bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contribution of the Twin Arginine Translocation System to the Virulence of Enterohemorrhagic
Escherichia coli
O157:H7
Authors: Pradel Nathalie , Ye Changyun , Livrelli Valérie , Xu Jianguo , Joly Bernard , Wu Long-Fei 
Published: August 2003

ABSTRACT

Shiga toxin-producing
Escherichia coli
O157:H7 is a major food-borne infectious pathogen. In order to analyze the contribution of the twin arginine translocation (TAT) system to the virulence of
E. coli
O157:H7, we deleted the
tatABC
genes of the O157:H7 EDL933 reference strain. The mutant displayed attenuated toxicity on Vero cells and completely lost motility on soft agar plates. Further analyses revealed that the Δ
tatABC
mutation impaired the secretion of the Shiga toxin 1 (Stx1) and abolished the synthesis of H7 flagellin, which are two major known virulence factors of enterohemorrhagic
E. coli
O157:H7. Expression of the EDL933
stxAB
1
genes in
E. coli
K-12 conferred verotoxicity on this nonpathogenic strain. Remarkably, cytotoxicity assay and immunoblot analysis showed, for the first time, an accumulation of the holotoxin complex in the periplasm of the wild-type strain and that a much smaller amount of StxA
1
and reduced verotoxicity were detected in the Δ
tatC
mutant cells. Together, these results establish that the TAT system of
E. coli
O157:H7 is an important virulence determinant of this enterohemorrhagic pathogen.
Mice Lacking Inducible Nitric Oxide Synthase Demonstrate Impaired Killing of
Porphyromonas gingivalis
Authors: Gyurko Robert , Boustany Gabriel , Huang Paul L. , Kantarci Alpdogan , Van Dyke Thomas E. , Genco Caroline A. , Gibson Frank C. 
Published: August 2003

ABSTRACT

Porphyromonas gingivalis
is a primary etiological agent of generalized severe periodontitis, and emerging data suggest the importance of reactive oxygen and nitrogen species in periodontal tissue damage, as well as in microbial killing. Since nitric oxide (NO) released from inducible NO synthase (iNOS) has been shown to possess immunomodulatory, cytotoxic, and antibacterial effects in experimental models, we challenged iNOS-deficient (iNOS
−/−
) mice with
P. gingivalis
by using a subcutaneous chamber model to study the specific contribution of NO to host defense during
P. gingivalis
infection. iNOS
−/−
mice inoculated with
P. gingivalis
developed skin lesions and chamber rejection with higher frequency and to a greater degree than similarly challenged C57BL/6 wild-type (WT) mice. Chamber fluid from iNOS
−/−
mice possessed significantly more
P. gingivalis
than that of WT mice. The immunoglobulin G responses to
P. gingivalis
in serum was similar in WT and iNOS
−/−
mice, and the inductions of tumor necrosis factor alpha, interleukin-1β and interleukin-6, and prostaglandin E
2
were comparable between the two mouse strains. Although no differences in total leukocyte counts in chamber fluids were observed between iNOS
−/−
and WT mice, the percentage of dead polymorphonuclear leukocytes (PMNs) was significantly greater in iNOS
−/−
mouse chamber fluids than that of WT samples. Interestingly, casein-elicited PMNs from iNOS
−/−
mice released more superoxide than did WT PMNs when stimulated with
P. gingivalis
. These results indicate that modulation of superoxide levels is a mechanism by which NO influences PMN function and that NO is an important element of the host defense against
P. gingivalis
.
ZmpB, a Novel Virulence Factor ofStreptococcus pneumoniaeThat Induces Tumor Necrosis Factor Alpha Production in the Respiratory Tract
Authors: Blue C. E. , Paterson G. K. , Kerr A. R. , Bergé M. , Claverys J. P. , Mitchell T. J. 
Published: August 2003

ABSTRACTInflammation is a prominent feature ofStreptococcus pneumoniaeinfection in both humans and animal models. Indeed, an intense host immune response to infection is thought to contribute significantly to the pathology of pneumococcal pneumonia and meningitis. Previously, induction of the inflammatory response following infection withS. pneumoniaehas been attributed to certain cell wall constituents and the toxin pneumolysin. Here we present data implicating a putative zinc metalloprotease, ZmpB, as having a role in inflammation. Null mutations were created in thezmpBgene of the virulent serotype 2 strain D39 and analyzed in a murine model of infection. Isogenic mutants were attenuated in pneumonia and septicemia models of infection, as determined by levels of bacteremia and murine survival. Mutants were not attenuated in colonization of murine airways or lung tissue. Examination of cytokine profiles within the lung tissue revealed significantly lower levels of the proinflammatory cytokine tumor necrosis factor alpha following challenge with theΔzmpBmutant (Δ739). These data identify ZmpB as a novel virulence factor capable of inducing inflammation in the lower respiratory tract. The possibility that ZmpB was involved in inhibition of complement activity was examined, but the data indicated that ZmpB does not have a significant effect on this important host defense. The regulation of ZmpB by a two-component system (TCS09) located immediately upstream of thezmpBgene was examined. TCS09 was not required for the expression ofzmpBduring exponential growth in vitro.
Bordetella pertussisAcquires Resistance to Complement-Mediated Killing In Vivo
Authors: Pishko Elizabeth J. , Betting David J. , Hutter Christina S. , Harvill Eric T. 
Published: August 2003

ABSTRACTIn order to initially colonize a host, bacteria must avoid various components of the innate immune system, one of which is complement. The genusBordetellaincludes three closely related species that differ in their ability to resist complement-mediated killing.Bordetella parapertussisandBordetella bronchisepticaresist killing in naïve serum, a characteristic that may aid in efficient respiratory tract colonization and has been attributed to expression of O antigen.Bordetella pertussislacks O antigen and is sensitive to naïve serum in vitro, yet it also efficiently colonizes the respiratory tract. Based on these observations, we hypothesized thatB. pertussismay have an alternate mechanism to resist complement in vivo. While a number of reports on serum sensitivity of the bordetellae have been published, we show here that serum concentration and growth conditions can greatly alter the observed level of sensitivity to complement and that all but one strain ofB. pertussisobserved were sensitive to some level of naïve serum in vitro, particularly when there was excess complement. However,B. pertussisrapidly acquires increased resistance in vivo to naïve serum that is specific to the alternative pathway. Resistance is not efficiently acquired byB. parapertussisandB. bronchisepticamutants lacking O antigen. ThisB. pertussis-specific mechanism of complement resistance does not appear to be dependent on eitherbrkAor other genes expressed specifically in the Bvg+phase. This in vivo acquisition of alternative pathway resistance suggests that there is a novel O antigen-independent method by whichB. pertussisevades complement-mediated killing.
Skin Facilitates
Candida albicans
Mating
Authors: Lachke Salil A. , Lockhart Shawn R. , Daniels Karla J. , Soll David R. 
Published: August 2003

ABSTRACT

Mating between natural
a/a
and α/α strains of
Candida albicans
requires that cells first switch from the white to opaque phase phenotype. However, because cells expressing the opaque phase phenotype are induced to switch back to the white phase phenotype at physiological temperature (37°C) and because opaque phase cells are highly efficient at colonizing skin, we tested whether skin, which is several degrees lower than physiological temperature, is conducive to mating. Using a model in which a mixture of
a/a
and α/α cells are incubated for 24 h under a cotton patch on the hairless skin of newborn mice and using scanning electron microscopy to visualize cells on skin, it was demonstrated that skin facilitates mating. In some regions of the skin, 40% of all cells had fused. All of the stages of mating observed in vitro were observed in vivo. However, some unique morphological characteristics of mating on skin were observed and are attributable to parent cell immobilization on the skin. In control experiments on glass, plastic, and silicone elastomer surfaces at 32°C, cells either failed to fuse or did so at an extremely low frequency, suggesting that unique features of the skin surface other than reduced temperature also facilitate fusion.
The Hag Protein ofMoraxella catarrhalisStrain O35E Is Associated with Adherence to Human Lung and Middle Ear Cells
Authors: Holm Melissa M. , Vanlerberg Serena L. , Sledjeski Darren D. , Lafontaine Eric R. 
Published: August 2003

ABSTRACTPrevious studies have demonstrated that theMoraxella catarrhalissurface antigen UspA1 is an adhesin for Chang human conjunctival cells. The present report demonstrates that lack of UspA1 expression does not affect the adherence of strain O35E to A549 human lung cells or primary cultures of human middle ear epithelial (HMEE) cells. These results imply that another molecule mediates the adherence ofM. catarrhalisto these two cell lines. To identify this adhesin, strain O35E was mutagenized with a transposon and 1,000 mutants were screened in a microcolony formation assay using A549 cells. Nine independent isolates exhibited an 8- to 19-fold reduction in adherence and contained a transposon in the same locus. Nucleotide sequence data and PCR analysis indicated that the transposons were inserted in different locations in the gene encoding the surface protein Hag. Quantitative assays using one representative transposon mutant, O35E.TN2, showed considerably decreased binding to A549 as well as HMEE cells. However, this mutant adhered at wild-type levels to Chang conjunctival cells. These findings suggest that theM. catarrhalisHag protein is an adhesin for cell lines derived from human lung and middle ear tissues.
Multiple Elements Controlling Adherence of Enterohemorrhagic
Escherichia coli
O157:H7 to HeLa Cells
Authors: Torres Alfredo G. , Kaper James B. 
Published: August 2003

ABSTRACT

Adherence of enterohemorrhagic
Escherichia coli
(EHEC) to the intestinal epithelium is essential for initiation of infection. Intimin is the only factor demonstrated to play a role in intestinal colonization by EHEC O157:H7. Other attempts to identify additional adhesion factors in vitro have been unsuccessful, suggesting that expression of these factors is under tight regulation. We sought to identify genes involved in the control of adherence of EHEC O157:H7 to cultured epithelial cells. A total of 5,000 independent transposon insertion mutants were screened for their ability to adhere to HeLa cells, and 7 mutants were isolated with a markedly enhanced adherence. The mutants adhered at levels 113 to 170% that of the wild-type strain, and analysis of the protein profiles of these mutants revealed several proteins differentially expressed under in vitro culture conditions. We determined the sequence of the differentially expressed proteins and further investigated the function of OmpA, whose expression was increased in a mutant with an insertionally inactivated
tcdA
gene. An isogenic
ompA
mutant showed reduced adherence compared to the parent strain. Disruption of the
ompA
gene in the
tdcA
mutant strain abolished the hyperadherent phenotype, and anti-OmpA serum inhibited adhesion of wild-type and
tdcA
mutant strains to HeLa cells. Enhanced adhesion mediated by OmpA was also observed with Caco-2 cells, and anti-OmpA serum blocked adherence to HeLa cells of other EHEC O157:H7 strains. Our results indicate that multiple elements control adherence and OmpA acts as an adhesin in EHEC O157:H7.
Schistosomiasis Decreases Central Nervous System Inflammation and Alters the Progression of Experimental Autoimmune Encephalomyelitis
Authors: La Flamme Anne Camille , Ruddenklau Kate , Bäckström B. Thomas 
Published: August 2003

ABSTRACTA preestablished infection with the parasitic helminth,Schistosoma mansoni, significantly reduced the incidence and delayed the onset of experimental autoimmune encephalomyelitis (EAE) in C57BL/6J mice immunized with myelin oligodendrocyte glycoprotein (MOG)35-55peptide. The altered disease progression was not solely due to the induction of a strong Th2 response, since intraperitoneal injection of schistosome eggs did not affect disease development. MOG-specific gamma interferon (IFN-γ), nitric oxide, and tumor necrosis factor alpha production by splenocytes was significantly reduced in schistosome-infected mice compared to uninfected mice. However, similar levels of interleukin-10 (IL-10) were produced in an antigen-specific manner, suggesting that the induction of antigen-specific responses was not inhibited. Analysis of in vivo cytokine production by real-time PCR indicated that IL-12p40, but not IFN-γ, transcript levels were dramatically reduced in the spinal cords of schistosome-infected, MOG-immunized mice. Furthermore, analysis of the cellular composition of the spinal cords and brains revealed that a preestablished infection withS. mansonidecreased central nervous system (CNS) inflammation, particularly of macrophages and CD4 T cells. These results suggest that schistosomiasis may negatively regulate the onset of EAE by downregulating the production of proinflammatory cytokines and altering CNS inflammation.
Actinobacillus actinomycetemcomitans
Serotype d-Specific Antigen Contains the O Antigen of Lipopolysaccharide
Authors: Lakio Laura , Paju Susanna , Alfthan Georg , Tiirola Terttu , Asikainen Sirkka , Pussinen Pirkko J. 
Published: August 2003

ABSTRACT

Actinobacillus actinomycetemcomitans
is a gram-negative, facultatively anaerobic bacterium which is associated especially with aggressive forms of periodontitis. Contradictory results on the localization of the
A. actinomycetemcomitans
serotype-specific antigen have been reported. The aim of the present study was to characterize the
A. actinomycetemcomitans
serotype d-specific antigen. The antigen was isolated by affinity chromatography. The affinity column was prepared from immunoglobulin G isolated from rabbit antiserum raised against
A. actinomycetemcomitans
serotype d. The isolated antigen was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and silver staining, all of which revealed a ladder-like structure typical for the O antigen of lipopolysaccharide (LPS). In a displacement enzyme-linked immunosorbent assay (ELISA), the isolated antigen displaced in a concentration-dependent manner the binding of the polyclonal rabbit antiserum raised against
A. actinomycetemcomitans
serotype d to the competing whole-cell serotype d antigen. The isolated antigen contained LPS, and an equal concentration of LPS isolated from
A. actinomycetemcomitans
serotype d gave a similar displacement curve in the ELISA. In order to test the immunogenic properties of the isolated antigen, it was used to immunize a rabbit. The antiserum raised against the isolated antigen displayed specificity in Western blotting and ELISA similar to that of antibody raised against LPS isolated from
A. actinomycetemcomitans
serotype d. In conclusion, our results show that the
A. actinomycetemcomitans
serotype d-specific antigen contains the O-antigenic structure of LPS.
Regulation of Expression of the Paralogous Mlp Family in
Borrelia burgdorferi
Authors: Yang Xiaofeng F. , Hübner Anette , Popova Taissia G. , Hagman Kayla E. , Norgard Michael V. 
Published: August 2003

ABSTRACT

The Mlp (multicopy lipoproteins) family is one of many paralogous protein families in
Borrelia burgdorferi
. To examine the extent to which the 10 members of the Mlp family in
B. burgdorferi
strain 297 might be differentially regulated, antibodies specific for each of the Mlps were developed and used to analyze the protein expression profiles of individual Mlps when
B. burgdorferi
replicated under various cultivation conditions. All of the Mlps were upregulated coordinately when
B. burgdorferi
was cultivated at either elevated temperature, reduced culture pH, or increased spirochete cell density. Inasmuch as the expression of OspC is influenced by a novel RpoN-RpoS regulatory pathway, similar induction patterns for OspC and the Mlp paralogs prompted an assessment of whether the RpoN-RpoS pathway also was involved in Mlp expression. In contrast to wild-type
B. burgdorferi
, both RpoN- and RpoS-deficient mutants were unable to upregulate OspC or the Mlp paralogs when grown at lower pH (6.8), indicating that pH-mediated regulation of OspC and Mlp paralogs is dependent on the RpoN-RpoS pathway. However, when RpoN- or RpoS-deficient mutants were shifted from 23°C to 37°C or were cultivated to higher spirochete densities, some induction of the Mlps still occurred, whereas OspC expression was abolished. The combined findings suggest that the Mlp paralogs are coordinately regulated as a family and have an expression profile similar, but not identical, to that of OspC. Although Mlp expression as a family is influenced by the RpoN-RpoS regulatory pathway, there exists at least one additional layer of gene regulation, yet to be elucidated, contributing to Mlp expression in
B. burgdorferi
.
An
Enterococcus faecium
Secreted Antigen, SagA, Exhibits Broad-Spectrum Binding to Extracellular Matrix Proteins and Appears Essential for
E. faecium
Growth
Authors: Teng Fang , Kawalec Magdalena , Weinstock George M. , Hryniewicz Waleria , Murray Barbara E. 
Published: August 2003

ABSTRACT

A gene encoding a major secreted antigen, SagA, was identified in
Enterococcus faecium
by screening an
E. faecium
genomic expression library with sera from patients with
E. faecium
-associated endocarditis. Recombinant SagA protein showed broad-spectrum binding to extracellular matrix (ECM) proteins, including fibrinogen, collagen type I, collagen type IV, fibronectin, and laminin. A fibrinogen-binding protein, purified from culture supernatants of an
E. faecium
clinical isolate, was found to match the N-terminal sequence of the predicted SagA protein and to react with the anti-SagA antibody, confirming that it was the SagA protein; this protein appeared as an 80- to 90-kDa smear on a Western blot that was sensitive to proteinase K and resistant to periodate treatment and glycoprotein staining. When overexpressed in
E. faecium
and
Escherichia coli
, the native and recombinant SagA proteins formed stable oligomers, apparently via their C-terminal domains. The SagA protein is composed of three domains: (i) a putative coiled-coil N-terminal domain that shows homology to the N-terminal domain of
Streptococcus mutans
SagA protein (42% similarity), previously shown to be involved in cell wall integrity and cell shape maintenance, and to the P45 protein of
Listeria monocytogenes
(41% similarity); (ii) a central domain containing direct repeats; and (iii) a C-terminal domain that is similar to that found in various proteins, including P45 (50% similarity) and P60 (52% similarity) of
L. monocytogenes
. The P45 and P60 proteins both have cell wall hydrolase activity, and the latter has also been shown to be involved in virulence, whereas cell wall hydrolase activity was not detected for SagA protein. The
E. faecium sagA
gene, like the
S. mutans
homologue, is located in a cluster of genes encoding proteins that appear to be involved in cell wall metabolism and could not be disrupted unless it was first transcomplemented, suggesting that the
sagA
gene is essential for
E. faecium
growth and may be involved in cell wall metabolism. In conclusion, the extracelluar
E. faecium
SagA protein is apparently essential for growth, shows broad-spectrum binding to ECM proteins, forms oligomers, and is antigenic during infection.
Analysis of RogB-Controlled Virulence Mechanisms and Gene Expression in
Streptococcus agalactiae
Authors: Gutekunst Heike , Eikmanns Bernhard J. , Reinscheid Dieter J. 
Published: August 2003

ABSTRACT

Streptococcus agalactiae
is the leading cause of bacterial sepsis and meningitis in neonates and also the causative agent of different serious infections in immunocompromised adults. The wide range of diseases that are caused by
S. agalactiae
suggests regulatory mechanisms that control the formation of specific virulence factors in these bacteria. The present study describes a gene from
S. agalactiae
, designated
rogB
, encoding a protein with significant similarity to members of the RofA-like protein (RALP) family of transcriptional regulators. Disruption of the
rogB
gene in the genome of
S. agalactiae
resulted in mutant strain RGB1, which was impaired in its ability to bind to fibrinogen and fibronectin. Mutant RGB1 also exhibited a reduced adherence to human epithelial cells but did not show an altered invasion of eukaryotic cells. By real-time PCR analysis, mutant RGB1 revealed an increased expression of the
cpsA
gene, encoding a regulator of capsule gene expression. However, strain RGB1 exhibited a reduced expression of the
rogB
gene and of two adjacent genes, encoding putative virulence factors in
S. agalactiae
. Furthermore, mutant RGB1 was impaired in the expression of the
fbsA
gene, coding for a fibrinogen receptor from
S. agalactiae
. The altered gene expression in mutant RGB1 could be restored by plasmid-mediated expression of
rogB
, confirming a RogB deficiency as the cause for the observed changes in virulence gene expression in
S. agalactiae
. Reporter gene studies with a promotorless luciferase gene fused to
fbsA
allowed a growth-dependent analysis of
fbsA
expression in
S. agalactiae
. These reporter gene studies also suggest that RogB exerts a positive effect on
fbsA
expression in
S. agalactiae
.
Cloning and Characterization of a Gene Encoding an Immunoglobulin-Binding Receptor on the Cell Surface of Some Members of the FamilyTrypanosomatidae
Authors: Campos-Neto Antonio , Suffia Isabelle , Cavassani Karen A. , Jen Shyian , Greeson Kay , Ovendale Pamela , Silva João S. , Reed Steven G. , Skeiky Yasir A. W. 
Published: August 2003

ABSTRACTSeveral members of theTrypanosomatidaefamily, when freshly isolated from their mammalian hosts, have immunoglobulins adsorbed to their cell surfaces. However, a significant portion of these antibody molecules is not parasite specific, i.e., the immunoglobulins are bound to the parasite's cell surface molecules via noncognitive interactions. It has been proposed that this noncognitive adsorption of immunoglobulins to the parasite is mediated by an Fc-like receptor present in several members of theTrypanosomatidaefamily. However, the molecular identification of this receptor has never been defined. Here, we describe the cloning of a gene encoding a protein that might represent this molecule. The gene, namedLmsp1, was cloned by screening aLeishmania majorcDNA expression library using a rabbit antiserum.Lmsp1is present in bothLeishmaniaandTrypanosomaand is expressed in all developmental stages of these parasites. The predicted protein has a molecular mass of 16.6 kDa and contains an RGD sequence starting at residue 104 and three cysteine residues at positions 55, 74, and 116. The purified recombinant protein strongly binds to normal immunoglobulins of various animal species (humans, rabbits, sheep, goats, guinea pigs, donkeys, rats, and mice) and the binding to human immunoglobulins appears to be immunoglobulin G (IgG) and IgM isotype specific. Moreover,Lmsp1binds to both purified Fc and Fab fragments of IgG from both humans and rabbits. The mapping of theLmsp1epitopes that bind human IgG revealed that different sequences of the molecule bind to Fc or Fab. In addition, fluorescence-activated cell sorter analyses with a specific rabbit anti-Lmsp1antiserum showed thatLmsp1is associated with the parasite's cell surface. Finally, inhibition experiments point to an active role of this molecule in the immunoglobulin-mediated attachment and penetration ofTrypanosoma cruziin its macrophage host cells, thus suggesting thatLmsp1is a putativeTrypanosomatidaeimmunoglobulin receptor.