bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mycobacterium bovisBCG-Infected Mice Are More Susceptible to Staphylococcal Enterotoxin B-Mediated Toxic Shock than Uninfected Mice despite Reduced In Vitro Splenocyte Responses to Superantigens
Authors: Pedras-Vasconcelos João A. , Chapdelaine Yvan , Dudani Renu , van Faassen Henk , Smith Dean K. , Sad Subash 
Published: July 2002

ABSTRACTType 1 T-cell responses against intracellular pathogens play a crucial role in mediating protection. We examined whether the induction of a strong type 1 T-cell response during a chronic bacterial infection influences responses to superantigens capable of inducing acute shock. Intravenous infection of mice withMycobacterium bovisBCG appeared to induce a progressive anergy towards staphylococcal enterotoxin B (SEB) and towards antigen preparation of BCG (BCG-Ag) itself, based on diminished gamma interferon (IFN-γ) production by SEB- and BCG-Ag-stimulated splenocytes from infected mice. In contrast to these in vitro results, injection of SEB into BCG-infected mice led to a dramatic increase in the serum IFN-γ levels and the death of infected but not of control mice. In vitro hyporesponsiveness towards SEB and BCG-Ag occurred only with unfractionated splenocyte cultures, as purified T cells from infected mice produced higher levels of IFN-γ. Hyporesponsiveness towards SEB and BCG-Ag in unfractionated splenocyte cultures was not due to suppressive antigen-presenting cells (APCs), as APCs from infected mice stimulated higher levels of IFN-γ from purified T cells. The diminished IFN-γ levels observed with bulk splenocytes appear to be due to changes in the T-cell-to-APC ratio that result in a decreased proportion of T cells, coupled to reduced proliferative responses and an increased susceptibility of effector T cells to activation-induced cell death in vitro. Our results indicate that the reported phenomena of T-cell anergy during mycobacterial infection may be an in vitro consequence of the development of a strong type 1 response in vivo.
Evidence That the Variable Regions of the Central Domain of VlsE Are Antigenic during Infection with Lyme Disease Spirochetes
Authors: McDowell John V. , Sung Shian-Ying , Hu Linden T. , Marconi Richard T. 
Published: July 2002

ABSTRACTIt has been postulated that thevlssystem of the Lyme disease spirochetes contributes to immune evasion through antigenic variation. While it is clear thatvlsEundergoes sequence change within its variable regions at a high frequency during the early stages of infection, a definitive role in immune evasion has not been demonstrated. In this report we assessed the murine and human humoral immune response to recombinant (r)-VlsE variants that originally arose during infection in mice. Immunoblot analyses of r-VlsE variants were conducted by using serum samples collected from mice infected withBorrelia burgdorfericlones that carried differentvlsEvariants. All of the r-VlsE variants were recognized by infection sera regardless of the identity of the infecting clone or isolate. In addition, all variants were immunoreactive with a panel of human Lyme disease patient serum samples. It is evident from these analyses that the infection-induced VlsE variants share common epitopes that reside within conserved segments of these proteins. However, preabsorption experiments revealed that the variable regions of the central domain of VlsE, which undergo rapid mutation during infection, also influence the antigenic properties of the protein. A subset of the antibodies elicited againstvlsEvariants that differ in the sequences of their variable regions were found to be variant specific. Hence, in spite of a robust antibody response to conserved segments of VlsE, infection-induced sequence changes within the variable regions alter the antigenicity of VlsE. These results provide the first direct evidence of antigenic variation in the VlsE protein.
Streptococcus suisInteractions with the Murine Macrophage Cell Line J774: Adhesion and Cytotoxicity
Authors: Segura Mariela , Gottschalk Marcelo 
Published: July 2002

ABSTRACTStreptococcus suiscapsular type 2 is an important etiological agent of swine meningitis, and it is also a zoonotic agent. Since one hypothesis of the pathogenesis ofS. suisinfection is that bacteria enter the bloodstream and invade the meninges and other tissues in close association with mononuclear phagocytes, the objective of the present study was to evaluate the capacity ofS. suistype 2 to adhere to macrophages. An enzyme-linked immunosorbent assay technique was standardized to simply and accurately measure the rate of bacterial attachment to phagocytic cells. Results were confirmed by plate counting. Adhesion was dependent on bacterial concentration and incubation time and was not affected by cytochalasin pretreatment of macrophages. Inhibition studies showed that the sialic acid moiety of theS. suiscapsule would be, at least in part, responsible for bacterial recognition by macrophages. Serum preopsonization of bacteria increased adhesion levels. Complement would be partially implicated in the serum-enhanced binding ofS. suisto cells. Adhesion varied among differentS. suistype 2 isolates. However, high bacterial concentrations of several isolates were cytotoxic for cells, and these cytotoxic effects correlated with suilysin production. Indeed, hemolytic strain supernatants, as well as purified suilysin, reproduced cytotoxic effects observed with live bacteria, and these effects were inhibited by cholesterol pretreatment. Bacterial adhesion and cytotoxicity were confirmed by scanning and transmission electron microscopy. We hypothesize that attachment of bacteria to phagocytes could play an important role in the pathogenesis ofS. suisinfection by allowing bacterial dissemination and causing a bacteremia and/or septicemia. This interaction could also be related to the activation of the host inflammatory response observed during meningitis.
Contribution of Phospholipomannan to the Surface Expression of β-1,2-Oligomannosides inCandida albicansand Its Presence in Cell Wall Extracts
Authors: Poulain D. , Slomianny C. , Jouault T. , Gomez J. M. , Trinel P. A. 
Published: July 2002

ABSTRACTβ-1,2-Oligomannosides (β-1,2-Man) derived fromCandida albicansmannan have been shown to act as adhesins and to induce protective antibodies. We used monoclonal antibodies specific for β-1,2-Man in electron, confocal, and fluorescence microscopy to study the surface expression of β-1,2-Man epitopes. These monoclonal antibodies were also used for Western blotting of cell surface extracts to study the nature of the molecules expressing the β-Man epitopes. Evidence was obtained for the contribution of a glycolipid, phospholipomannan (PLM), to the complex expression of β-1,2-Man epitopes at the cell wall surfaces of yeasts grown on solid media. PLM was present in intercellular matrixes of colonies grown on agar and was detected as a contaminant in mannan batches prepared by conventional methods.
Protection of Rhesus Macaques against LethalPlasmodium knowlesiMalaria by a Heterologous DNA Priming and Poxvirus Boosting Immunization Regimen
Authors: Rogers William O. , Weiss Walter R. , Kumar Anita , Aguiar João C. , Tine John A. , Gwadz Robert , Harre Joseph G. , Gowda Kalpana , Rathore Dharmendar , Kumar Sanjai , Hoffman Stephen L. 
Published: July 2002

ABSTRACTWe tested a cytokine-enhanced, multiantigen, DNA priming and poxvirus boosting vaccine regimen for prevention of malaria in thePlasmodium knowlesi-rhesus macaque model system. Animals were primed with a mixture of DNA plasmids encoding two preerythrocytic-stage proteins and two erythrocytic-stage proteins fromP. knowlesiand combinations of the cytokines granulocyte-macrophage colony-stimulating factor, interleukin-4, and tumor necrosis factor alpha and were boosted with a mixture of four recombinant, attenuated vaccinia virus strains encoding the fourP. knowlesiantigens. Two weeks after boosting, the geometric mean immunofluorescence titers in the immunized groups against sporozoites and infected erythrocytes ranged from 160 to 8,096 and from 1,810 to 5,120, respectively. The geometric mean anti-P. knowlesicircumsporozoite protein (PkCSP) titers ranged from 1,761 to 24,242. Peripheral blood mononuclear cells (PBMC) from the immunized monkeys produced gamma interferon (IFN-γ) in response to incubation with pooled peptides from the PkCSP at frequencies of 10 to 571 spot-forming cells/106PBMC. Following challenge with 100 infectiousP. knowlesisporozoites, 2 of 11 immunized monkeys were sterilely protected, and 7 of the 9 infected monkeys resolved their parasitemias spontaneously. In contrast, all four controls became infected and required treatment for overwhelming parasitemia. Early protection was strongly associated with IFN-γ responses against a pool of peptides from the preerythrocytic-stage antigen, PkCSP. These findings demonstrate that a multistage, multiantigen, DNA priming and poxvirus boosting vaccine regimen can protect nonhuman primates from an otherwise lethal malaria sporozoite challenge.
Differential Expression of Virulence-Related Genes in
Enterococcus faecalis
in Response to Biological Cues in Serum and Urine
Authors: Shepard Brett D. , Gilmore Michael S. 
Published: July 2002

ABSTRACT

Enterococci rank among leading causes of nosocomial bacteremia and urinary tract infection and are also a leading cause of community acquired subacute endocarditis. Limited evidence suggests that biological cues in serum and urine may play an important role in modulating enterococcal virulence at sites of infection. To determine the extent to which biological cues affect enterococcal virulence-associated gene expression, we used quantitative real-time PCR to compare mRNA levels in
Enterococcus faecalis
cultures grown in serum or urine to that achieved in laboratory medium. Both environment- and growth phase-specific variations were observed, demonstrating the occurrence of as-yet-uncharacterized mechanisms for control of gene expression in
E. faecalis
that may play an important role in vivo.
AhagMutant ofMoraxella catarrhalisStrain O35E Is Deficient in Hemagglutination, Autoagglutination, and Immunoglobulin D-Binding Activities
Authors: Pearson Melanie M. , Lafontaine Eric R. , Wagner Nikki J. , St. Geme Joseph W. , Hansen Eric J. 
Published: July 2002

ABSTRACTPrevious studies correlated the presence of a 200-kDa protein on the surface ofMoraxella catarrhaliswith the ability of this organism to agglutinate human erythrocytes (M. Fitzgerald, R. Mulcahy, S. Murphy, C. Keane, D. Coakley, and T. Scott, FEMS Immunol. Med. Microbiol. 18:209-216, 1997). In the present study, the gene encoding the 200-kDa protein (designated Hag) ofM. catarrhalisstrain O35E was subjected to nucleotide sequence analysis and then was inactivated by insertional mutagenesis. The isogenichagmutant was unable to agglutinate human erythrocytes and lost its ability to autoagglutinate but was still attached at wild-type levels to several human epithelial cell lines. Thehagmutation also eliminated the ability of this mutant strain to bind human immunoglobulin D. The presence of the Hag protein on theM. catarrhaliscell surface, as well as that of the UspA1 and UspA2 proteins (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367-4377, 1997), was investigated by transmission electron and cryoimmunoelectron microscopy. Wild-typeM. catarrhalisstrain O35E possessed a dense layer of surface projections, whereas an isogenicuspA1 uspA2 hagtriple mutant version of this strain did not possess any detectable surface projections. Examination of auspA1 uspA2double mutant that expressed the Hag protein revealed the presence of a relatively sparse layer of surface projections, similar to those seen on auspA2 hagmutant that expressed UspA1. In contrast, auspA1 hagmutant that expressed UspA2 formed a very dense layer of relatively short surface projections. These results indicate that the surface-exposed Hag protein and UspA1 and UspA2 have the potential to interact both with each other and directly with host defense systems.
Opsonization Modulates Rac-1 Activation during Cell Entry byLeishmania amazonensis
Authors: Morehead J. , Coppens I. , Andrews N. W. 
Published: July 2002

ABSTRACTLesions caused byLeishmania amazonensisnormally heal, but relapses occur due to parasite persistence in host tissues. It has been proposed that infection of fibroblasts plays an important role in this process by providing the parasites with a safe haven in which to replicate. However, most previous studies have focused on the entry ofLeishmaniainto macrophages, a process mediated by serum opsonins. To gain insight into a possible role of nonopsonic entry in the intracellular persistence of amastigotes, we examined the invasion of Chinese hamster ovary (CHO) cells. Amastigotes entered CHO cells by a cytochalasin D, genistein, wortmannin, and 2,3-butanedione monoxime-sensitive pathway and replicated within phagolysosomes. However, unlike most phagocytic processes described to date, amastigote internalization in CHO cells involved activation of the GTPases Rho and Cdc42 but not Rac-1. When uptake was mediated by fibronectin or when amastigotes were opsonized with immunoglobulin G and internalized by Fc receptor-expressing CHO cells, Rac-1 activation was restored and found to be required for parasite internalization. Given the essential role of Rac in assembly of the respiratory burst oxidase, invasion through this nonopsonic, Rac-1-independent pathway may play a central role in the intracellular survival ofLeishmaniain immune hosts.
The
Enterococcus faecalis fsrB
Gene, a Key Component of the
fsr
Quorum-Sensing System, Is Associated with Virulence in the Rabbit Endophthalmitis Model
Authors: Mylonakis Eleftherios , Engelbert Michael , Qin Xiang , Sifri Costi D. , Murray Barbara E. , Ausubel Frederick M. , Gilmore Michael S. , Calderwood Stephen B. 
Published: July 2002

ABSTRACT

We used a rabbit endophthalmitis model to explore the role of
fsrB
, a gene required for the function of the
fsr
quorum-sensing system of
Enterococcus faecalis
, in pathogenicity. A nonpolar deletion mutant of
fsrB
had significantly reduced virulence compared to wild type. Complementation of mutation restored virulence. These data corroborate the role of
fsrB
in
E. faecalis
pathogenesis and suggest that the rabbit endophthalmitis model can be used to study the in vivo role of quorum sensing.
Network of Hydrogenase Maturation in
Escherichia coli
: Role of Accessory Proteins HypA and HybF
Authors: Hube Michaela , Blokesch Melanie , Böck August 
Published: July 2002

ABSTRACT

We have studied the roles of the auxiliary protein HypA and of its homolog HybF in hydrogenase maturation. A mutation in
hypA
leads to the nearly complete blockade of maturation solely of hydrogenase 3 whereas a lesion in
hybF
drastically but not totally reduces maturation and activity of isoenzymes 1 and 2. The residual level of matured enzymes in the
hybF
mutant was shown to be due to the function of HypA; HybF, conversely, was responsible for a minimal residual activity of hydrogenase 3 in the mutant
hypA
strain. Accordingly, a
hypA
Δ
hybF
double mutant was completely blocked in the maturation process. However, the inclusion of high nickel concentrations in the medium could restore limited activity of all three hydrogenases. The results of this study and of previous work (M. Blokesch, A. Magalon, and A. Böck, J. Bacteriol.
189:
2817-2822, 2001) show that the maturation of the three functional hydrogenases from
Escherichia coli
is intimately connected via the activity of proteins HypA and HypC and of their homologs HybF and HybG, respectively. The results also support the suggestion of Olson et al. (J. W. Olson, N. S. Mehta, and R. J. Maier, Mol. Microbiol.
39:
176-182, 2001) that HypA cooperates with HypB in the insertion of nickel into the precursor of the large hydrogenase subunit. Whereas HypA is predominantly involved in the maturation of hydrogenase 3, HybF takes over its function in the maturation of isoenzymes 1 and 2.
Patterns of Sequence Conservation in the S-Layer Proteins and Related Sequences in
Clostridium difficile
Authors: Calabi Emanuela , Fairweather Neil 
Published: July 2002

ABSTRACT

Clostridium difficile
is the etiological agent of antibiotic-associated diarrhea. Among the factors that may play a role in infection are S-layer proteins (SLPs). Previous work has shown these to consist mainly of two components, resulting from the cleavage of a precursor encoded by the
slpA
gene. The high-molecular-weight (MW) subunit is related both to amidases from
B. subtilis
and to at least another 28 gene products in
C. difficile
strain 630. To gain insight into the functions of the SLPs and related proteins, we have further investigated the pattern of variability both at the
slpA
locus and at six nearby paralogs. Sequencing of the
slpA
gene from an S-layer group II strain and a variant S-layer group strain confirms a high degree of divergence in the low-MW SLP, which may result from diversifying selection. A highly conserved motif, however, is found at the C terminus in all low-MW subunits and may be essential for SlpA precursor cleavage. In strain 167, a variant cleavage product is present, suggesting a secondary processing site. Southern blotting analysis shows
slpA
-like open reading frames (ORFs) 2 to 7 to be conserved in all nine strains tested, with one exception: ORF2, which encodes a 66-kDa polypeptide coextracted at low pH with the main SLPs in strain 630, may be partially deleted in strain 167. Polymorphism within the
slpA
-ORF7 cluster may be more pronounced in the region proximal to the
slpA
gene. Unexpectedly, a high-MW subunit probe cross hybridizes to sequences outside the
slpA
locus, which appear to vary in number in different strains.
Microarray Analysis of the
Mycobacterium tuberculosis
Transcriptional Response to the Acidic Conditions Found in Phagosomes
Authors: Fisher Mark A. , Plikaytis Bonnie B. , Shinnick Thomas M. 
Published: July 2002

ABSTRACT

We used microarrays and real-time reverse transcription-PCR to analyze the global transcriptional response of
Mycobacterium tuberculosis
to low pH in vitro, which may mimic an environmental signal encountered by phagocytosed mycobacteria. Eighty-one genes were differentially expressed >1.5-fold, including many involved in fatty acid metabolism. The most highly induced genes showed homology with nonribosomal peptide synthetases/polyketide synthases.
The BaeSR Two-Component Regulatory System Activates Transcription of the
yegMNOB
(
mdtABCD
) Transporter Gene Cluster in
Escherichia coli
and Increases Its Resistance to Novobiocin and Deoxycholate
Authors: Baranova Natalya , Nikaido Hiroshi 
Published: July 2002

ABSTRACT

Screening of random fragments of
Escherichia coli
genomic DNA for their ability to increase the novobiocin resistance of a hypersusceptible Δ
acrAB
mutant resulted in the isolation of a plasmid containing
baeR
, which codes for the response regulator of the two-component regulatory system BaeSR. When induced for expression,
baeR
cloned in multicopy plasmid pTrc99A significantly increased the resistance of the Δ
acrAB
host strain to novobiocin (16-fold) and to deoxycholate (8-fold). Incubation of cells with novobiocin followed by a chromatographic assay for intracellular drug showed that overproduced BaeR decreased drastically the drug accumulation, presumably via increased active efflux. The genes
baeSR
are part of a putative operon,
yegMNOB baeSR
. Direct binding of BaeR to the
yegM
promoter was demonstrated in vitro by gel retardation assay. The gene
yegB
, which codes for a major facilitator superfamily transporter, was not necessary for increased resistance, but deletion of
yegO
or an in-frame deletion of
yegN
, both of which code for resistance-nodulation-cell division-type multidrug transporters, abolished the BaeR-induced increase in resistance. It is likely that both YegN and YegO produce a complex(es) with the membrane fusion protein family member YegM and pump out novobiocin and deoxycholate. We accordingly propose to rename
yegMNOB
as
mdtABCD
(
mdt
for multidrug transporter). Finally, the expression of two other genes,
yicO
and
ygcL
, was shown to be regulated by BaeR, but it is not known if they play any roles in resistance.
Cooperativity in Signal Transfer through the Uhp System ofEscherichia coli
Authors: Verhamme Daniël T. , Postma Pieter W. , Crielaard Wim , Hellingwerf Klaas J. 
Published: July 2002

ABSTRACTThe UhpABC regulatory system in enterobacteria controls the expression of the hexose phosphate transporter UhpT. Signaling is initiated through sensing of extracellular glucose 6-phosphate by membrane-bound UhpC, which in turn modulates the histidine-protein kinase UhpB. Together with the cytoplasmic response regulator UhpA, they constitute a typical two-component regulatory system based on His-to-Asp phosphoryl transfer. Activated (i.e., phosphorylated) UhpA binds to the promoter region ofuhpT, resulting in initiation of transcription. We have investigated the contribution of transmembrane signaling (through UhpBC) and intracellular activation (through UhpA) to the overall Uhp response (UhpT expression) in vivo. UhpA activation could be made independent of transmembrane signaling when ΔuhpBCcells were grown on pyruvate. Inorganic phosphate interfered with glucose 6-phosphate-dependent, UhpBC-mediated, as well as pyruvate-mediated activation of UhpA. The relationship between the concentration of inducer (glucose 6-phosphate) and the Uhp induction rate was nonhyperbolic, indicating positive cooperativity. The degree of cooperativity was affected by the carbon or energy source available to the cells for growth. As pyruvate-mediated activation of UhpA in ΔuhpBCcells could result in considerably stronger UhpT expression than glucose 6-phosphate-dependent activation through UhpBC, the observed positive cooperativity for the overall pathway in wild-type cells may reflect the previously described cooperative binding of UhpA to theuhpTpromoter (J. L. Dahl et al., J. Biol. Chem.272:1910-1919, 1997).