bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polysaccharide Biosynthesis Locus Required for Virulence ofBacteroides fragilis
Authors: Coyne Michael J. , Tzianabos Arthur O. , Mallory Benjamin C. , Carey Vincent J. , Kasper Dennis L. , Comstock Laurie E. 
Published: July 2002

ABSTRACTBacteroides fragilis,though only a minor component of the human intestinal commensal flora, is the anaerobe most frequently isolated from intra-abdominal abscesses.B. fragilis9343 expresses at least three capsular polysaccharides—polysaccharide A (PS A), PS B, and PS C. Purified PS A and PS B have been tested in animal models and are both able to induce the formation of intra-abdominal abscesses. Mutants unable to synthesize PS B or PS C still facilitate abscess formation at levels comparable to those of wild-type 9343. To determine the contribution of PS A to abscess formation in the context of the intact organism, the PS A biosynthesis region was cloned, sequenced, and deleted from 9343 to produce a PS A-negative mutant. Animal experiments demonstrate that the abscess-inducing capability of 9343 is severely attenuated when the organism cannot synthesize PS A, despite continued synthesis of the other capsular polysaccharides. The PS A of 9343 contains an unusual free amino sugar that is essential for abscess formation by this polymer. PCR analysis of the PS A biosynthesis loci of 50B. fragilisisolates indicates that regions flanking each side of this locus are conserved in all strains. The downstream conserved region includes two terminal PS A biosynthesis genes that homology-based analyses predict are involved in the synthesis and transfer of the free amino sugar of PS A. Conservation of these genes suggests that this sugar is present in the PS A of all serotypes and may explain the abscessogenic nature ofB. fragilis.
Neutrophil Depletion duringToxoplasma gondiiInfection Leads to Impaired Immunity and Lethal Systemic Pathology
Authors: Bliss Susan K. , Gavrilescu L. Cristina , Alcaraz Ana , Denkers Eric Y. 
Published: July 2002

ABSTRACTThe immunomodulatory role of neutrophils during infection withToxoplasma gondiiwas investigated. Monoclonal antibody-mediated depletion revealed that neutrophils are essential for survival during the first few days of infection. Moreover, neutrophil depletion was associated with a weaker type 1 immune response as measured by decreased levels of gamma interferon, interleukin-12 (IL-12) and tumor necrosis factor alpha. IL-10 was also decreased in depleted animals. Additionally, splenic populations of CD4+T cells, CD8+T cells, and NK1.1+cells were decreased in depleted mice. Neutrophil-depleted mice exhibited lesions of greater severity in tissues examined and a greater parasite burden as determined by histopathology and reverse transcription-PCR. We conclude that neutrophils are critical near the time of infection because they influence the character of the immune response and control tachyzoite replication.
Role of Trehalose Dimycolate in Recruitment of Cells and Modulation of Production of Cytokines and NO in Tuberculosis
Authors: Lima Valéria M. F. , Bonato Vania L. D. , Lima Karla M. , Dos Santos Sandra A. , Dos Santos Rubens R. , Gonçalves Eduardo D. C. , Faccioli Lucia H. , Brandão Izaira T. , Rodrigues-Junior José M. , Silva Célio L. 
Published: July 2002

ABSTRACTMice treated with viableMycobacterium tuberculosiswith no glycolipid trehalose dimycolate (TDM) on the outer cell wall (delipidatedM. tuberculosis) by intraperitoneal or intratracheal inoculation presented an intense recruitment of polymorphonuclear cells into the peritoneal cavity and an acute inflammatory reaction in the lungs, respectively. In addition, lung lesions were resolved around the 32nd day after intratracheal inoculation. TDM-loaded biodegradable poly-dl-lactide-coglycolide microspheres as well as TDM-coated charcoal particles induced an intense inflammatory reaction. In addition, high levels of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-12, IL-10, gamma interferon (IFN-γ), and IL-4 production were detected in lung cells, and nitric oxide (NO) production was high in culture supernatants of bronchoalveolar lavage cells. These in vivo data were confirmed by in vitro experiments using peritoneal macrophages cultured in the presence of TDM adsorbed onto coverslips. High levels of IFN-γ, IL-6, TNF-α, IL-12, IL-10, and NO were detected in the culture supernatants. Our results suggest that TDM contributes to persistence of infection through production of cytokines, which are important for the recruitment of inflammatory cells and maintenance of a granulomatous reaction. In addition, our findings are important for a better understanding of the immunostimulatory activity of TDM and its possible use as an adjuvant in experiments using DNA vaccine or gene therapy against tuberculosis.
Changes in Availability of Oxygen Accentuate Differences in Capsular Polysaccharide Expression by Phenotypic Variants and Clinical Isolates of
Streptococcus pneumoniae
Authors: Weiser Jeffrey N. , Bae Deborah , Epino Henry , Gordon Stephen B. , Kapoor Miki , Zenewicz Lauren A. , Shchepetov Mikhail 
Published: July 2002

ABSTRACT

Most isolates of
Streptococcus pneumoniae
are mixed populations of transparent (T) and opaque (O) colony phenotypes. Differences in the production of capsular polysaccharide (CPS) between O and T variants were accentuated by changes in the environmental concentration of oxygen. O variants demonstrated a 5.2- to 10.6-fold increase in amounts of CPS under anaerobic compared to atmospheric growth conditions, while CPS production remained low under all conditions for T variants. Increased amounts of CPS in O compared to T pneumococci were associated with increased expression of
cps
-encoded proteins. The inhibitory effect of oxygen on expression of CPS in O variants correlated with decreased tyrosine phosphorylation of CpsD, a tyrosine kinase and regulator of CPS synthesis. Modulation of CpsD expression and its activity by tyrosine phosphorylation may allow the pneumococcus to adapt to the requirements of both colonization, where decreased CPS allows for adherence, and bacteremia, where increased CPS may be required to escape from opsonic clearance. In patients with invasive infection, paired isolates from the same patient were shown to have predominately a T colony phenotype without phosphotyrosine on CpsD when cultured from the nasopharynx, and an O phenotype that phosphorylates CpsD in response to oxygen when cultured from the blood. Differences in the availability of oxygen, therefore, may be a key factor in allowing for the selection of distinct phenotypes in these two host environments.
Laccase of
Cryptococcus neoformans
Is a Cell Wall-Associated Virulence Factor
Authors: Zhu Xudong , Gibbons Jack , Garcia-Rivera Javier , Casadevall Arturo , Williamson Peter R. 
Published: July 2002

ABSTRACT

Virulence is the outcome of an interaction between the host and a microbe and is characterized by a large array of opposing reactions operating at the host-pathogen interface.
Cryptococcus neoformans
is an important opportunistic pathogen in immunocompromised patients, including those with human immunodeficiency virus, and expresses a virulence-associated laccase which is believed to oxidize brain catecholamines and iron as a defense against host immune cells. In the present report, we investigated the cellular location of laccase to understand more fully how it contributes to cryptococcal virulence. A monoclonal antibody to the
C. neoformans
laccase was generated and used to show localization in the cell walls of representative serotype A (H99) and serotype D (B-3501) strains by immunoelectron microscopy. In addition, confocal microscopy was used to show a peripheral location of green fluorescent protein-tagged laccase expressed in live H99 cells. Biochemical studies showed that laccase could be released from intact cells or cell wall fractions with glucanase enzymes but was retained in the cell wall after sequential extraction with 1 M NaCl, 6 M urea, and 1% sodium dodecyl sulfate. The presence of a hydrolyzable bond linking laccase to the cell wall was suggested by removal of laccase from cell wall preparations after they were boiled in 1% sodium dodecyl sulfate, as was the presence of a disulfide or thioester bond by removal with dithiothreitol or β-mercaptoethanol. These data show that laccase is present as a tightly associated cell wall enzyme that is readily accessible for interactions with host immune cells.
Immunodominant Epitopes inBabesia bovisRhoptry-Associated Protein 1 That Elicit Memory CD4+-T-Lymphocyte Responses inB. bovis-Immune Individuals Are Located in the Amino-Terminal Domain
Authors: Norimine Junzo , Suarez Carlos E. , McElwain Terry F. , Florin-Christensen Monica , Brown Wendy C. 
Published: July 2002

ABSTRACTBabesia bovisrhoptry-associated protein 1 (RAP-1), which confers partial protection againstB. bovischallenge, is recognized by antibodies and T lymphocytes from cattle that have recovered from infection and are immune to subsequent challenge. RAP-1 is a 60-kDa protein with an N-terminal (NT) region that contains four cysteine residues conserved among allBabesiaRAP-1 family members and a C-terminal (CT) region that contains multiple, degenerate, tandem 23-amino-acid (aa) repeats. To define the location of CD4+-T-cell epitopes for vaccine development using a recombinant protein or minigene construct, a series of truncated recombinant RAP-1 proteins and peptides were tested for stimulation of T-cell lines derived fromB. bovis-immune cattle. CD4+-T-cell lines from threeB. bovis-immune cattle with differentDRB3haplotypes responded to the NT region of RAP-1, whereas T cells from only one animal responded weakly to the CT region. T-cell lines from the three individuals recognized two to six NT-region peptides spanning aa 134 to 316 and representing at least four dominant epitopes. Using RAP-1-specific CD4+-T-cell clones, two NT-region epitopes, EYLVNKVLYMATMNYKT (aa 187 to 203) and EAPWYKRWIKKFR (aa 295 to 307), and one CT-region repeat epitope, FREAPQATKHFL, which is present twice at aa positions 391 to 402 and 414 to 425, were identified. Several peptides representing degenerate repeats of the agonist CT-region peptide FREAPQATKHFL neither stimulated responses of T-cell clones specific for this peptide nor inhibited responses to the agonist peptide. Upon stimulation with specific antigen, T-cell clones specific for NT or CT epitopes produced gamma interferon. The presence of T-helper-cell epitopes in the NT domain of RAP-1, which is highly conserved among otherwise antigenically different strains ofB. bovis, supports the inclusion of this region in vaccine constructs to be tested in cattle.
The In Vitro Interaction ofStreptococcus pyogeneswith Human Pharyngeal Cells Induces a Phage-Encoded Extracellular DNase
Authors: Broudy Thomas B. , Pancholi Vijaykumar , Fischetti Vincent A. 
Published: July 2002

ABSTRACTThe role lysogenic bacteriophage play in the pathogenesis of the host bacterium is poorly understood. In a previous study, we found that streptococcal coculture with human pharyngeal cells resulted in the induction of lysogenic bacteriophage as well as the phage-associated streptococcal pyrogenic exotoxin C (SpeC). In this study, we have determined that in addition to SpeC induction, a number of other streptococcal proteins are also released by the bacteria during coculture with pharyngeal cells. Among these, we identified and characterized a novel 27-kDa secreted protein. Sequence analysis of this novel protein demonstrated it to be encoded by the same lysogenic bacteriophage which harborsspeC. Protein sequence analysis revealed varied homologies with several streptococcal DNases. Further biochemical characterization of the recombinantly expressed protein verified it to be a divalent cation-dependent streptococcal phage-encoded DNase (Spd1). Although functionally distinct, SpeC and Spd1 are associated by a number of parameters, including genetic proximity and transcriptional regulation. Finally, we speculate on the induction of phage-encoded DNase (Spd1) enhancing the fitness of both bacteria and phage.
Entamoeba histolytica
Lectins Contain Unique 6-Cys or 8-Cys Chitin-Binding Domains
Authors: Van Dellen Katrina , Ghosh Sudip K. , Robbins Phillips W. , Loftus Brendan , Samuelson John 
Published: July 2002

ABSTRACT

The Jacob lectin, the most abundant glycoprotein in the cyst wall of
Entamoeba invadens
, contains five unique 6-Cys chitin-binding domains (CBDs). We identified
Entamoeba histolytica
and
Entamoeba dispar
genes encoding Jacob homologues, each of which contains two predicted 6-Cys CBDs. A unique 8-Cys CBD was found at the N termini of the
E. histolytica
chitinase and three other predicted lectins, called Jessie 1 to Jessie 3. The CBDs of four
E. histolytica
lectins (Jacob, chitinase, and Jessies 2 and 3) were expressed in secretory vesicles of transfected amebae and shown to bind to particulate chitin.
Dual Control of Streptokinase and Streptolysin S Production by thecovRSandfasCAXTwo-Component Regulators inStreptococcus dysgalactiaesubsp.equisimilis
Authors: Steiner Kerstin , Malke Horst 
Published: July 2002

ABSTRACTSynthesis of the plasminogen activator streptokinase (SK) by group A streptococci (GAS) has recently been shown to be subject to control by two two-component regulators,covRS(orcsrRS) andfasBCA. In independent studies, response regulator CovR proved to act as the repressor, whereas FasA was found to act indirectly as the activator by controlling the expression of a stimulatory RNA,fasX. In an attempt at understanding the regulation of SK production in the human group C streptococcal (GCS) strain H46A, the strongest SK producer known yet, we provide here physical and functional evidence for the presence of thecovandfassystems in GCS as well and, using a mutational approach, compare the balance between their opposing actions in H46A and GAS strain NZ131. Sequence analysis combined with Southern hybridization revealed that thecovRSandfasCAXoperons are preserved at high levels of primary structure identity between the corresponding GAS and GCS genes, with the exception offasB, encoding a second sensor kinase that is not a member of the GCSfasoperon. This analysis also showed that wild-type H46A is actually a derepressed mutant for SK and streptolysin S (SLS) synthesis, carrying a K102 amber mutation incovR.Usingcovandfasmutations in various combinations together with strain constructs allowing complementation intrans, we found that, in H46A,covandfascontribute to approximately equal negative and positive extents, respectively, to constitutive SK and SLS activity. The amounts of SK paralleled the level ofskcH46Atranscription. The most profound difference between H46A and NZ131 regarding the relative activities of thecovandfassystems consisted in significantly higher activity of a functional CovR repressor in NZ131 than in H46A. In NZ131, CovR decreased SK activity in a Fas+background about sevenfold, compared to a 1.9-fold reduction of SK activity in H46A. Combined with the very short-lived nature ofcovRmRNA (decay rate, 1.39/min), such differences may contribute to strain-specific peculiarities of the expression of two prominent streptococcal virulence factors in response to environmental changes.
Chronic Helminth Infection Induces Alternatively Activated Macrophages Expressing High Levels of CCR5 with Low Interleukin-12 Production and Th2-Biasing Ability
Authors: Rodríguez-Sosa Miriam , Satoskar Abhay R. , Calderón Rodrigo , Gomez-Garcia Lorena , Saavedra Rafael , Bojalil Rafael , Terrazas Luis I. 
Published: July 2002

ABSTRACTHelminth infections induce Th2-type biased immune responses. Although the mechanisms involved in this phenomenon are not yet clearly defined, antigen-presenting cells (APC) could play an important role in this process. Here, we have used peritoneal macrophages (F4/80+) recruited at different times after challenge withTaenia crassicepsas APC and tested their ability to regulate Th1/Th2 differentiation. Macrophages from acute infections produced high levels of interleukin-12 (IL-12) and nitric oxide (NO), paralleled with low levels of IL-6 and prostaglandin E2(PGE2) and with the ability to induce strong antigen-specific CD4+ T-cell proliferation in response to nonrelated antigens. In contrast, macrophages from chronic infections produced higher levels of IL-6 and PGE2and had suppressed production of IL-12 and NO, associated with a poor ability to induce antigen-specific proliferation in CD4+ T cells. Failure to induce proliferation was not due to a deficient expression of accessory molecules, since major histocompatibility complex class II, CD40, and B7-2 were up-regulated, together with CD23 and CCR5 as infection progressed. These macrophages from chronic infections were able to bias CD4+ T cells to produce IL-4 but not gamma interferon (IFN-γ), contrary to macrophages from acute infections. Blockade of B7-2 and IL-6 and inhibition of PGE2failed to restore the proliferative response in CD4+ T cells. Furthermore, studies using STAT6−/−mice revealed that STAT6-mediated signaling was essential for the expansion of these alternatively activated macrophages. These data demonstrate that helminth infections can induce different macrophage populations that have Th2-biasing properties.
Strain-Dependent Induction of Enterocyte Apoptosis byGiardia lambliaDisrupts Epithelial Barrier Function in a Caspase-3-Dependent Manner
Authors: Chin Alex C. , Teoh Desiree A. , Scott Kevin G.-E. , Meddings Jonathon B. , Macnaughton Wallace K. , Buret Andre G. 
Published: July 2002

ABSTRACTWe recently demonstrated thatGiardia lambliarearranges cytoskeletal proteins and reduces transepithelial electrical resistance. The effect ofG. lambliaon enterocyte apoptosis is unknown, and a possible link between microbially induced enterocyte apoptosis and altered epithelial permeability has yet to be established. The aim of this study was to assess whetherG. lambliainduces enterocyte apoptosis in duodenal epithelial monolayers and whether this effect increases epithelial permeability. Monolayers of nontransformed human duodenal epithelial cells were incubated with sonicated or liveG. lambliatrophozoites (NF, S2, WB, or PB strains) for 8, 24, and 48 h. Cell cultures were assessed for apoptosis by Hoechst fluorescence staining, enzyme-linked immunosorbent assay for apoptotic nucleosomes, and electron microscopy. In separate experiments, monolayers were pretreated with or without 120 μM caspase-3 inhibitor (Z-DEVD-FMK) for 1 h and were assessed for production of apoptotic nucleosomes, tight junctional integrity (with fluorescent ZO-1 staining followed by confocal laser microscopy), and transepithelial permeability for fluorescein isothiocyanate-dextran.G. lambliastrains NF and S2, but not strains WB or PB, induced enterocyte apoptosis within the monolayers, and this effect was inhibited by Z-DEVD-FMK pretreatment. Using theG. lambliaNF isolate, additional experiments investigated the possible link between enterocyte apoptosis and altered epithelial permeability.G. lambliaNF disrupted tight junctional ZO-1 and increased epithelial permeability, but these effects were also prevented by pretreatment with the caspase-3 inhibitor. These findings indicate that strain-dependent induction of enterocyte apoptosis may contribute to the pathogenesis of giardiasis. This effect is responsible for a loss of epithelial barrier function by disrupting tight junctional ZO-1 and increasing permeability in a caspase-3-dependent manner.
Catabolism of α-Ketoglutarate by a
sucA
Mutant of
Bradyrhizobium japonicum
: Evidence for an Alternative Tricarboxylic Acid Cycle
Authors: Green Laura S. , Li Youzhong , Emerich David W. , Bergersen Fraser J. , Day David A. 
Published: July 2002

ABSTRACT

A complete tricarboxylic acid (TCA) cycle is generally considered necessary for energy production from the dicarboxylic acid substrates malate, succinate, and fumarate. However, a
Bradyrhizobium japonicum sucA
mutant that is missing α-ketoglutarate dehydrogenase is able to grow on malate as its sole source of carbon. This mutant also fixes nitrogen in symbiosis with soybean, where dicarboxylic acids are its principal carbon substrate. Using a flow chamber system to make direct measurements of oxygen consumption and ammonium excretion, we confirmed that bacteroids formed by the
sucA
mutant displayed wild-type rates of respiration and nitrogen fixation. Despite the absence of α-ketoglutarate dehydrogenase activity, whole cells of the mutant were able to decarboxylate α-[U-
14
C]ketoglutarate and [U-
14
C]glutamate at rates similar to those of wild-type
B. japonicum
, indicating that there was an alternative route for α-ketoglutarate catabolism. Because cell extracts from
B. japonicum
decarboxylated [U-
14
C]glutamate very slowly, the γ-aminobutyrate shunt is unlikely to be the pathway responsible for α-ketoglutarate catabolism in the mutant. In contrast, cell extracts from both the wild type and mutant showed a coenzyme A (CoA)-independent α-ketoglutarate decarboxylation activity. This activity was independent of pyridine nucleotides and was stimulated by thiamine PP
i
. Thin-layer chromatography showed that the product of α-ketoglutarate decarboxylation was succinic semialdehyde. The CoA-independent α-ketoglutarate decarboxylase, along with succinate semialdehyde dehydrogenase, may form an alternative pathway for α-ketoglutarate catabolism, and this pathway may enhance TCA cycle function during symbiotic nitrogen fixation.
Relative Roles of the
fla/che
P
A
, P
D-3
, and P

sigD

Promoters in Regulating Motility and
sigD
Expression in
Bacillus subtilis
Authors: West Joyce T. , Estacio William , Márquez-Magaña Leticia 
Published: July 2002

ABSTRACT

Three promoters have been identified as having potentially important regulatory roles in governing expression of the
fla/che
operon and of
sigD
, a gene that lies near the 3′ end of the operon. Two of these promoters,
fla/che
P
A
and P
D-3
, lie upstream of the >26-kb
fla/che
operon. The third promoter, P

sigD

, lies within the operon, immediately upstream of
sigD. fla/che
P
A
, transcribed by Eς
A
, lies ≥24 kb upstream of
sigD
and appears to be largely responsible for
sigD
expression. P
D-3
, transcribed by Eς
D
, has been proposed to participate in an autoregulatory positive feedback loop. P

sigD

, a minor ς
A
-dependent promoter, has been implicated as essential for normal expression of the
fla/che
operon. We tested the proposed functions of these promoters in experiments that utilized strains that bear chromosomal deletions of
fla/che
P
A
, P
D-3
, or P

sigD

. Our analysis of these strains indicates that
fla/che
P
A
is absolutely essential for motility, that P
D-3
does not function in positive feedback regulation of
sigD
expression, and that P

sigD

is not essential for normal
fla/che
expression. Further, our results suggest that an additional promoter(s) contributes to
sigD
expression.