bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flagellar Phase Variation ofSalmonella entericaSerovar Typhimurium Contributes to Virulence in the Murine Typhoid Infection Model but Does Not InfluenceSalmonella-Induced Enteropathogenesis
Authors: Ikeda Jack S. , Schmitt Clare K. , Darnell Stephen C. , Watson Patricia R. , Bispham Jennifer , Wallis Timothy S. , Weinstein Debra L. , Metcalf Eleanor S. , Adams Phillip , O'Connor C. David , O'Brien Alison D. 
Published: July 2002

ABSTRACTAlthoughSalmonella entericaserovar Typhimurium can undergo phase variation to alternately express two different types of flagellin subunit proteins, FljB or FliC, no biological function for this phenomenon has been described. In this investigation, we constructed phase-locked derivatives ofS. entericaserovar Typhimurium that expressed only FljB (termed locked-ON) or FliC (termed locked-OFF). The role of phase variation in models of enteric and systemic pathogenesis was then evaluated. There were no differences between the wild-type parent strain and the two phase-locked derivatives in adherence and invasion of mouse epithelial cells in vitro, survival in mouse peritoneal macrophages, or in a bovine model of gastroenteritis. By contrast, the locked-OFF mutant was virulent in mice following oral or intravenous (i.v.) inoculation but the locked-ON mutant was attenuated. When these phase-locked mutants were compared in studies of i.v. kinetics in mice, similar numbers of the two strains were isolated from the blood and spleens of infected animals at 6 and 24 h. However, the locked-OFF mutant was recovered from the blood and spleens in significantly greater numbers than the locked-ON strain by day 2 of infection. By 5 days postinfection, a majority of the mice infected with the locked-OFF mutant had died compared with none of the mice infected with the locked-ON mutant. These results suggest that phase variation is not involved in the intestinal stage of infection but that onceS. entericaserovar Typhimurium reaches the spleens of susceptible mice those organisms in the FliC phase can grow and/or survive better than those in the FljB phase. Additional experiments with wild-typeS. entericaserovar Typhimurium, fully capable of switching flagellin type, supported this hypothesis. We conclude that organisms that have switched to the FliC+phase have a selective advantage in the mouse model of typhoid fever but have no such advantage in invasion of epithelial cells or the induction of enteropathogenesis.
Effects of Superantigen and Lipopolysaccharide on Induction of CD80 through Apoptosis of Human Monocytes
Authors: Takahashi Masahiro , Takahashi Maiko , Shinohara Fumiaki , Takada Haruhiko , Rikiishi Hidemi 
Published: July 2002

ABSTRACTTo investigate the mechanisms underlying superantigen (SAg) stimulation, we analyzed the effect of SAg on monocyte responses with or without lipopolysaccharide (LPS). Addition of gamma interferon (IFN-γ) to unstimulated cultures induced a marked increase in the number of CD80+monocytes, which was inhibited by LPS through the action of interleukin-10. However, CD80+monocytes began to increase before IFN-γ production, observed after 9 h of stimulation with staphylococcal enterotoxin B (SEB). SEB selectively increased the number of apoptotic CD80−monocytes, whereas LPS-treated monocytes were resistant to the apoptotic action of SEB. This SEB-induced killing was abrogated by anti-CD95 monoclonal antibody (MAb) ZB4 and anti-CD95 ligand (CD95L) MAb NOK2, suggesting a CD95-based pathway of apoptosis. Furthermore, the numbers of SEB-induced CD80+monocytes were partially decreased by anti-CD119 (IFN-γ receptor) MAb and by anti-CD95L (NOK2) MAb. The CD30 expression of CD27highT cells induced by SEB was increased by agonistic anti-CD95 (CH11) MAb. Together, our findings showed that SEB-induced monocyte apoptosis is closely associated with the enrichment of CD80+monocytes generated before IFN-γ production, followed by up-regulation of CD80 by IFN-γ, and that LPS has negative effects in both cases. These results also suggested that induction of monocyte apoptosis is an important mechanism by which SAg exerts its anti-inflammatory effects.
Comparison of Pathogenesis and Host Immune Responses toCandida glabrataandCandida albicansin Systemically Infected Immunocompetent Mice
Authors: Brieland Joan , Essig David , Jackson Craig , Frank Doyle , Loebenberg David , Menzel Fred , Arnold Brian , DiDomenico Beth , Hare Roberta 
Published: July 2002

ABSTRACTCytokine-mediated host defense againstCandida glabratainfection was compared to that againstC. albicans, using immunocompetent murine models of systemic candidiasis. The pathogenesis of infection was evaluated morphologically and by culture of target organs, while the kinetics of induction of cytokine mRNAs and corresponding proteins were determined in kidneys by real-time reverse transcription-PCR and cytokine-specific murine enzyme-linked immunosorbent assays, respectively. Systemic infection withC. glabrataresulted in a chronic, nonfatal infection with recovery of organisms from kidneys, while intravenous inoculation withC. albicansresulted in rapid mortality with logarithmic growth of organisms in kidneys and recovery ofC. albicansfrom the spleen, liver, and lungs. Survival ofC. glabrata-infected mice was associated with rapid induction of mRNAs and corresponding immunoreactive proteins for the proinflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-12 (IL-12), and gamma interferon (IFN-γ) and the lack of induction of protein for the anti-inflammatory cytokine IL-10. In contrast, mortality inC. albicans-infected mice was associated with induction of mRNA and corresponding protein for IL-10 but delayed (i.e., TNF-α) or absent (i.e., IL-12 and IFN-γ) induction of immunoreactive proinflammatory cytokines. Mice were subsequently treated with cytokine-specific neutralizing monoclonal antibodies (MAbs) to TNF-α, IL-12, or IFN-γ, and the effect on growth ofC. glabratain kidneys was assessed. Neutralization of endogenous TNF-α resulted in a significant increase inC. glabrataorganisms compared to similarly infected mice administered an isotype-matched control MAb, while neutralization of endogenous IL-12 or IFN-γ had no significant effect onC. glabratareplication. These results demonstrate that in response to intravenous inoculation ofC. glabrata, immunocompetent mice develop chronic nonfatal renal infections which are associated with rapid induction of the proinflammatory cytokines TNF-α, IL-12, and IFN-γ. Furthermore, TNF-α plays a key role in host defense against systemic candidiasis caused by eitherC. glabrataorC. albicans, as the absence of endogenous TNF-α activity was associated with enhanced tissue burden in both infection models.
Cellular Mechanisms That Cause Suppressed Gamma Interferon Secretion in Endotoxin-Tolerant Mice
Authors: Varma Tushar K. , Toliver-Kinsky Tracy E. , Lin Cheng Y. , Koutrouvelis Aristides P. , Nichols Joan E. , Sherwood Edward R. 
Published: July 2002

ABSTRACTEndotoxin (lipopolysaccharide [LPS]) tolerance is a state of altered immunity characterized, in part, by suppression of LPS-induced gamma interferon (IFN-γ) expression. However, the cellular mediators regulating LPS-induced production of IFN-γ in normal mice and the effect of LPS tolerance on these mediators has not been well characterized. Our studies show that macrophage dysfunction is the primary factor causing suppressed IFN-γ expression in LPS-tolerant mice. Specifically, LPS-tolerant macrophages have a markedly impaired ability to induce IFN-γ secretion by T cells and NK cells obtained from either control or LPS-tolerant mice. However, T cells and NK cells isolated from LPS-tolerant mice produce normal levels of IFN-γ when cocultured with control macrophages or exogenous IFN-γ-inducing factors. Assessment of important IFN-γ-regulating factors showed that interleukin-12 (IL-12) and costimulatory signals provided by IL-15, IL-18, and CD86 are largely responsible for LPS-induced IFN-γ expression in control mice. IL-10 is an inhibitor of IFN-γ production in both the control and LPS-tolerant groups. Expression of IL-12 and the IL-12 receptor β1 (IL-12Rβ1) and IL-12Rβ2 subunits are suppressed in the spleens of LPS-tolerant mice. LPS-tolerant splenocytes also exhibit decreased production of IL-15 and IL-15Rα. However, expression of IL-18 and the B7 proteins CD80 and CD86 are unchanged or increased compared to controls after induction of LPS tolerance. CD28, a major receptor for B7 proteins, is also increased in the spleens of LPS-tolerant mice. Expression of the inhibitory cytokine IL-10 and the IL-10R are sustained after induction of LPS tolerance. These data show that suppression of IFN-γ production in LPS-tolerant mice is largely due to macrophage dysfunction and provide insight into the cellular alterations that occur in LPS tolerance. This study also better defines the factors that mediate LPS-induced IFN-γ production in normal mice.
Protective Efficacy of a DNA Vaccine Encoding Antigen 85A from
Mycobacterium bovis
BCG against Buruli Ulcer
Authors: Tanghe Audrey , Content Jean , Van Vooren Jean-Paul , Portaels Françoise , Huygen Kris 
Published: July 2002

ABSTRACT

Buruli ulcer, caused by
Mycobacterium ulcerans
, is characterized by deep and necrotizing skin lesions, mostly on the arms and legs. Together with tuberculosis and leprosy, this mycobacterial disease has become a major health problem in tropical and subtropical regions, particularly in central and western Africa. No specific vaccine is available for Buruli ulcer. There is, however, evidence in the literature that suggests a cross-reactive protective role of the tuberculosis vaccine
M. bovis
BCG. To identify potential mechanisms for this cross-protection, we identified and characterized the
M. ulcerans
homologue of the important protective mycobacterial antigen 85 (Ag85A) from BCG. The homologue is well conserved in
M. ulcerans
, showing 84.1% amino acid sequence identity and 91% conserved residues compared to the sequence from BCG. This antigen was sufficiently conserved to allow cross-reactive protection, as demonstrated by the ability of
M. ulcerans
- infected mice to exhibit strong cellular immune responses to both BCG and its purified Ag85 complex. To further address the mechanism of cross-reactive protection, we demonstrate here that prior vaccination with either BCG or plasmid DNA encoding BCG Ag85A is capable of significantly reducing the bacterial load in the footpads of
M. ulcerans
- infected mice, as determined by Ziehl-Neelsen staining and by actual counting of CFU on 7H11 Middlebrook agar. Together, the results reported here support the potential of a cross-protective Ag85-based future vaccine against tuberculosis, Buruli ulcer, and leprosy.
Genetic Immunization with the Region Encoding the α-Helical Domain of PspA Elicits Protective Immunity againstStreptococcus pneumoniae
Authors: Bosarge Joseph R. , Watt James M. , McDaniel D. Olga , Swiatlo Edwin , McDaniel Larry S. 
Published: July 2002

ABSTRACTPneumococcal surface protein A (PspA) is a pneumococcal virulence factor capable of eliciting protection against pneumococcal infection in mice. Previous studies have demonstrated that the protection is antibody mediated. Here we examined the ability ofpspAto elicit a protective immune response following genetic immunization of mice. Mice were immunized by intramuscular injections with a eukaryotic expression vector encoding the α-helical domain of PspA/Rx1. Immunization induced a PspA-specific serum antibody response, and immunized mice survived pneumococcal challenge. Survival and antibody responses occurred in a dose-dependent manner, the highest survival rates being seen with doses of 10 μg or greater. The ability of genetic immunization to elicit cross-protection was demonstrated by the survival of immunized mice challenged with pneumococcal strains differing in capsule and PspA types. Also, immunized mice were protected from intravenous and intratracheal challenges with pneumococci. Similar to the results seen with immunization with PspA, the survival of mice genetically immunized withpspAwas antibody mediated. There was no decline in the level of protection 7 months after immunization. These results support the use of genetic immunization to elicit protective immune responses against extracellular pathogens.
Central Importance of Immunoglobulin A in Host Defense againstGiardiaspp
Authors: Langford T. Dianne , Housley Michael P. , Boes Marianne , Chen Jianzhu , Kagnoff Martin F. , Gillin Frances D. , Eckmann Lars 
Published: July 2002

ABSTRACTThe protozoan pathogenGiardiais an important cause of parasitic diarrheal disease worldwide. It colonizes the lumen of the small intestine, suggesting that effective host defenses must act luminally. Immunoglobulin A (IgA) antibodies are presumed to be important for controllingGiardiainfection, but direct evidence for this function is lacking. B-cell-independent effector mechanisms also exist and may be equally important for antigiardial host defense. To determine the importance of the immunoglobulin isotypes that are transported into the intestinal lumen, IgA and IgM, for antigiardial host defense, we infected gene-targeted mice lacking IgA-expressing B-cells, IgM-secreting B-cells, or all B-cells as controls withGiardia murisorGiardia lambliaGS/M-83-H7. We found that IgA-deficient mice could not eradicate eitherG. murisorG. lambliainfection, demonstrating that IgA is required for their clearance. Furthermore, although neither B-cell-deficient nor IgA-deficient mice could clearG. murisinfections, IgA-deficient mice controlled infection significantly better than B-cell-deficient mice, suggesting the existence of B-cell-dependent but IgA-independent antigiardial defenses. In contrast, mice deficient for secreted IgM antibodies clearedG. murisinfection normally, indicating that they have no unique functions in antigiardial host defense. These data, together with the finding that B-cell-deficient mice have some, albeit limited, residual capacity to controlG. murisinfection, show that IgA-dependent host defenses are central for eradicatingGiardiaspp. Moreover, B-cell-dependent but IgA-independent and B-cell-independent antigiardial host defenses exist but are less important for controlling infection.
Reduced Infectivity of aLeishmania donovaniBiopterin Transporter Genetic Mutant and Its Use as an Attenuated Strain for Vaccination
Authors: Papadopoulou Barbara , Roy Gaétan , Breton Marie , Kündig Christoph , Dumas Carole , Fillion Isabelle , Singh Ajay K. , Olivier Martin , Ouellette Marc 
Published: July 2002

ABSTRACTPterins are essential for the growth ofLeishmaniaspecies, and recent work has led to the isolation of the biopterin transporter BT1. In this study, we inactivated theLeishmania donovanibiopterin transporter BT1 by gene disruption mediated by homologous recombination. No transport of biopterin was detected in this mutant. TheL. donovani BT1null mutant showed a much lesser capacity for inducing infection in mice than wild-type parasites and could elicit protective immunity in mice susceptible to infection against aL. donovanichallenge. Splenocytes isolated from mice immunized with theBT1null mutant parasites produced significant amounts of interferon gamma following stimulation withL. donovanipromastigotes as measured by enzyme-linked immunosorbent assay and enzyme-linked immunospot assays. Overall, these results show that by genetically manipulating the pterin transport inL. donovani, it is possible to generate an attenuated organism that could be part of a vaccination strategy.
Transient Requirement of the PrrA-PrrB Two-Component System for Early Intracellular Multiplication of
Mycobacterium tuberculosis
Authors: Ewann Fanny , Jackson Mary , Pethe Kevin , Cooper Andrea , Mielcarek Nathalie , Ensergueix Danielle , Gicquel Brigitte , Locht Camille , Supply Philip 
Published: July 2002

ABSTRACT

Adaptive regulation of gene expression in response to environmental changes is a general property of bacterial pathogens. By screening an ordered transposon mutagenesis library of
Mycobacterium tuberculosis
, we have identified three mutants containing a transposon in the coding sequence or in the 5′ regions of genes coding for two-component signal transduction systems (
trcS
,
regX3
,
prrA
). The intracellular multiplication capacity of the three mutants was investigated in mouse bone marrow-derived macrophages. Only the
prrA
mutant showed a defect in intracellular growth during the early phase of infection, and this defect was fully reverted when the mutant was complemented with
prrA-prrB
wild-type copies. The mutant phenotype was transient, as after 1 week this strain recovered full growth capacity to reach levels similar to that of the wild type at day 9. Moreover, a transient induction of
prrA
promoter activity was observed during the initial phase of macrophage infection, as shown by a
prrA
promoter
-gfp
fusion in
M. bovis
BCG infecting the mouse macrophages. The concordant transience of the
prrA
mutant phenotype and
prrA
promoter activity indicates that the PrrA-PrrB two-component system is involved in the environmental adaptation of
M. tuberculosis
, specifically in an early phase of the intracellular growth, and that, similar to other facultative intracellular parasites,
M. tuberculosis
can use genes temporarily required at different stages in the course of macrophage infection.
Biofilm Formation and Interaction with the Surfaces of Gallstones by
Salmonella
spp
Authors: Prouty A. M. , Schwesinger W. H. , Gunn J. S. 
Published: July 2002

ABSTRACT

Salmonellae can exist in an asymptomatic carrier state in the human gallbladder. Individuals with gallstones are more likely to become typhoid carriers, and antibiotic treatments are often ineffectual against
Salmonella enterica
serovar Typhi in carriers with gallstones. Therefore, we hypothesized that
Salmonella
spp. form biofilms on the surfaces of gallstones, where the bacteria are protected from high concentrations of bile and antibiotics. A number of methods were utilized to examine biofilm formation on human gallstones and glass coverslips in vitro, including confocal, light, and scanning electron microscopy. In our assays, salmonellae formed full biofilms on the surfaces of gallstones within 14 days and appeared to excrete an exopolysaccharide layer that bound them to the surfaces and to other bacteria. Efficient biofilm formation on gallstones was dependent upon the presence of bile, as a biofilm did not form on gallstones within 14 days in Luria-Bertani broth alone. The biofilms formed by a
Salmonella enterica
serovar Typhi Vi antigen mutant, as well as strains with mutations in genes that eliminate production of four different fimbriae, were indistinguishable from the biofilms formed by the parents. Mutants with an incomplete O-antigen, mutants that were nonmotile, and mutants deficient in quorum sensing were unable to develop complete biofilms. In addition, there appeared to be selectivity in salmonella binding to the gallstone surface that did not depend on the topology or surface architecture. These studies should aid in the understanding of the
Salmonella
carrier state, an important but underresearched area of typhoid fever pathogenesis. If the basis of carrier development can be understood, it may be possible to identify effective strategies to prevent or treat this chronic infection.
Segmented Filamentous Bacteria Interact with Intraepithelial Mononuclear Cells
Authors: Meyerholz David K. , Stabel Thomas J. , Cheville Norman F. 
Published: July 2002

ABSTRACT
Segmented filamentous bacteria (SFB) are found in multiple species and play an important role in the development of mucosal immunity. The mechanism by which the bacteria interact with the immune system has not been well defined. We provide morphologic evidence of direct interaction between SFB and intraepithelial mononuclear cells.
mRNA Composition and Control of Bacterial Gene Expression
Authors: Liang S.-T. , Xu Y.-C. , Dennis P. , Bremer H. 
Published: July 2002

ABSTRACT

The expression of any given bacterial protein is predicted to depend on (i) the transcriptional regulation of the promoter and the translational regulation of its mRNA and (ii) the synthesis and translation of total (bulk) mRNA. This is because total mRNA acts as a competitor to the specific mRNA for the binding of initiation-ready free ribosomes. To characterize the effects of mRNA competition on gene expression, the specific activity of β-galactosidase expressed from three different promoter-
lacZ
fusions (P
spc
-
lacZ
, P
RNAI
-
lacZ
, and P
RNAII
-
lacZ
) was measured (i) in a
relA
+
background during exponential growth at different rates and (ii) in
relA
+
and Δ
relA
derivatives of
Escherichia coli
B/r after induction of a mild stringent or a relaxed response to raise or lower, respectively, the level of ppGpp. Expression from all three promoters was stimulated during slow exponential growth or at elevated levels of ppGpp and was reduced during fast exponential growth or at lower levels of ppGpp. From these observations and from other considerations, we propose (i) that the concentration of free, initiation-ready ribosomes is approximately constant and independent of the growth rate and (ii) that bulk mRNA made during slow growth and at elevated levels of ppGpp is less efficiently translated than bulk mRNA made during fast growth and at reduced levels of ppGpp. These features lead to an indirect enhancement in the expression of LacZ (or of any other protein) during growth in media of poor nutritional quality and at increased levels of ppGpp.
The Alternative Sigma Factor RpoN Is Required for
hrp
Activity in
Pseudomonas syringae
pv. Maculicola and Acts at the Level of
hrpL
Transcription
Authors: Hendrickson Erik L. , Guevera Pablo , Ausubel Frederick M. 
Published: July 2002

ABSTRACT

β-Glucuronidase (
uidA
) reporter gene fusions were constructed for the
hrpZ
,
hrpL
, and
hrpS
genes from the phytopathogen
Pseudomonas syringae
pv. maculicola strain ES4326. These reporters, as well as an
avrRpt2-uidA
fusion, were used to measure transcriptional activity in ES4326 and a ES4326
rpoN
mutant.
rpoN
was required for the expression of
avrRpt2
,
hrpZ
, and
hrpL
in vitro in minimal media and in vivo when infiltrated into
Arabidopsis thaliana
leaves. In contrast, the expression of
hrpS
was essentially the same in wild-type and
rpoN
mutant strains. Constitutive expression of
hrpL
in an
rpoN
mutant restored
hrpZ
transcription to wild-type levels, restored the hypersensitive response when infiltrated into tobacco (
Nicotiana tobacum
), and partially restored the elicitation of virulence-related symptoms but not growth when infiltrated into
Arabidopsis
leaves. These data indicate that
rpoN
-mediated control of
hrp
gene expression acts at the level of
hrpL
and that in planta growth of
P. syringae
is not required for the elicitation of disease symptoms.
The FtsH Protein Accumulates at the Septum of
Bacillus subtilis
during Cell Division and Sporulation
Authors: Wehrl Wolfgang , Niederweis Michael , Schumann Wolfgang 
Published: July 2002

ABSTRACT

The
ftsH
gene encodes an ATP- and Zn
2+
-dependent metalloprotease which is anchored to the cytoplasmic membrane via two transmembrane segments in such a way that the very short amino- and the long carboxy termini are exposed to the cytoplasm. Deletion of the
ftsH
gene in
Bacillus subtilis
results in a pleiotropic phenotype such as filamentous growth. This observation prompted us to ask whether
ftsH
is involved in cell division. A translational fusion was constructed between the complete coding region of
ftsH
and
gfp
+
the latter carrying five point mutations to obtain enhanced fluorescence. We detected that the FtsH protein accumulates in the midcell septum of dividing cells, and during sporulation first in the asymmetrically located septa of sporulating cells and later in the membrane which engulfs the forespore. These observations revealed a new function of FtsH.