bluuebunny/crossref_metadata_2025_split huggingface dataset:
ListeriaPathogenesis and Molecular Virulence Determinants
Authors: Vázquez-Boland José A. , Kuhn Michael , Berche Patrick , Chakraborty Trinad , Domı́nguez-Bernal Gustavo , Goebel Werner , González-Zorn Bruno , Wehland Jürgen , Kreft Jürgen 
Published: July 2002

SUMMARYThe gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal indivuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research.
Identification of a Siderophore Receptor Required for Ferric Ornibactin Uptake in
Burkholderia cepacia
Authors: Sokol P. A. , Darling P. , Lewenza S. , Corbett C. R. , Kooi C. D. 
Published: July 2002

ABSTRACT

Ornibactins are linear hydroxamate siderophores produced by
Burkholderia cepacia
with peptide structures similar to that of pyoverdines produced by the fluorescent pseudomonads. The gene encoding the outer membrane receptor (
orbA
) was identified, sequenced, and demonstrated to have significant homology with hydroxamate receptors produced by other organisms. The
orbA
precursor was predicted to be a protein with a molecular mass of 81 kDa. An
orbA
mutant was constructed and demonstrated to be unable to take up
59
Fe-ornibactins or to grow in medium supplemented with ornibactins. Outer membrane protein profiles from the parent strain, K56-2, revealed an iron-regulated outer membrane protein of 78 kDa that was not detectable in the K56
orbA
::tp mutant. When this mutant harbored a plasmid containing the
orbA
gene, the 78-kDa protein was present in the outer membrane protein profiles and the mutant was able to utilize ornibactin to acquire iron. The
orbA
mutant was less virulent in a chronic respiratory infection model than the parent strain, indicating that ornibactin uptake and utilization are important in the pathogenesis of
B. cepacia
respiratory infections.
Antigenicity, Expression, and Molecular Characterization of Surface-Located Pullulanase of
Streptococcus pneumoniae
Authors: Bongaerts Roger J. M. , Heinz Hans-Peter , Hadding Ulrich , Zysk Gregor 
Published: July 2002

ABSTRACT

A putative pullulanase-encoding gene from
Streptococcus pneumoniae
was identified by screening a genomic expression library with human convalescent-phase serum. The 3,864-bp gene encoded a 143-kDa protein. Surface location and pullulanase activity of the protein, designated SpuA, was demonstrated. SpuA was present in all investigated pneumococcal isolates of different serotypes. The
spuA
5′ end was highly conserved among clinical isolates except for a 75-bp region. The properties of SpuA reported here indicate that this novel immunogenic surface protein might have potential as a vaccine target.
Epitope Mapping of Immunogenic and Adhesive Structures in Repetitive Domains of
Mycoplasma bovis
Variable Surface Lipoproteins
Authors: Sachse K. , Helbig J. H. , Lysnyansky I. , Grajetzki C. , Müller W. , Jacobs E. , Yogev D. 
Published: July 2002

ABSTRACT

The family of variable surface lipoproteins (Vsps) of the bovine pathogen
Mycoplasma bovis
includes some of the most immunogenic antigens of this microorganism. Vsps were shown to undergo high-frequency phase and size variations and to possess extensive reiterated coding sequences extending from the N-terminal end to the C-terminal end of the Vsp molecule. In the present study, mapping experiments were conducted to detect regions with immunogenicity and/or adhesion sites in repetitive domains of four Vsp antigens of
M. bovis
, VspA, VspB, VspE, and VspF. In enzyme-linked immunosorbent assay experiments, sera obtained from naturally infected cattle showed antibodies to different repeating peptide units of the Vsps, particularly to units R
A
1, R
A
2, R
A
4.1, R
B
2.1, R
E
1, and R
F
1, all of which were found to contain immunodominant epitopes of three to seven amino acids. Competitive adherence trials revealed that a number of oligopeptides derived from various repeating units of VspA, VspB, VspE, and VspF partially inhibited cytoadhesion of
M. bovis
PG45 to embryonic bovine lung cells. Consequently, putative adherence sites were identified in the same repeating units (R
A
1, R
A
2, R
A
4.1, R
B
2.1, R
E
1, and R
F
1) and in R
F
2. The positions and lengths of the antigenic determinants were mostly identical to those of adhesion-mediating sites in all short repeating units, whereas in the considerably longer R
F
1 unit (84 amino acid residues), there was only one case of identity among four immunogenic epitopes and six adherence sites. The identification of epitopes and adhesive structures in repetitive domains of Vsp molecules is consistent with the highly immunogenic nature observed for several members of the Vsp family and suggests a possible function for these Vsp molecules as complex adherence-mediating regions in pathogenesis.
Relative Roles of Pneumolysin and Hydrogen Peroxide fromStreptococcus pneumoniaein Inhibition of Ependymal Ciliary Beat Frequency
Authors: Hirst Robert A. , Sikand Kulvinder S. , Rutman Andrew , Mitchell Timothy J. , Andrew Peter W. , O'Callaghan Christopher 
Published: July 2002

ABSTRACTCiliated ependymal cells line the ventricular system of the brain and the cerebral aqueducts. This study characterizes the relative roles of pneumolysin and hydrogen peroxide (H2O2) in pneumococcal meningitis, using the in vitro ependymal ciliary beat frequency (CBF) as an indicator of toxicity. We have developed an ex vivo model to examine the ependymal surface of the brain slices cut from the fourth ventricle. The ependymal cells had cilia beating at a frequency of between 38 and 44Hz. D39 (wild-type) and PLN-A (pneumolysin-negative) pneumococci at 108CFU/ml both caused ciliary slowing. Catalase protected against PLN-A-induced ciliary slowing but afforded little protection from D39. Lysed PLN-A did not reduce CBF, whereas lysed D39 caused rapid ciliary stasis. There was no effect of catalase, penicillin, or catalase plus penicillin on the CBF. H2O2at a concentration as low as 100 μM caused ciliary stasis, and this effect was abolished by coincubation with catalase. An additive inhibition of CBF was demonstrated using a combination of both toxins. A significant inhibition of CBF at between 30 and 120 min was demonstrated with both toxins compared with either H2O2(10 μM) or pneumolysin (1 HU/ml) alone. D39 released equivalent levels of H2O2to those released by PLN-A, and these concentrations were sufficient to cause ciliary stasis. The brain slices did not produce H2O2, and in the presence of 108CFU of D39 or PLN-A per ml there was no detectable bacterially induced increase of H2O2release from the brain slice. Coincubation with catalase converted the H2O2produced by the pneumococci to H2O. Penicillin-induced lysis of bacteria dramatically reduced H2O2production. The hemolytic activity released from D39 was sufficient to cause rapid ciliary stasis, and there was no detectable release of hemolytic activity from the pneumolysin-negative PLN-A. These data demonstrate that D39 bacteria released pneumolysin, which caused rapid ciliary stasis. D39 also released H2O2, which contributed to the toxicity, but this was masked by the more severe effects of pneumolysin. H2O2released from intact PLN-A was sufficient to cause rapid ciliary stasis, and catalase protected against H2O2-induced cell toxicity, indicating a role for H2O2in the response. There is also a slight additive effect of pneumolysin and H2O2on ependymal toxicity; however, the precise mechanism of action and the role of these toxins in pathogenesis remain unclear.
Influence of Synthetic Antiendotoxin Peptides on Lipopolysaccharide (LPS) Recognition and LPS-Induced Proinflammatory Cytokine Responses by Cells Expressing Membrane-Bound CD14
Authors: Iwagaki Akitaka , Porro Massimo , Pollack Matthew 
Published: July 2002

ABSTRACTLipopolysaccharides (LPS) are proinflammatory bacterial products implicated in the pathogenesis of gram-negative sepsis and septic shock. Polymyxin B (PMB), a cyclic, cationic peptide antibiotic, inhibits biological activities of LPS through high-affinity binding to the lipid A moiety. Small synthetic peptides have been designed to mimic the primary and secondary structures of PMB to determine structural requirements for binding and detoxification of lipid A and to assess possible therapeutic potential. The purpose of this study was to compare and contrast the endotoxin-neutralizing activities of two synthetic antiendotoxin peptides (SAEP-2 and SAEP-4), PMB, and an LPS core-specific monoclonal antibody (MAb), WN1 222-5, based on their abilities to inhibit CD14-mediated target cell uptake of fluorescein isothiocyanate (FITC)-conjugated LPS, detected by flow cytometry and confocal microscopy, and LPS-induced production of the proinflammatory cytokines, interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α), as measured by bioassays. PMB and SAEP-4 produced dose-dependent inhibition of FITC-LPS uptake by CD14-transfected Chinese hamster ovary fibroblasts (CHO-CD14 cells) and by human peripheral blood mononuclear cells. The anti-LPS MAb, WN1 222-5, also blocked LPS uptake by these cells and synergized with PMB and SAEP-4. LPS-induced IL-6 release was inhibited by PMB, SAEP-4, and MAb WN1 222-5, and these inhibitory activities were additive or synergistic. LPS-induced TNF-α release by PBMC was also inhibited by PMB and SAEP-4 alone and in combination with anti-LPS MAb. SAEP-2, in contrast, produced comparatively minor decrements in cellular uptake of LPS and LPS-induced cytokine responses, and did so only in the absence of serum, while a nonsense peptide exerted no discernible inhibitory effect on LPS uptake or LPS-induced cytokine expression in the presence or absence of serum. Thus, PMB and SAEP-4, like the LPS-reactive MAb, WN1 222-5, block proinflammatory activities of LPS in part by preventing LPS recognition by membrane-bound CD14-expressing target cells. Differences in peptide structure, however, like those exemplified by SAEP-2 and SAEP-4, may differentially affect the endotoxin-neutralizing potency of these peptides despite similar binding activity against lipid A, reflecting possible differences in peptide solubility or peptide regulation of intracellular signal transduction.
Antibody-Mediated Elimination of the Obligate Intracellular Bacterial PathogenEhrlichia chaffeensisduring Active Infection
Authors: Winslow Gary M. , Yager Eric , Shilo Konstantin , Volk Erin , Reilly Andrew , Chu Frederick K. 
Published: July 2002

ABSTRACTIt is generally accepted that cellular, but not humoral immunity, plays an important role in host defense against intracellular bacteria. However, studies of some of these pathogens have provided evidence that antibodies can provide immunity if present during the initiation of infection. Here, we examined immunity against infection byEhrlichia chaffeensis, an obligate intracellular bacterium that causes human monocytic ehrlichiosis. Studies with mice have demonstrated that immunocompetent strains are resistant to persistent infection but that SCID mice become persistently and fatally infected. Transfer of immune serum or antibodies obtained from immunocompetent C57BL/6 mice to C57BL/6scidmice provided significant although transient protection from infection. Bacterial clearance was observed when administration occurred at the time of inoculation or well after infection was established. The effect was dose dependent, occurred within 2 days, and persisted for as long as 2 weeks. Weekly serum administration prolonged the survival of susceptible mice. Although cellular immunity is required for complete bacterial clearance, the data show that antibodies can play a significant role in the elimination of this obligate intracellular bacterium during active infection and thus challenge the paradigm that humoral responses are unimportant for immunity to such organisms.
Enterotoxicity and Cytotoxicity of
Vibrio parahaemolyticus
Thermostable Direct Hemolysin in In Vitro Systems
Authors: Raimondi Francesco , Kao Joseph P. Y. , Fiorentini Carla , Fabbri Alessia , Donelli Gianfranco , Gasparini Nicoletta , Rubino Armido , Fasano Alessio 
Published: July 2002

ABSTRACT

Vibrio parahaemolyticus
is a marine bacterium known to be a common cause of seafood gastroenteritis worldwide. The thermostable direct hemolysin (TDH) has been proposed to be a major virulence factor of
V. parahaemolyticus
. TDH causes intestinal fluid secretion as well as cytotoxicity in a variety of cell types. In this study, we investigated the interplay between the hemolysin's enterotoxic and cytotoxic effects by using both human and rat cell monolayers. As revealed by microspectrofluorimetry, the toxin causes a dose-dependent increase in intracellular free calcium in both Caco-2 and IEC-6 cells. This effect was reversible only when low toxin concentrations were tested. The TDH-activated ion influx pathway is not selective for calcium but admits ions such sodium and manganese as well. Furthermore, in the same range of concentration, the hemolysin triggers a calcium-dependent chloride secretion. At high concentrations, TDH induces a dose-dependent but calcium-independent cell death as assessed by functional, biochemical, and morphological assays.
Evidence of Commonality between Canine and Human Extraintestinal PathogenicEscherichia coliStrains That ExpresspapGAllele III
Authors: Johnson James R. , O'Bryan Timothy T. , Low David A. , Ling Gerald , Delavari Parissa , Fasching Claudine , Russo Thomas A. , Carlino Ulrike , Stell Adam L. 
Published: July 2002

ABSTRACTAlthough dogs have been proposed as carriers of extraintestinal pathogenicEscherichia coli(ExPEC) with infectious potential for humans, presumed host species-specific differences between canine and human ExPEC strains have cast doubt on this hypothesis. The recent discovery that allele III ofpapG(the P fimbrial adhesin gene) predominates among human cystitis isolates and confers an adherence phenotype resembling that of canine ExPEC prompted the present reevaluation of the canine-human ExPEC connection. Sixteen pairedpap-positive urine and rectalE. coliisolates from dogs with urinary tract infection were studied.papG(adhesin) andpapA(pilin) allele type, agglutination phenotypes, virulence factor genotypes, and randomly amplified polymorphic DNA and pulsed-field gel electrophoresis fingerprints were analyzed and compared with those of human ExPEC controls. The 16 canine strains contained predominantlypapGallele III. Agglutination phenotypes segregated strictly according topapGallele status and were homogeneous among strains with the samepapGallele profile irrespective of their human versus canine origin. Canine and human PapG variant III peptide sequences were highly homologous, without host species-specific differences. The most prevalent caninepapAallele was F48, a novel variant recently identified among human urosepsis isolates. In addition topap, human ExPEC-associated virulence genes detected among the canine strains includedsfa/focDE,sfaS,fyuA,hlyA,cnf1,cdtB,kpsMT-II and -III,rfc,traT,ompT, and a marker for a pathogenicity-associated island from archetypal human ExPEC strain CFT073. Molecular fingerprinting confirmed the fecal origin of all but one canine urine isolate and showed one pair of O6 canine urine and fecal isolates to be extremely similar to an O6 human urosepsis isolate with which they shared all other genotypic and phenotypic characteristics analyzed. These data demonstrate that canine ExPEC strains are similar to, and in some instances essentially indistinguishable from, human ExPEC strains, which implicates dogs and their feces as potential reservoirs ofE. coliwith infectious potential for humans.
Interaction of Human Phagocytes with Pigmentless
Aspergillus
Conidia
Authors: Jahn Bernhard , Boukhallouk Fatima , Lotz Johannes , Langfelder Kim , Wanner Gerhard , Brakhage Axel A. 
Published: July 2002

ABSTRACT

A defect in the
pksP
gene of
Aspergillus fumigatus
is associated with the loss of conidial pigmentation, a profound change of the conidial surface structure, and reduced virulence. The structural change of the conidial surface structure was not observed in similar
A. nidulans wA
mutants. Our data indicate that the pigment of both species is important for scavenging reactive oxygen species and for protection of conidia against oxidative damage.
Identification of Genes Required for Chronic Persistence ofBrucella abortusin Mice
Authors: Hong Priscilla C. , Tsolis Renée M. , Ficht Thomas A. 
Published: July 2002

ABSTRACTThe genetic basis for chronic persistence ofBrucella abortusin lymphoid organs of mice, cows, and humans is currently unknown. We identifiedB. abortusgenes involved in chronic infection, by assessing the ability of 178 signature-tagged mutants to establish and maintain persistent infection in mice. Each mutant was screened for its ability to colonize the spleens of mice at 2 and 8 weeks after inoculation. Comparison of the results from both time points identified two groups of mutants attenuated for chronic infection in mice. The first group was not recovered at either 2 or 8 weeks postinfection and was therefore defective in establishing infection. Mutants in this group carried transposon insertions in genes involved in lipopolysaccharide biosynthesis (wbkA), in aromatic amino acid biosynthesis, and in type IV secretion (virB1andvirB10). The second group, which was recovered at wild-type levels 2 weeks postinfection but not 8 weeks postinfection was able to establish infection but was unable to maintain chronic infection. One mutant in this group carried a transposon insertion in a gene with homology togcvBofMycobacterium tuberculosis, encoding glycine dehydrogenase, an enzyme whose activity is increased during the state of nonreplicating persistence. These results suggest that some mechanisms for long-term persistence may be shared among chronic intracellular pathogens. Furthermore, identification of two groups of genes, those required for initiating infection and those required only for long-term persistence, suggests thatB. abortususes distinct sets of virulence determinants to establish and maintain chronic infection in mice.
Differential Modulation and Subsequent Blockade of Mitogenic Signaling and Cell Cycle Progression byPasteurella multocidaToxin
Authors: Wilson Brenda A. , Aminova Lyaylya R. , Ponferrada Virgilio G. , Ho Mengfei 
Published: July 2002

ABSTRACTThe intracellularly acting protein toxin ofPasteurella multocida(PMT) causes numerous effects in cells, including activation of inositol 1,4,5-trisphosphate (IP3) signaling, Ca2+mobilization, protein phosphorylation, morphological changes, and DNA synthesis. The direct intracellular target of PMT responsible for activation of the IP3pathway is the Gq/11α-protein, which stimulates phospholipase C (PLC) β1. The relationship between PMT-mediated activation of the Gq/11-PLC-IP3pathway and its ability to promote mitogenesis and cellular proliferation is not clear. PMT stimulation of p42/p44 mitogen-activated protein kinase occurs upstream via Gq/11-dependent transactivation of the epidermal growth factor receptor. We have further characterized the effects of PMT on the downstream mitogenic response and cell cycle progression in Swiss 3T3 and Vero cells. PMT treatment caused dramatic morphological changes in both cell lines. In Vero cells, limited multinucleation, nuclear fragmentation, and disruption of cytokinesis were also observed; however, a strong mitogenic response occurred only with Swiss 3T3 cells. Significantly, this mitogenic response was not sustained. Cell cycle analysis revealed that after the initial mitogenic response to PMT, both cell types subsequently arrested primarily in G1and became unresponsive to further PMT treatment. In Swiss 3T3 cells, PMT induced up-regulation of c-Myc; cyclins D1, D2, D3, and E; p21; PCNA; and the Rb proteins, p107 and p130. In Vero cells, PMT failed to up-regulate PCNA and cyclins D3 and E. We also found that the initial PMT-mediated up-regulation of several of these signaling proteins was not sustained, supporting the subsequent cell cycle arrest. The consequences of PMT entry thus depend on the differential regulation of signaling pathways within different cell types.
[Cu,Zn]-Superoxide Dismutase Mutants of the Swine PathogenActinobacillus pleuropneumoniaeAre Unattenuated in Infections of the Natural Host
Authors: Sheehan Brian J. , Langford Paul R. , Rycroft Andrew N. , Kroll J. Simon 
Published: July 2002

ABSTRACTActinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, contains a periplasmic Cu- and Zn-cofactored superoxide dismutase ([Cu,Zn]-SOD, or SodC) which has the potential, realized in other pathogens, to promote bacterial survival during infection by dismutating host-defense-derived superoxide. Here we describe the construction of a site-specific, [Cu,Zn]-SOD-deficientA. pleuropneumoniaeserotype 1 mutant and show that although the mutant is highly sensitive to the microbicidal action of superoxide in vitro, it remains fully virulent in experimental pulmonary infection in pigs.