bluuebunny/crossref_metadata_2025_split huggingface dataset:
TheSalmonella entericaSerovar TyphitsxGene, Encoding a Nucleoside-Specific Porin, Is Essential for Prototrophic Growth in the Absence of Nucleosides
Authors: Bucarey Sergio A. , Villagra Nicolás A. , Martinic Mara P. , Trombert A. Nicole , Santiviago Carlos A. , Maulén Nancy P. , Youderian Philip , Mora Guido C. 
Published: September 2005

ABSTRACTTheSalmonella entericaserovar Typhitsxgene encodes a porin that facilitates the import of nucleosides. When serovar Typhi is grown under anaerobic conditions, Tsx is among the outer membrane proteins whose expression increases dramatically. This increase in expression is due, at least in part, to increased transcription and is dependent on Fnr but not on ArcA. A mutant derivative of serovar Typhi strain STH2370 with a deletion of thetsxgene is an auxotroph that requires either adenosine or thymidine for growth on minimal medium. In contrast, an otherwise isogenicnupG nupCdouble mutant, defective in the inner membrane nucleoside permeases, is a prototroph. Because anaerobic growth enhances the virulence of serovar Typhi in vitro, we assessed the role that thetsxgene plays in pathogenicity and found that the serovar Typhi STH2370 Δtsxmutant is defective in survival within human macrophage-like U937 cells. To understand why the Δtsxmutant is an auxotroph, we selected for insertions of minitransposon T-POP in the Δtsxgenetic background that restored prototrophy. One T-POP insertion that suppressed the Δtsxmutation in the presence of the inducer tetracycline was located upstream of thepyrDgene. The results of reverse transcription-PCR analysis showed that addition of the inducer decreased the rate ofpyrDtranscription. These results suggest that the Tsx porin and the balance of products of thetsxandpyrDgenes play critical roles in membrane assembly and integrity and thus in the virulence of serovar Typhi.
Major Histocompatibility Complex Class II Inhibits Fas Antigen-Mediated Gastric Mucosal Cell Apoptosis through Actin-Dependent Inhibition of Receptor Aggregation
Authors: Stoicov Calin , Cai Xun , Li Hanchen , Klucevsek Kristine , Carlson Jane , Saffari Reza , Houghton JeanMarie 
Published: September 2005

ABSTRACTEscape from normal apoptotic controls is thought to be essential for the development of cancer. DuringHelicobacter pyloriinfection, the leading cause of gastric cancer, activation of the Fas antigen (Fas Ag) apoptotic pathway is responsible for early atrophy and tissue loss. As disease progresses, metaplastic and dysplastic glands arise which express Fas Ag but are resistant to apoptosis and are believed to be the precursor cells for adenocarcinoma. In this report, we show that one mechanism of acquired Fas resistance is inhibition of receptor aggregation via a major histocompatibility complex class II (MHCII)-mediated, actin-dependent mechanism. For these studies we used the well-described C57BL/6 mouse model ofHelicobacter pyloriandHelicobacter felisinfection. Under normal conditions, Fas Ag is expressed at low levels, and MHCII expression on gastric mucosal cells is negligible. With infection and inflammation, both receptors are upregulated, and 6.1% of gastric mucosal cells express MHCII in combination with Fas Ag. Using the rat gastric mucosal cell line RGM-1 transfected with murine Fas Ag and MHCIIαβ chains, we demonstrate that MHCII prevents Fas receptor aggregation and inhibits Fas-mediated signaling through its effects on the actin cytoskeleton. Depolymerization of actin with cytochalasin D allows receptors to aggregate and restores Fas sensitivity. These findings offer one mechanism by which gastric mucosal cells acquire Fas resistance.
Conserved Structure and Function in the Granulysin and NK-Lysin Peptide Family
Authors: Linde Charlotte M. A. , Grundström Susanna , Nordling Erik , Refai Essam , Brennan Patrick J. , Andersson Mats 
Published: September 2005

ABSTRACTGranulysin and NK-lysin are homologous bactericidal proteins with a moderate residue identity (35%), both of which have antimycobacterial activity. Short loop peptides derived from the antimycobacterial domains of granulysin, NK-lysin, and a putative chicken NK-lysin were examined and shown to have comparable antimycobacterial but variableEscherichia coliactivities. The known structure of the NK-lysin loop peptide was used to predict the structure of the equivalent peptides of granulysin and chicken NK-lysin by homology modeling. The last two adopted a secondary structure almost identical to that of NK-lysin. All three peptides form very similar three-dimensional (3-D) architectures in which the important basic residues assume the same positions in space. The basic residues in granulysin are arginine, while those in NK-lysin and chicken NK-lysin are a mixture of arginine and lysine. We altered the ratio of arginine to lysine in the granulysin fragment to examine the importance of basic residues for antimycobacterial activity. The alteration of the amino acids reduced the activity againstE. colito a larger extent than that againstMycobacterium smegmatis. In granulysin, the arginines in the loop structure are not crucial for antimycobacterial activity but are important for cytotoxicity. We suggest that the antibacterial domains of the related proteins granulysin, NK-lysin, and chicken NK-lysin have conserved their 3-D structure and their function against mycobacteria.
Specific Antibody Can Prevent Fungal Biofilm Formation and This Effect Correlates with Protective Efficacy
Authors: Martinez Luis R. , Casadevall Arturo 
Published: September 2005

ABSTRACT

One of the most troublesome medical problems today is infection of prosthetic devices with organisms that form polysaccharide biofilms. This combined with increasing antimicrobial drug resistance is making many infectious diseases incurable.
Cryptococcus neoformans
is a human-pathogenic fungus that has a polysaccharide capsule and can form biofilms in prosthetic medical devices. We developed a system to study cryptococcal biofilm formation in vitro and studied the effect of antibody to the
C. neoformans
capsular polysaccharide on this process.
C. neoformans
biofilm formation was dependent on the presence of a polysaccharide capsule and correlated with the ability of capsular polysaccharide to bind the polystyrene solid support. Protective antibodies prevented biofilm formation whereas nonprotective antibodies were not effective. The mechanism of antibody action involved interference with capsular polysaccharide release from the fungal cell. In contrast, lactoferrin, an effector molecule of innate immune mechanisms, was unable to prevent fungal biofilm formation despite its efficacy against bacterial biofilms. Our results suggest a new role of adaptive humoral immunity whereby some antibodies can inhibit biofilm formation by encapsulated organisms. Vaccines that elicit antibody responses to capsular antigens and/or passive transfer of antibodies to microbial polysaccharides may be useful in preventing biofilm formation.
The Type III Secretion System and Cytotoxic Enterotoxin Alter the Virulence of
Aeromonas hydrophila
Authors: Sha Jian , Pillai Lakshmi , Fadl Amin A. , Galindo Cristi L. , Erova Tatiana E. , Chopra Ashok K. 
Published: September 2005

ABSTRACT

Many gram-negative bacteria use a type III secretion system (TTSS) to deliver effector proteins into host cells. Here we report the characterization of a TTSS chromosomal operon from the diarrheal isolate SSU of
Aeromonas hydrophila
. We deleted the gene encoding
Aeromonas
outer membrane protein B (AopB), which is predicted to be involved in the formation of the TTSS translocon, from wild-type (WT)
A. hydrophila
as well as from a previously characterized cytotoxic enterotoxin gene (
act
)-minus strain of
A. hydrophila
, thus generating
aopB
and
act/aopB
isogenic mutants. The
act
gene encodes a type II-secreted cytotoxic enterotoxin (Act) that has hemolytic, cytotoxic, and enterotoxic activities and induces lethality in a mouse model. These isogenic mutants (
aopB
,
act
, and
act/aopB
) were highly attenuated in their ability to induce cytotoxicity in RAW 264.7 murine macrophages and HT-29 human colonic epithelial cells. The
act/aopB
mutant demonstrated the greatest reduction in cytotoxicity to cultured cells after 4 h of infection, as measured by the release of lactate dehydrogenase enzyme, and was avirulent in mice, with a 90% survival rate compared to that of animals infected with Act and AopB mutants, which caused 50 to 60% of the animals to die at a dose of three 50% lethal doses. In contrast, WT
A. hydrophila
killed 100% of the mice within 48 h. The effects of these mutations on cytotoxicity could be complemented with the native genes. Our studies further revealed that the production of lactones, which are involved in quorum sensing (QS), was decreased in the
act
(32%) and
aopB
(64%) mutants and was minimal (only 8%) in the
act/aopB
mutant, compared to that of WT
A. hydrophila
SSU. The effects of
act
and
aopB
gene deletions on lactone production could also be complemented with the native genes, indicating specific effects of Act and the TTSS on lactone production. Although recent studies with other bacteria have indicated TTSS regulation by QS, this is the first report describing a correlation between the TTSS and Act of
A. hydrophila
and the production of lactones.
Effects of RepeatedChlamydia pneumoniaeInoculations on Aortic Lipid Accumulation and Inflammatory Response in C57BL/6J Mice
Authors: Törmäkangas Liisa , Erkkilä Leena , Korhonen Taina , Tiirola Terttu , Bloigu Aini , Saikku Pekka , Leinonen Maija 
Published: September 2005

ABSTRACTChlamydia pneumoniaeis a common respiratory tract pathogen, and persistent infections have been associated with atherosclerosis. We studied the effects of repeated chlamydial inoculations on the inflammatory response and on aortic lipid accumulation in C57BL/6J mice. Mice fed a diet supplemented with 0.2% cholesterol were infected three or six times withC. pneumoniaeevery fourth week. Sera and lungs were analyzed for inflammatory responses, lung tissues were tested for the presence ofC. pneumoniaeDNA and RNA, and intimal lipid accumulation in the aortic sinus was quantified. High levels of chlamydial heat shock protein 60 (Hsp60) immunoglobulin G2c subclass antibodies were detected in all of the infected mice, and a positive and statistically significant correlation was found between these antibodies and autoantibodies against mouse Hsp60. Both Hsp60 antibody levels correlated with the severity of lung tissue inflammation. The cholesterol supplement in the diet had no effect on serum cholesterol levels. Significantly larger intimal lipid lesions were seen in the mouse group infected six times (6,542 μm2) than in the control group (1,376 μm2;P= 0.034). In conclusion, repeated inoculations increased aortic sinus lipid accumulation in normocholesterolemic mice. The correlation between the antibodies to mouse and chlamydial Hsp60 proteins and their association with lung inflammation further support the theory of the development of an autoimmune response against heat shock proteins after repeated chlamydial infections.
The Apoptotic Response to Pneumolysin Is Toll-Like Receptor 4 Dependent and Protects against Pneumococcal Disease
Authors: Srivastava Amit , Henneke Philipp , Visintin Alberto , Morse Sarah C. , Martin Victoria , Watkins Claire , Paton James C. , Wessels Michael R. , Golenbock Douglas T. , Malley Richard 
Published: September 2005

ABSTRACTPneumolysin, the cholesterol-dependent cytolysin ofStreptococcus pneumoniae, induces inflammatory and apoptotic events in mammalian cells. Toll-like receptor 4 (TLR4) confers resistance to pneumococcal infection via its interaction with pneumolysin, but the underlying mechanisms remain to be identified. In the present study, we found that pneumolysin-induced apoptosis is also mediated by TLR4 and confers protection against invasive disease. The interaction between TLR4 and pneumolysin is direct and specific; ligand-binding studies demonstrated that pneumolysin binds to TLR4 but not to TLR2. Involvement of TLR4 in pneumolysin-induced apoptosis was demonstrated in several complementary experiments. First, macrophages from wild-type mice were significantly more prone to pneumolysin-induced apoptosis than cells from TLR4-defective mice. In gain-of-function experiments, we found that epithelial cells expressing TLR4 and stimulated with pneumolysin were more likely to undergo apoptosis than cells expressing TLR2. A specific TLR4 antagonist, B1287, reduced pneumolysin-mediated apoptosis in wild-type cells. This apoptotic response was also partially caspase dependent as preincubation of cells with the pan-caspase inhibitor zVAD-fmk reduced pneumolysin-induced apoptosis. Finally, in a mouse model of pneumococcal infection, pneumolysin-producing pneumococci elicited significantly more upper respiratory tract cell apoptosis in wild-type mice than in TLR4-defective mice, and blocking apoptosis by administration of zVAD-fmk to wild-type mice resulted in a significant increase in mortality following nasopharyngeal pneumococcal exposure. Overall, our results strongly suggest that protection against pneumococcal disease is dependent on the TLR4-mediated enhancement of pneumolysin-induced apoptosis.
Clearance ofBordetella parapertussisfrom the Lower Respiratory Tract Requires Humoral and Cellular Immunity
Authors: Wolfe Daniel N. , Kirimanjeswara Girish S. , Harvill Eric T. 
Published: September 2005

ABSTRACTBordetella parapertussisandBordetella pertussisare closely related species that cause whooping cough, an acute, immunizing disease. Their coexistence in the same host populations at the same time and vaccine studies showing thatB. pertussisvaccines have little effect onB. parapertussisinfection or disease suggest that the protective immunity induced by each does not efficiently cross protect against the other. Although the mechanisms of protective immunity toB. pertussishave been well studied, those ofB. parapertussishave not. The present study explores the mechanism by whichB. parapertussisis cleared from the lower respiratory tract by anamnestic immunity. Serum antibodies are necessary and sufficient for elimination of this bacterium, and CD4+T cells, complement, and neutrophils are required for serum antibody-mediated clearance. Mice lacking immunoglobulin A had no defect in their ability to control or clear infection. Interestingly, serum antibody-mediated clearance ofB. parapertussisdid not require Fc receptors that are required for antibody-mediated clearance ofB. pertussis. Together these data support a model for the mechanism of protective immunity toB. parapertussisthat is similar but distinct from that ofB. pertussis.
Recombinant Shiga Toxin B-Subunit-Keyhole Limpet Hemocyanin Conjugate Vaccine Protects Mice from Shigatoxemia
Authors: Marcato Paola , Griener Thomas P. , Mulvey George L. , Armstrong Glen D. 
Published: September 2005

ABSTRACT

Enterohemorrhagic
Escherichia coli
(EHEC) causes hemorrhagic colitis in humans and, in a subgroup of infected subjects, a more serious condition called hemolytic-uremic syndrome (HUS). These conditions arise because EHEC produces two antigenically distinct forms of Shiga toxin (Stx), called Stx1 and Stx2. Despite this, the production of Stx2 by virtually all EHEC serotypes and the documented role this toxin plays in HUS make it an attractive vaccine candidate. Previously, we assessed the potential of a purified recombinant Stx2 B-subunit preparation to prevent Shigatoxemia in rabbits. This study revealed that effective immunization could be achieved only if endotoxin was included with the vaccine antigen. Since the presence of endotoxin would be unacceptable in a human vaccine, the object of the studies described herein was to investigate ways to safely augment, in mice, the immunogenicity of the recombinant Stx2 B subunit containing <1 endotoxin unit per ml. The study revealed that sera from mice immunized with such a preparation, conjugated to keyhole limpet hemocyanin and administered with the Ribi adjuvant system, displayed the highest Shiga toxin 2 B-subunit-specific immunoglobulin G1 (IgG1) and IgG2a enzyme-linked immunosorbent assay titers and cytotoxicity-neutralizing activities in Ramos B cells. As well, 100% of the mice vaccinated with this preparation were subsequently protected from a lethal dose of Stx2 holotoxin. These results support further evaluation of a Stx2 B-subunit-based human EHEC vaccine.
A DNA Vaccine Coding for theBrucellaOuter Membrane Protein 31 Confers Protection againstB. melitensisandB. ovisInfection by Eliciting a Specific Cytotoxic Response
Authors: Cassataro Juliana , Velikovsky Carlos A. , de la Barrera Silvia , Estein Silvia M. , Bruno Laura , Bowden Raúl , Pasquevich Karina A. , Fossati Carlos A. , Giambartolomei Guillermo H. 
Published: September 2005

ABSTRACTThe development of an effective subunit vaccine against brucellosis is a research area of intense interest. The outer membrane proteins (Omps) ofBrucellaspp. have been extensively characterized as potential immunogenic and protective antigens. This study was conducted to evaluate the immunogenicity and protective efficacy of theB. melitensisOmp31 gene cloned in the pCI plasmid (pCIOmp31). Immunization of BALB/c mice with pCIOmp31 conferred protection againstB. ovisandB. melitensisinfection. Mice vaccinated with pCIOmp31 developed a very weak humoral response, and in vitro stimulation of their splenocytes with recombinant Omp31 did not induced the secretion of gamma interferon. Splenocytes from Omp31-vaccinated animals induced a specific cytotoxic-T-lymphocyte activity, which leads to the in vitro lysis ofBrucella-infected macrophages. pCIOmp31 immunization elicited mainly CD8+T cells, which mediate cytotoxicity via perforins, but also CD4+T cells, which mediate lysis via the Fas-FasL pathway. In vivo depletion of T-cell subsets showed that the pCIOmp31-induced protection againstBrucellainfection is mediated predominantly by CD8+T cells, although CD4+T cells also contribute. Our results demonstrate that the Omp31 DNA vaccine induces cytotoxic responses that have the potential to contribute to protection againstBrucellainfection. The protective response could be related to the induction of CD8+T cells that eliminateBrucella-infected cells via the perforin pathway.
Reduction in Capsular Content and Enhanced Bacterial Susceptibility to Serum Killing of
Vibrio cholerae
O139 Associated with the 2002 Cholera Epidemic in Bangladesh
Authors: Qadri Firdausi , Svennerholm Ann-Mari , Shamsuzzaman Sohel , Bhuiyan Taufiqur Rahman , Harris Jason B. , Ghosh A. N. , Nair G. Balakrish , Weintraub Andrej , Faruque Shah M. , Ryan Edward T. , Sack David A. , Calderwood Stephen B. 
Published: September 2005

ABSTRACT

Vibrio cholerae
O139 emerged in 1992 as a major cause of epidemic cholera. However, the incidence of disease due to this new serogroup subsequently decreased for almost a decade. In April 2002, there was a dramatic resurgence of
V. cholerae
O139 in Bangladesh. We compared the phenotypic properties of the bacterial isolates and the immunological responses in patients with disease due to
V. cholerae
O139 during the 2002 epidemic with those dating to the emergence of this disease in 1993 to 1995. Strains isolated from patients in the two time periods were compared with respect to capsular polysaccharide, their resistance to the bactericidal effect of serum, and their capacity to be used as target strains in complement-mediated vibriocidal assays. Phase-contrast microscopy showed that strains isolated in 2002 had less capsular material than those isolated from 1993 to 1995 (
P
= <0.001), a finding confirmed by electron microscopic studies. Strains isolated in 2002 were more susceptible to the bactericidal activity of serum compared to strains from 1993 to 1995 (
P
= 0.013). Compared to results using a standard O139 strain, a modified vibriocidal assay utilizing a 2002 strain, CIRS 134, as the target organism detected higher vibriocidal responses in both O139-infected cholera patients as well as O139 vaccine recipients. The vibriocidal assay utilizing the less encapsulated 2002 strain, CIRS 134, is a more sensitive indicator of adaptive immune responses to recent infection with
V. cholerae
O139. Consequently, this assay may be useful in studies of both O139-infected patients and recipients of O139 vaccines.
Characterization ofListeria monocytogenesExpressing Anthrolysin O and Phosphatidylinositol-Specific Phospholipase C fromBacillus anthracis
Authors: Wei Zhengyu , Schnupf Pamela , Poussin Mathilde A. , Zenewicz Lauren A. , Shen Hao , Goldfine Howard 
Published: September 2005

ABSTRACTTwo virulence factors ofListeria monocytogenes, listeriolysin O (LLO) and phosphatidylinositol-specific phospholipase C (PI-PLC), mediate escape of this pathogen from the phagocytic vacuole of macrophages, thereby allowing the bacterium access to the host cell cytosol for growth and spread to neighboring cells. We characterized their orthologs fromBacillus anthracisby expressing them inL. monocytogenesand characterizing their contribution to bacterial intracellular growth and cell-to-cell spread. We generated a series ofL. monocytogenesstrains expressingB. anthracisanthrolysin O (ALO) and PI-PLC in place of LLO andL. monocytogenesPI-PLC, respectively. We found that ALO was active at both acidic and neutral pH and could functionally replace LLO in mediating escape from a primary vacuole; however, ALO exerted a toxic effect on the host cell by damaging the plasma membrane.B. anthracisPI-PLC, unlike theL. monocytogenesortholog, had high activity on glycosylphosphatidylinositol-anchored proteins.L. monocytogenesexpressingB. anthracisPI-PLC showed significantly decreased efficiencies of escape from a phagosome and in cell-to-cell spread. We further compared the level of cytotoxicity to host cells by using mutant strains expressing ALO in combination either withL. monocytogenesPI-PLC or withB. anthracisPI-PLC. The results demonstrated that the mutant strain expressing the combination of ALO andB. anthracisPI-PLC caused less damage to host cells than the strain expressing ALO andL. monocytogenesPI-PLC. The present study indicates that LLO andL. monocytogenesPI-PLC has adapted forL. monocytogenesintracellular growth and virulence and suggests that ALO andB. anthracisPI-PLC may have a role inB. anthracispathogenesis.