bluuebunny/crossref_metadata_2025_split huggingface dataset:
BIOCHEMICAL CHARACTERIZATION OF SOME TUNISIAN OLIVE OILS
Authors: DHIFI W. , HAMROUNI I. , AYACHI S. , CHAHED T. , SAÏDANI M. , MARZOUK B. 
Published: March 2005

ABSTRACTFour samples of Tunisian virgin olive oils of Chetoui, Chemlali, Chemchali and Oueslati varieties were analyzed for their chemical and fatty acid, total chlorophyll, total polyphenol and total aroma contents. The results showed that Chetoui was the most pigmented oil (4.45 ppm) and Oueslati oil contained the smallest amount of total chlorophylls (1.29 ppm). The Chetoui oil had the highest amount (94.37 ppm) of total polyphenols, while the Oueslati had the lowest amount (65.5 ppm). Furthermore, the Chemchali oil contained the highest level of total aroma (55.49 µg/mL of oil), followed by the Chemlali, Chetoui and Oueslati oils. The Chetoui oil was characterized by the highest level of oleic acid (70.9%) in contrast to the Chemlali, which had the lowest level of this fatty acid (58.6%). In addition, the highest level of palmitic acid characterizes the oil Chemlali (19.7%), whereas the Chetoui had the lowest (9.1%).
Pleiotropic Enhancement of Bacterial Pathogenesis Resulting from the Constitutive Activation of theListeria monocytogenesRegulatory Factor PrfA
Authors: Mueller Kimberly J. , Freitag Nancy E. 
Published: March 2005

ABSTRACTListeria monocytogenesis a facultative intracellular bacterial pathogen that causes serious disease in immunocompromised individuals, pregnant women, and neonates. Bacterial virulence is mediated by the expression of specific gene products that facilitate entry into host cells and enable bacterial replication; the majority of these gene products are regulated by a transcriptional activator known as PrfA.L. monocytogenesstrains containingprfAE77K orprfAG155S mutations exhibit increased expression of virulence genes in broth culture and are hypervirulent in mice. To define the scope of the influences of theprfAE77K andprfAG155S mutations onL. monocytogenespathogenesis, multiple aspects of bacterial invasion and intracellular growth were examined. Enhanced bacterial invasion of host epithelial cells was dependent on the expression of a number of surface proteins previously associated with invasion, including InlA, InlB, and ActA. In addition to these surface proteins, increased production of thehly-encoded secreted hemolysin listeriolysin O (LLO) was also found to significantly enhance bacterial invasion into epithelial cell lines for bothprfAmutant strains. AlthoughprfAE77K andprfAG155S strains were similar in their invasive phenotypes, the infection of epithelial cells withprfAE77K strains resulted in host cell plasma membrane damage, whereasprfAG155S strains did not alter plasma membrane integrity. Bacterial infection of human epithelial cells, in which the production of LLO is not required for bacterial entry into the cytosol, indicated thatprfAE77K cytotoxic effects were mediated via LLO. BothprfAE77K andprfAG155S strains were more efficient than wild-type bacteria in gaining access to the host cell cytosol and in initiating the polymerization of host cell actin, and both were capable of mediating LLO-independent lysis of host cell vacuoles in cell lines for whichL. monocytogenesvacuole disruption normally requires LLO activity. These experiments illuminate the diverse facets ofL. monocytogenespathogenesis that are significantly enhanced by the constitutive activation of PrfA viaprfAmutations and underscore the critical role of this protein in promotingL. monocytogenesvirulence.
The
Actinobacillus actinomycetemcomitans
Autotransporter Adhesin Aae Exhibits Specificity for Buccal Epithelial Cells from Humans and Old World Primates
Authors: Fine Daniel H. , Velliyagounder Kabilan , Furgang David , Kaplan Jeffrey B. 
Published: March 2005

ABSTRACT

Cells of the gram-negative periodontopathogen
Actinobacillus actinomycetemcomitans
express a surface-exposed, outer membrane autotransporter protein, designated Aae, which has been implicated in epithelial cell binding. We constructed a mutant strain of
A. actinomycetemcomitans
that contained a transposon insertion in the Aae structural gene (
aae
) and tested the mutant to determine its ability to bind to buccal epithelial cells (BECs) isolated from healthy volunteers. Significantly fewer mutant cells than wild-type cells bound to BECs. A broad-host-range plasmid that contained an intact
aae
gene driven by a heterologous
tac
promoter restored the ability of the mutant strain to bind to BECs at wild-type levels. This plasmid also conferred upon
Escherichia coli
the ability to express the Aae protein on its surface and to bind to human BECs. Aae-expressing
E. coli
also bound to BECs isolated from six Old World primates but not to BECs isolated from four New World primates or nine other nonprimate mammals, as well as to human gingival epithelial cells but not to human pharyngeal, palatal, tongue, bronchial, or cervical epithelial cells. Our findings indicate that Aae mediates binding of
A. actinomycetemcomitans
to BECs from humans and Old World primates and that this process may contribute to the host range specificity and tissue tropism exhibited by this bacterium.
Biofilm Formation by
Neisseria gonorrhoeae
Authors: Greiner L. L. , Edwards J. L. , Shao J. , Rabinak C. , Entz D. , Apicella M. A. 
Published: March 2005

ABSTRACT

Studies were performed in continuous-flow chambers to determine whether
Neisseria gonorrhoeae
could form a biofilm. Under these growth conditions,
N. gonorrhoeae
formed a biofilm with or without the addition of 10 μM sodium nitrite to the perfusion medium. Microscopic analysis of a 4-day growth of
N. gonorrhoeae
strain 1291 revealed evidence of a biofilm with organisms embedded in matrix, which was interlaced with water channels.
N. gonorrhoeae
strains MS11 and FA1090 were found to also form biofilms under the same growth conditions. Cryofield emission scanning electron microscopy and transmission electron microscopy confirmed that organisms were embedded in a continuous matrix with membranous structures spanning the biofilm. These studies also demonstrated that
N. gonorrhoeae
has the capability to form a matrix in the presence and absence of CMP-
N
-acetylneuraminic acid (CMP-Neu5Ac). Studies with monoclonal antibody 6B4 and the lectins soy bean agglutinin and
Maackia amurensis
indicated that the predominate terminal sugars in the biofilm matrix formed a lactosamine when the biofilm was grown in the absence of CMP-Neu5Ac and sialyllactosamine in the presence of CMP-Neu5Ac.
N. gonorrhoeae
strain 1291 formed a biofilm on primary urethral epithelial cells and cervical cells in culture without loss of viability of the epithelial cell layer. Our studies demonstrated that
N. gonorrhoeae
can form biofilms in continuous-flow chambers and on living cells. Studies of these biofilms may have implications for understanding asymptomatic gonococcal infection.
Mast Cells Limit Systemic Bacterial Dissemination but Not Colitis in Response toCitrobacter rodentium
Authors: Wei Olivia L. , Hilliard Ashley , Kalman Daniel , Sherman Melanie 
Published: March 2005

ABSTRACTEnteropathogenicEscherichia coliand enterohemorrhagicE. colicause an inflammatory colitis in human patients characterized by neutrophil infiltration, proinflammatory cytokine expression, and crypt hyperplasia.Citrobacter rodentiumcauses a similar colitis in mice and serves as a model for enteropathogenicE. coliinfection in humans.C. rodentiuminduces systemic T-cell-dependent antibody production that facilitates clearance of the bacteria and protects the host from reinfection. The role of innate immune cells in infectious colitis, however, is less well understood. In this study, we have determined the role of mast cells in the inflammatory response and disease induced byC. rodentium. Mice deficient in mast cells exhibit more severe colonic histopathology and have a higher mortality rate following infection withC. rodentiumthan do wild-type animals. Despite unimpaired neutrophil recruitment and lymphocyte activation, mast cell-deficient mice have a disseminated infection evident in crucial organ systems that contributes to sepsis. Importantly, mast cells also have the capacity to directly killC. rodentium. Together, these results suggest that mast cells protect the host from systemic infection by reducing the bacterial load and preventing dissemination of the bacterium from the colon.
FatalPlasmodium falciparumMalaria Causes Specific Patterns of Splenic Architectural Disorganization
Authors: Urban Britta C. , Hien Tran T. , Day Nicholas P. , Phu Nguyen H. , Roberts Rachel , Pongponratn Emsri , Jones Margret , Mai Nguyen T. H. , Bethell Delia , Turner Gareth D. H. , Ferguson David , White Nicholas J. , Roberts David J. 
Published: March 2005

ABSTRACTThe spleen is critical for host defense against pathogens, includingPlasmodium falciparum. It has a dual role, not only removing aged or antigenically altered erythrocytes from the blood but also as the major lymphoid organ for blood-borne or systemic infections. The human malaria parasiteP. falciparumreplicates within erythrocytes during asexual blood stages and causes repeated infections that can be associated with severe disease. In spite of the crucial role of the spleen in the innate and acquired immune response to malaria, there is little information on the pathology of the spleen in human malaria. We performed a histological and quantitative immunohistochemical study of spleen sections from Vietnamese adults dying from severe falciparum malaria and compared the findings with the findings for spleen sections from control patients and patients dying from systemic bacterial sepsis. Here we report that the white pulp in the spleens of patients dying from malaria showed a marked architectural disorganization. We observed a marked dissolution of the marginal zones with relative loss of B cells. Furthermore, we found strong HLA-DR expression on sinusoidal lining cells but downregulation on cordal macrophages.P. falciparuminfection results in alterations in splenic leukocytes, many of which are not seen in sepsis.
Pyrophosphatase of the RoundwormAscaris suumPlays an Essential Role in the Worm's Molting and Development
Authors: Islam M. Khyrul , Miyoshi Takeharu , Yamada Manabu , Tsuji Naotoshi 
Published: March 2005

ABSTRACTPrevious studies indicated that inorganic pyrophosphatase ofAscaris suum(AsPPase) plays an important role in larval survival in the host. Here we describe a precise role for AsPPase in larval molting and development and also describe the potential role of recombinant AsPPase (rAsPPase) in protective immunity toA. suuminfection. Using reverse transcriptase PCR analysis, we found that disruption of AsPPase gene function by RNA interference resulted in suppression of AsPPase mRNA levels. RNA interference also caused inhibition of molting of third-stage larvae (31%) and suppression of native protein expression, as demonstrated by a 56% reduction in enzyme activity and quantified by immunoblot and immunofluorescence analyses, suggesting that AsPPase has a role in the molting process. The anatomic location of the AsPPase native enzyme in the hypodermis of larvae along with its elevated expression prior to and during the molting process supports such a role. Anti-rAsPPase immunoglobulin G (IgG) also resulted in 57% inhibition of molting ofA. suumlung-stage third-stage larvae to fourth-stage larvae in vitro with developmental arrest. Antigenic epitopes of AsPPase overlapped the enzyme active sites. Mice immunized with rAsPPase exhibited high antigen-specific IgG antibody responses and were protected (>70%) against a challengeA. suummigratory-phase infection. Splenic T cells from rAsPPase-immunized mice produced low levels of T helper 1-type cytokines (gamma interferon and interleukin-2) in vitro but exhibited an elevated interleukin-10 response. A significantly high level of IgG1 subclass antibodies was found in immunized mice. Our results establish that AsPPase has a critical role in the molting and development ofAscarisroundworms and suggest the potential of AsPPase for use as a candidate vaccine against ascariasis.
Melanization ofCryptococcus neoformansAffects Lung Inflammatory Responses during Cryptococcal Infection
Authors: Mednick Aron J. , Nosanchuk Joshua D. , Casadevall Arturo 
Published: March 2005

ABSTRACTThe production of melanin pigments is associated with virulence for many microbes. Melanin is believed to contribute to microbial virulence by protecting microbial cells from oxidative attack during infection. However, there is also evidence from various systems that melanins have immunomodulatory properties, which conceivably could contribute to virulence by altering immune responses. To investigate the effect of melanin on the immune response, we compared the murine pulmonary responses to infection with melanized and nonmelanizedCryptococcus neoformanscells. Infection with melanized cells resulted in a greater fungal burden during the early stages of infection and was associated with higher levels of interleukin-4 and MCP-1 and greater numbers of infiltrating leukocytes. Infection with laccase-positive (melanotic)C. neoformanscells also elicited higher MCP-1 levels and more infiltrating leukocytes than did infection with laccase-negative cells. Melanization interfered with phagocytosis in vivo for encapsulatedC. neoformansbut not for nonencapsulated cells. The results provide strong evidence that cryptococcal melanization can influence the immune response to infection and suggest that immunomodulation is an additional mechanism by which the pigment contributes to virulence.
The
Legionella pneumophila tatB
Gene Facilitates Secretion of Phospholipase C, Growth under Iron-Limiting Conditions, and Intracellular Infection
Authors: Rossier Ombeline , Cianciotto Nicholas P. 
Published: March 2005

ABSTRACT

Our previous mutational analysis of
Legionella pneumophila
demonstrated a role for type II protein (Lsp) secretion and iron acquisition in intracellular infection and virulence. In gram-negative bacteria, the twin-arginine translocation (Tat) pathway is involved in secretion of proteins, including components of respiratory complexes, across the inner membrane to the periplasm. To assess the significance of Tat for
L. pneumophila
,
tatB
mutants were characterized. The mutants exhibited normal growth in standard media but grew slowly under low-iron conditions. They were also impaired in the Nadi assay, indicating that the function of cytochrome
c
oxidase is influenced by
tatB
. Consistent with this observation, a subunit of the cytochrome
c
reductase was shown to be a Tat substrate. Supernatants of the
tatB
mutants showed a 30% reduction in phospholipase C activity while maintaining normal levels of other Lsp secreted activities. When tested for infection of U937 macrophages, the
tatB
mutants showed a 10-fold reduction in growth. Double mutants lacking
tatB
and Lsp secretion were even more defective, suggesting
tatB
has an intracellular role that is independent of Lsp.
tatB
mutants were also impaired 20-fold in
Hartmannella vermiformis
amoebae cultured in the presence of an iron chelator. All mutant phenotypes were complemented by reintroduction of an intact
tatB
. Thus,
L. pneumophila tatB
plays a role in the formation of a respiratory complex, growth under low-iron conditions, the secretion of a phospholipase C activity, and intracellular infection.
Avoidance of the Host Immune System through Phase Variation in
Mycoplasma pulmonis
Authors: Denison Amy M. , Clapper Brenda , Dybvig Kevin 
Published: March 2005

ABSTRACT

Phase-variable lipoproteins are commonly found in
Mycoplasma
species.
Mycoplasma pulmonis
contains a family of extensively studied phase- and size-variable lipoproteins encoded by the
vsa
locus. The Vsa surface proteins vary at a high frequency, the in vivo significance of which has yet to be determined. We investigated the role of Vsa phase variation in respect to tissue tropism and avoidance of the immune system in the mouse host. Mycoplasmas were cultured 3, 14, and 21 days postinoculation from the nose, lung, trachea, liver, and spleen of experimentally infected C57BL/6 (wild-type), C57BL/6-RAG-1
−/−
(RAG
−/−
), and C57BL/6-inducible nitric oxide synthase (iNOS)
−/−
(iNOS
−/−
) mice. In wild-type and iNOS
−/−
mice, a large number of Vsa variants were seen by 21 days postinoculation. In contrast, little Vsa variation occurred in all tissues of RAG
−/−
mice. Analysis of isolates from 14 days postinoculation revealed less variation of the Vsa proteins in iNOS
−/−
mice than in the wild type. Western blot analysis of isolates from each strain of mouse demonstrated that Vsa phase variation occurred independently of size variation, indicating no obvious selection pressure for size variants. Additionally, these experiments provided no evidence that mycoplasmas producing particular Vsa proteins adhered only to specific tissues. The data strongly indicate that Vsa phase variation is a mechanism for avoidance of the immune system with no obvious contribution to tissue tropism.
Impact of the SpeB Protease on Binding of the Complement Regulatory Proteins Factor H and Factor H-Like Protein 1 byStreptococcus pyogenes
Authors: Wei Lin , Pandiripally Vinod , Gregory Eugene , Clymer Micaya , Cue David 
Published: March 2005

ABSTRACTMicrobial pathogens often exploit human complement regulatory proteins such as factor H (FH) and factor H-like protein 1 (FHL-1) for immune evasion. Fba is an FH and FHL-1 binding protein expressed on the surface of the human pathogenic bacteriumStreptococcus pyogenes, a common agent of pharyngeal, skin, and soft-tissue infections. Fba has been shown to contribute to phagocytosis resistance, intracellular invasion, and virulence in mice. Here, we look at the role of Fba in recruitment of FH and FHL-1 by five serotype M1 isolates of streptococci. Inactivation offbagreatly inhibited binding of FH and FHL-1 by all isolates, indicating that Fba is a major FH and FHL-1 binding factor of serotype M1 streptococci. For three isolates, FH binding was significantly reduced in stationary-phase cultures and correlated with high levels of protease activity and SpeB (an extracellular cysteine protease) protein in culture supernatants. Analysis of aspeBmutant confirmed that SpeB accounts for the loss of Fba from the cell surface, suggesting that the protease may modulate FH and FHL-1 recruitment during infection. Comparisons offbaDNA sequences revealed that the FH and FHL-1 binding site in Fba is conserved among the M1 isolates. Although the ligand binding site is not strictly conserved in Fba from a serotype M49 isolate, the M49 Fba protein was found to bind both FH and FHL-1. Collectively, these data indicate that binding of FH and FHL-1 is a conserved function of Fba while modulation of Fba function by SpeB is variable.
Carbohydrate-Binding Specificity of the
Escherichia coli
Cytolethal Distending Toxin CdtA-II and CdtC-II Subunits
Authors: McSweeney Leslie A. , Dreyfus Lawrence A. 
Published: March 2005

ABSTRACT

Intoxication by cytolethal distending toxin depends on assembly of CdtB, the active A component of this AB toxin, with the cell surface-binding (B) component, composed of the CdtA-CdtC heterodimer, to form the active holotoxin. Here we examine the cell surface binding properties of
Escherichia coli
-derived CdtA-II (CdtA-II
Ec
) and CdtC-II
Ec
and their capacity to provide a binding platform for CdtB-II
Ec
. Using a flow cytometry-based binding assay, we demonstrate that CdtB-II
Ec
binds to the HeLa cell surface in a CdtA-II
Ec
- and CdtC-II
Ec
-dependent manner and that CdtA-II
Ec
and CdtC-II
Ec
compete for the same structure on the HeLa cell surface. Preincubation of cells with glycoproteins (thyroglobulin and fetuin), but not simple sugars, blocks surface binding of CdtA-II
Ec
and CdtC-II
Ec
. Moreover, CdtA-II
Ec
and CdtC-II
Ec
bind immobilized fetuin and thyroglobulin as well as fucose and to a lesser degree
N
-acetylgalactoseamine and
N
-acetylglucoseamine. Removal of N- but not O-linked carbohydrates from fetuin and thyroglobulin prevents binding of CdtA-II
Ec
and CdtC-II
Ec
to these glycoproteins. In addition, removal of N- but not O-linked surface sugar attachments prevents CDT-II
Ec
intoxication. To characterize the cell surface ligand recognized by CdtA-II
Ec
and CdtC-II
Ec
, lectins having various carbohydrate specificities were used to block CDT activity and the cell surface binding of CdtA-II
Ec
and CdtC-II
Ec
. Pretreatment of cells with AAA, SNA-I, STA, UEA-I, GNA, and NPA partially or completely blocked CDT activity. AAA, EEA, and UEA-I lectins, all having specificity for fucose, blocked surface binding of CdtA-II
Ec
and CdtC-II
Ec
. Together, our data indicate that CdtA-II
Ec
and CdtC-II
Ec
bind an N-linked fucose-containing structure on HeLa cells.
Redundant Roles for Met Docking Site Tyrosines and the Gab1 Pleckstrin Homology Domain in InlB-Mediated Entry of
Listeria monocytogenes
Authors: Basar Tumay , Shen Yang , Ireton Keith 
Published: March 2005

ABSTRACT

The bacterial pathogen
Listeria monocytogenes
causes food-borne illnesses leading to gastroenteritis, meningitis, or abortion.
Listeria
induces its internalization into some mammalian cells through interaction of the bacterial surface protein InlB with host Met receptor tyrosine kinase. Binding of InlB leads to phosphorylation of Met and the adapter Gab1 and to activation of host phosphoinositide (PI) 3-kinase. The mammalian ligand of Met, hepatocyte growth factor, promotes cell motility and morphogenesis in a manner dependent on phosphorylation of two docking site tyrosines at positions 1349 and 1356 in the receptor's cytoplasmic tail. Here we determined if these tyrosines were essential for
Listeria
entry. A derivative of the human cell line T47D stably expressing a truncated Met lacking most of its cytoplasmic domain was unable to support InlB-mediated signaling or entry. Surprisingly, cells expressing mutant Met containing phenylalanine substitutions in both tyrosines 1349 and 1356 (MetYF) allowed entry and InlB-induced Gab1 phosphorylation. However, in contrast to the situation in cells expressing wild-type Met, Gab1 phosphorylation in MetYF cells required PI 3-kinase activity. The Gab1 pleckstrin homology (PH) domain was constitutively associated with the plasma membrane of cells in a PI 3-kinase-dependent manner. Overexpression of the PH domain blocked entry of
Listeria
into cells expressing MetYF but not into cells expressing wild-type Met. Taken together, these results indicate that the docking site tyrosines are dispensable for internalization when membrane localization of Gab1 is constitutive. Distinct pathways of recruitment by phosphorylated tyrosines in Met and PH domain ligands in the membrane are redundant for bacterial entry.