from the O46E UspA1 protein. Transformant T14 was also shown to be unable to express the Hag protein, which normally extends from the surface of the
M. catarrhalis
cell. Introduction of a wild-type O35E
hag
gene into T14 eliminated its ability to form a biofilm. When the hybrid O46E-O35E
uspA1
gene from T14 was used to replace the
uspA1
gene of O35E, this transformant strain did not form a biofilm. However, inactivation of the
hag
gene did allow biofilm formation by strain O35E expressing the hybrid O46E-O35E
uspA1
gene product. The Hag protein was shown to have an inhibitory or negative effect on biofilm formation by these
M. catarrhalis
strains in the crystal violet-based assay.
Binding of Vitronectin by theMoraxella catarrhalisUspA2 Protein Interferes with Late Stages of the Complement Cascade
Authors: Attia Ahmed S. , Ram Sanjay , Rice Peter A. , Hansen Eric J. 
Published: February 2006

ABSTRACTManyMoraxella catarrhalisstrains are resistant to the bactericidal activity of normal human serum (NHS). The UspA2 protein of the serum-resistant strain O35E has previously been shown to be directly involved in conferring serum resistance on this strain. Testing of 11 additional serum-resistantM. catarrhaliswild-type isolates and theiruspA1anduspA2mutants showed that theuspA1mutants of all 11 strains were consistently serum resistant and that theuspA2mutants of these same 11 strains were always serum sensitive. Analysis of complement deposition on four different serum-resistantM. catarrhalisstrains and their serum-sensitiveuspA2mutants showed that, for three of these four strain sets, the wild-type and mutant strains bound similar amounts of early complement components. In contrast, there was a significant reduction in the amount of the polymerized C9 on the wild-type strains relative to that on theuspA2mutants. These same three wild-type strains bound more vitronectin than did theiruspA2mutants. UspA2 proteins from these three strains, when expressed inHaemophilus influenzae, bound vitronectin and conferred serum resistance on this organism. Furthermore, vitronectin-depleted NHS exhibited bactericidal activity against these same three serum-resistant wild-type strains; addition of purified vitronectin to this serum restored serum resistance. In contrast, binding of the complement regulator C4b-binding protein by theM. catarrhalisstrains used in this study was found to be highly variable and did not appear to correlate with the serum-resistant phenotype. These results indicate that binding of vitronectin by UspA2 is involved in the serum resistance ofM. catarrhalis; this represents the first example of vitronectin-mediated serum resistance on a microbe.
Multilevel Control of Competence Development and Stress Tolerance in
Streptococcus mutans
UA159
Authors: Ahn Sang-Joon , Wen Zezhang T. , Burne Robert A. 
Published: February 2006

ABSTRACT

Genetic competence appears to be important in establishment of biofilms and tolerance of environmental insults. We report here that the development of competence is controlled at multiple levels in a complex network that includes two signal-transducing two-component systems (TCS). Using
Streptococcus mutans
strain UA159, we demonstrate that the histidine kinase CiaH, but not the response regulator CiaR, causes a dramatic decrease in biofilm formation and in transformation efficiency. Inactivation of
comE
or
comD
had no effect on stress tolerance, but transformability of the mutants was poor and was not restored by addition of competence-stimulating peptide (CSP). Horse serum (HS) or bovine serum albumin (BSA) had no impact on transformability of any strains. Interestingly, though, the presence of HS or BSA in combination with CSP was required for efficient induction of
comD
,
comX
, and
comYA
, and induction was dependent on ComDE and CiaH, but not CiaR. Inactivation of
comC
, encoding CSP, had no impact on transformation, and CiaH was shown to be required for optimal
comC
expression. This study reveals that
S. mutans
integrates multiple environmental signals through CiaHR and ComDE to coordinate induction of
com
genes and that CiaH can exert its influence through CiaR and as-yet-unidentified regulators. The results highlight critical differences in the role and regulation of CiaRH and
com
genes in different
S. mutans
isolates and between
S. mutans
and
Streptococcus pneumoniae
, indicating that substantial divergence in the role and regulation of TCS and competence genes has occurred in streptococci.
Silencing of the Laminin γ-1 Gene Blocks
Trypanosoma cruzi
Infection
Authors: Nde Pius N. , Simmons Kaneatra J. , Kleshchenko Yuliya Y. , Pratap Siddharth , Lima Maria F. , Villalta Fernando 
Published: February 2006

ABSTRACT

It is thought that
Trypanosoma cruzi
, the protozoan that causes Chagas' disease, modulates the extracellular matrix network to facilitate infection of human cells. However, direct evidence to document this phenomenon is lacking. Here we show that the
T. cruzi
gp83 ligand, a cell surface
trans
-sialidase-like molecule that the parasite uses to attach to host cells, increases the level of laminin γ-1 transcript and its expression in mammalian cells, leading to an increase in cellular infection. Stable RNA interference (RNAi) with host cell laminin γ-1 knocks down the levels of laminin γ-1 transcript and protein expression in mammalian cells, causing a dramatic reduction in cellular infection by
T. cruzi
. Thus, host laminin γ-1, which is regulated by the parasite, plays a crucial role in the early process of infection. This is the first report showing that knocking down the expression of a human gene by RNAi inhibits the infection of an intracellular parasite.
Salmonella enterica
Highly Expressed Genes Are Disease Specific
Authors: Rollenhagen Claudia , Bumann Dirk 
Published: February 2006

ABSTRACT

During in vitro broth culture, bacterial gene expression is typically dominated by highly expressed factors involved in protein biosynthesis, maturation, and folding, but it is unclear if this also applies to conditions in natural environments. Here, we used a promoter trap strategy with an unstable green fluorescent protein reporter that can be detected in infected mouse tissues to identify 21
Salmonella enterica
promoters with high levels of activity in a mouse enteritis model. We then measured the activities of these and 31 previously identified
Salmonella
promoters in both the enteritis and a murine typhoid fever model. Surprisingly, the data reveal that instead of protein biosynthesis genes, disease-specific genes such as
Salmonella
pathogenicity island 1 (SPI-1)-associated genes and genes involved in anaerobic respiration (enteritis) or SPI-2-associated genes and genes of the PhoP regulon (typhoid fever), respectively, dominate
Salmonella
in vivo gene expression. The overall functional profile of highly expressed genes suggests a marked shift in major transcriptional activities to nutrient utilization during enteritis or to fighting against the host during typhoid fever. The large proportion of known and novel essential virulence factors among the identified genes suggests that high expression levels during infection may correlate with functional relevance.
Quorum Quenching by anN-Acyl-Homoserine Lactone Acylase fromPseudomonas aeruginosaPAO1
Authors: Sio Charles F. , Otten Linda G. , Cool Robbert H. , Diggle Stephen P. , Braun Peter G. , Bos Rein , Daykin Mavis , Cámara Miguel , Williams Paul , Quax Wim J. 
Published: February 2006

ABSTRACTThe virulence of the opportunistic human pathogenPseudomonas aeruginosaPAO1 is controlled by anN-acyl-homoserine lactone (AHL)-dependent quorum-sensing system. During functional analysis of putative acylase genes in theP. aeruginosaPAO1 genome, the PA2385 gene was found to encode an acylase that removes the fatty acid side chain from the homoserine lactone (HSL) nucleus of AHL-dependent quorum-sensing signal molecules. Analysis showed that the posttranslational processing of the acylase and the hydrolysis reaction type are similar to those of the beta-lactam acylases, strongly suggesting that the PA2385 protein is a member of theN-terminal nucleophile hydrolase superfamily. In a bioassay, the purified acylase was shown to degrade AHLs with side chains ranging in length from 11 to 14 carbons at physiologically relevant low concentrations. The substituent at the 3′ position of the side chain did not affect activity, indicating broad-range AHL quorum-quenching activity. Of the two main AHL signal molecules ofP. aeruginosaPAO1,N-butanoyl-l-homoserine lactone (C4-HSL) andN-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C12-HSL), only 3-oxo-C12-HSL is degraded by the enzyme. Addition of the purified protein toP. aeruginosaPAO1 cultures completely inhibited accumulation of 3-oxo-C12-HSL and production of the signal molecule 2-heptyl-3-hydroxy-4(1H)-quinolone and reduced production of the virulence factors elastase and pyocyanin. Similar results were obtained when the PA2385 gene was overexpressed inP. aeruginosa. These results demonstrate that the protein has in situ quorum-quenching activity. The quorum-quenching AHL acylase may enableP. aeruginosaPAO1 to modulate its own quorum-sensing-dependent pathogenic potential and, moreover, offers possibilities for novel antipseudomonal therapies.
Protection against HeterologousBurkholderia pseudomalleiStrains by Dendritic Cell Immunization
Authors: Elvin Stephen J. , Healey Gareth D. , Westwood Angie , Knight Stella C. , Eyles James E. , Williamson E. Diane 
Published: February 2006

ABSTRACTBurkholderia pseudomallei, the causative agent of melioidosis, is a gram-negative bacterium which can cause either chronic infections or acute lethal sepsis in infected individuals. The disease is endemic in Southeast Asia and northern Australia, but little is known about the mechanisms of protective immunity to the bacterium. In this study, we have developed a procedure to utilize dendritic cells in combination with CpG oligodeoxynucleotides as a vaccine delivery vector to induce protective immune responses to various strains ofB. pseudomallei. Our results show that strong cell-mediated immune responses were generated, while antibody responses, although low, were detectable. Upon virulent challenge withB. pseudomalleistrain K96243, NCTC 4845, or 576, animals immunized with dendritic cells that were pulsed with heat-killed K96243 and matured in the presence of CpG 1826 showed significant levels of protection. These results show that a vaccine strategy that actively targets dendritic cells can evoke protective immune responses.
Endoproteolytic Processing of RhoA by Rce1 Is Required for the Cleavage of RhoA by
Yersinia enterocolitica
Outer Protein T
Authors: Fueller Florian , Bergo Martin O. , Young Stephen G. , Aktories Klaus , Schmidt Gudula 
Published: February 2006

ABSTRACT

The bacterial toxin
Yersinia
outer protein T (YopT) is a cysteine protease that cleaves Rho GTPases immediately upstream of a carboxyl-terminal isoprenylcysteine. By clipping off the lipid anchor, YopT releases Rho GTPases from membranes, resulting in rounding up of mammalian cells in culture. The proteolytic activity of YopT depends on the isoprenylation of the cysteine within the carboxyl-terminal CaaX motif, a reaction carried out by geranylgeranyltransferase type I. The CaaX motif (where “a” indicates aliphatic amino acids) of Rho proteins undergoes two additional processing steps: endoproteolytic removal of the last three amino acids (i.e., -aaX) by Rce1 (Ras-converting enzyme 1) and methylation of the geranylgeranylcysteine by Icmt (isoprenylcysteine carboxyl methyltransferase). In in vitro experiments, RhoA retaining -aaX cannot be cleaved by YopT. Nothing is known, however, about the influence of Rce1-mediated removal of -aaX on the activity of YopT in living cells. We hypothesized that Rce1-deficient mouse fibroblasts, in which the geranylgeranylated Rho proteins are not endoproteolytically processed, would be resistant to YopT. Indeed, this was the case. Microinjection of recombinant YopT into Rce1-deficient fibroblasts had no impact on the subcellular localization of RhoA and no impact on cell morphology. To determine if carboxyl methylation is also required for YopT action, we microinjected YopT into
Icmt
-deficient fibroblasts. In contrast to the results with
Rce1
-deficient cells, YopT cleaved RhoA and caused rounding up of the
Icmt
-deficient cells. Our data demonstrate that
Rce1
-mediated removal of -aaX from isoprenylated Rho GTPases is required for the proteolytic activity of YopT in living cells, whereas carboxyl methylation by Icmt is not.