bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Biofilms Formed byCandidaalbicansandCandidaparapsilosison Bioprosthetic Surfaces
Authors: Kuhn D. M. , Chandra J. , Mukherjee P. K. , Ghannoum M. A. 
Published: July 2002

ABSTRACTLittle is known about fungal biofilms, which may cause infection and antibiotic resistance. In this study, biofilm formation by differentCandidaspecies, particularlyCandidaalbicansandC.parapsilosis, was evaluated by using a clinically relevant model ofCandidabiofilm on medical devices.Candidabiofilms were allowed to form on silicone elastomer and were quantified by tetrazolium (XTT) and dry weight (DW) assays. Formed biofilm was visualized by using fluorescence microscopy and confocal scanning laser microscopy with Calcofluor White (Sigma Chemical Co., St. Louis, Mo.), concanavalin A-Alexafluor 488 (Molecular Probes, Eugene, Oreg.), and FUN-1 (Molecular Probes) dyes. Although minimal variations in biofilm production among invasiveC.albicansisolates were seen, significant differences between invasive and noninvasive isolates (P< 0.001) were noted.C.albicansisolates produced more biofilm thanC.parapsilosis,C.glabrata, andC.tropicalisisolates, as determined by DW assays (Pwas <0.001 for all comparisons) and microscopy. Interestingly, noninvasive isolates demonstrated a higher level of XTT activity than invasive isolates. On microscopy,C.albicansbiofilms had a morphology different from that of other species, consisting of a basal blastospore layer with a dense overlying matrix composed of exopolysaccharides and hyphae. In contrast,C.parapsilosisbiofilms had less volume thanC.albicansbiofilms and were comprised exclusively of clumped blastospores. Unlike planktonically grown cells,Candidabiofilms rapidly (within 6 h) developed fluconazole resistance (MIC, >128 μg/ml). Importantly, XTT and FUN-1 activity showed biofilm cells to be metabolically active. In conclusion, our data show thatC.albicansproduces quantitatively larger and qualitatively more complex biofilms than other species, in particular,C.parapsilosis.
Shigella flexneriInteractions with the Basolateral Membrane Domain of Polarized Model Intestinal Epithelium: Role of Lipopolysaccharide in Cell Invasion and in Activation of the Mitogen-Activated Protein Kinase ERK
Authors: Köhler Henrik , Rodrigues Sonia P. , McCormick Beth A. 
Published: July 2002

ABSTRACTAn early step governingShigella flexneripathogenesis is the invasion of the colonic epithelium from the basolateral surface followed by disruption of the colonic epithelial barrier. Despite recent insight intoS. flexneri-host interactions, much remains to be determined regarding the nature of the initial contact betweenS. flexneriand the host epithelial basolateral membrane domain. Since the lipopolysaccharide (LPS) is located at the outermost part of the bacterial membrane, we considered that this component might be used byS. flexnerito attach to the basolateral surface of the intestinal epithelium and promote a proinflammatory response. Therefore, polarized human T84 intestinal epithelial cells were infected from the basolateral surface with either wild-typeS. flexnerior one of its isogenic LPS-defective strains with mutations in eitherrfc,rfaL, orgalU. We found that both adherence to and internalization into the basolateral surface of a polarized intestinal epithelium withS. flexneriwere highly dependent on the length of the LPS (i.e.,rfc>rfaL>galU). Furthermore, the addition of the anti-inflammatory LPS (RsDPLA) considerably decreased the invasion profile of wild-typeS. flexneriby nearly 50%. Since LPS is associated with host inflammation, we further examined whether this molecule was involved inShigella-induced inflammatory events. We found thatS. flexneriLPS plays an important role in mediating epithelial-derived signaling, which leads to directed migration of polymorphonuclear leukocytes across model intestinal epithelium. This signaling most likely involves the activation of the mitogen-activated protein kinase extracellular regulated kinase. Thus, our findings have important implications on the understanding of the mechanisms by whichS. flexnerican elicit mucosal inflammation.
Characterization of Humoral and Cellular Immune Responses Elicited by Meningococcal Carriage
Authors: Robinson K. , Neal K. R. , Howard C. , Stockton J. , Atkinson K. , Scarth E. , Moran J. , Robins A. , Todd I. , Kaczmarski E. , Gray S. , Muscat I. , Slack R. , Ala'Aldeen D. A. A. 
Published: July 2002

ABSTRACTIn order to study the immune response elicited by asymptomatic carriage ofNeisseria meningitidis, samples of serum, peripheral blood mononuclear cells (PBMCs), and saliva were collected from a cohort of more than 200 undergraduate students in Nottingham, United Kingdom, who were subject to high rates of acquisition and carriage of meningococci. Serum immunoglobulin G levels were elevated following increases in the rate of carriage, and these responses were specific for the colonizing strains. In order to investigate T-cell responses, PBMCs from 15 individuals were stimulated with a whole-cell lysate of the H44/76 meningococcal strain (B:15:P1.7,16), stained to detect cell surface markers and intracellular cytokines, and examined by flow cytometry. The cells were analyzed for expression of CD69 (to indicate activation), gamma interferon (IFN-γ) (a representative T-helper 1 subset [Th1]-associated cytokine), and interleukin-5 (IL-5) (a Th2-associated cytokine). Following a brief meningococcal stimulation, the numbers of CD69+IFN-γ+CD56/16+NK cells were much higher than cytokine-positive CD4+events. Both IFN-γ+and IL-5+events were detected among the CD69+CD4+population, leading to the conclusion that an unbiased T-helper subset response was elicited by meningococcal carriage.
HLA-B27-Transfected (SalmonellaPermissive) and HLA-A2-Transfected (SalmonellaNonpermissive) Human Monocytic U937 Cells Differ in Their Production of Cytokines
Authors: Ekman Päivi , Saarinen Marja , He Qiushui , Gripenberg-Lerche Christel , Grönberg Alvar , Arvilommi Heikki , Granfors Kaisa 
Published: July 2002

ABSTRACTThe cytokine secretion of theSalmonella-permissive, HLA-B27-positive U937 cells was examined, as it was previously shown that these cells killSalmonellaless efficiently than controls.Salmonella-permissive U937 cells showed upregulated production of interleukin 10 and to a lesser extent tumor necrosis factor alpha. HLA-B27-associated modulation of cytokine responses may have importance in the pathogenesis of reactive arthritis.
Lipoteichoic Acids fromLactobacillus johnsoniiStrain La1 andLactobacillus acidophilusStrain La10 Antagonize the Responsiveness of Human Intestinal Epithelial HT29 Cells to Lipopolysaccharide and Gram-Negative Bacteria
Authors: Vidal Karine , Donnet-Hughes Anne , Granato Dominique 
Published: July 2002

ABSTRACTIntestinal epithelial cells (IECs) respond to lipopolysaccharide (LPS) from gram-negative bacteria in the presence of the soluble form of CD14 (sCD14), a major endotoxin receptor. Since sCD14 is also known to interact with gram-positive bacteria and their components, we looked at whether sCD14 could mediate their effects on human IECs. To this end, we examined the production of proinflammatory cytokines following exposure of the IECs to specific gram-positive bacteria or their lipoteichoic acids (LTAs) in the absence and presence of human milk as a source of sCD14. In contrast to LPS fromEscherichia coliorSalmonella enteritidis, neither the gram-positive bacteriaLactobacillus johnsoniistrain La1 andLactobacillus acidophilusstrain La10 nor their LTAs stimulated IECs, even in the presence of sCD14. However, both LTAs inhibited the sCD14-mediated LPS responsiveness of IECs. We have previously hypothesized that sCD14 in human milk is a means by which the neonate gauges the bacterial load in the intestinal lumen and liberates protective proinflammatory cytokines from IECs. The present observations suggest that gram-positive organisms, via their LTAs, temper this response and prevent an exaggerated inflammatory response.
Evaluation of Receptor Binding Specificity ofEscherichia coliK88 (F4) Fimbrial Adhesin Variants Using Porcine Serum Transferrin and Glycosphingolipids as Model Receptors
Authors: Grange Philippe A. , Mouricout Michèle A. , Levery Steven B. , Francis David H. , Erickson Alan K. 
Published: July 2002

ABSTRACTDiarrheal disease caused by enterotoxigenicEscherichia coliexpressing the K88 (F4) fimbrial adhesin (K88 ETEC) is a significant source of mortality and morbidity among newborn and weaned piglets. K88 fimbrial adhesins are filamentous surface appendages whose lectin (carbohydrate-binding) activity allows K88 ETEC to attach to specific glycoconjugates (receptors) on porcine intestinal epithelial cells. There are three variants of K88 adhesin (K88ab, K88ac, and K88ad), which possess different, yet related, carbohydrate-binding specificities. We used porcine serum transferrin (pSTf) and purified glycosphingolipids (GSL) to begin to define the minimal recognition sequence for K88 adhesin variants. We found that K88ab adhesin binds with high affinity to pSTf (dissociation constant, 75 μM), while neither K88ac nor K88ad adhesin recognizes pSTf. Degradation of the N-glycan on pSTf by extensive metaperiodate treatment abolished its interaction with the K88ab adhesin, indicating that the K88ab adhesin binds to the single N-glycan found on pSTf. Using exoglycosidase digestion of the pSTf glycan, we demonstrated that K88ab adhesin recognizesN-acetylglucosamine (GlcNAc) residues in the core of the N-glycan on pSTf. All three K88 variants were found to bind preferentially to GSL containing a β-linkedN-acetylhexosamine (HexNAc), either GlcNAc orN-acetylgalactosamine, in the terminal position or, alternatively, in the penultimate position with galactose in the terminal position. Considering the results from pSTf and GSL binding studies together, we propose that the minimal recognition sequence for the K88 adhesin variants contains a β-linked HexNAc. In addition, the presence of a terminal galactose β-linked to this HexNAc residue enhances K88 adhesin binding.
rgf
Encodes a Novel Two-Component Signal Transduction System of
Streptococcus agalactiae
Authors: Spellerberg Barbara , Rozdzinski Eva , Martin Simone , Weber-Heynemann Josefine , Lütticken Rudolf 
Published: July 2002

ABSTRACT

The adhesion of gram-positive bacteria to extracellular matrix (ECM) proteins is regarded as an important determinant of pathogenicity. A comparison of the adhesion of
Streptococcus agalactiae
strain O90R to different ECM proteins showed that the most pronounced binding could be observed for immobilized fibrinogen. To investigate the genetic determinants of
S. agalactiae
fibrinogen binding, a pGhost9:IS
S1
mutant library was screened for mutants displaying reduced agglutination of fibrinogen-coated latex beads. A putative two-component signal transduction system was identified and designated
rgfBDAC
. It comprises genes encoding a putative response regulator of 218 amino acids and a putative histidine kinase of 426 amino acids. Comparison of the deduced proteins with the GenBank database revealed a significant similarity to quorum-sensing systems of gram-positive pathogens. Transcription analysis of the
rgf
locus showed that the encoding genes are located on one transcript. To further characterize the influence of the putative histidine kinase encoded in the
rgf
locus on the adhesion of
S. agalactiae
to immobilized fibrinogen, a targeted mutant of
rgfC
was generated. In comparison to the wild-type strain this mutant demonstrated altered fibrinogen binding capacities depending on bacterial cell density. Transcription analysis of secreted and surface-localized
S. agalactiae
proteins in the wild type and the
rgfC
mutant strain revealed that mRNA levels of the C5a peptidase gene
scpB
were increased in the mutant strain while the transcription of the secreted CAMP factor gene
cfb
was unaffected by this mutation. Based on these results, we hypothesize that
rgf
regulates the expression of bacterial cell surface components.
Enhanced Disease Severity inHelicobacter pylori-Infected Mice Deficient in Fas Signaling
Authors: Jones Nicola L. , Day Andrew S. , Jennings Hilary , Shannon Patrick T. , Galindo-Mata Esther , Sherman Philip M. 
Published: July 2002

ABSTRACTRecent evidence suggests that immune-mediated gastric epithelial cell apoptosis through Fas-Fas ligand interactions participates inHelicobacter pyloridisease pathogenesis. To define the role of Fas signaling in vivo,H. pyloristrain SS1 infection in C57BL/6 mice was compared to that in mice deficient in the Fas ligand (gld).gldmice had a degree of gastritis similar to that of C57BL/6 mice after 6 weeks (gastritis score, 5.2 ± 0.6 [mean ± standard error] versus 3.5 ± 0.8) and 12 weeks (4.0 ± 0.7 versus 3.4 ± 0.5) of infection. Bacterial colonization was comparable in each group of mice at 12 weeks of infection (2.1 ± 0.3 versus 1.6 ± 0.3 forgldand C57BL/6, respectively; the difference is not significant). Sixty-seven percent ofH. pylori-infectedgldmice displayed atrophic changes in the gastric mucosa, compared with 37% of infected C57BL/6 mice, at 12 weeks. In addition, atrophic changes were more severe inH. pylori-infectedgldmice (P< 0.05). Splenocytes isolated fromH. pylori-infected C57BL/6 mice had a twofold increase in production of the Th1 cytokine gamma interferon (IFN-γ) in response toH. pyloriantigens at both 6 and 12 weeks compared to controls (143 ± 65 versus 69 ±26 pg/ml and 336 ± 73 versus 172 ± 60, respectively). In contrast, there was a lack of detectable IFN-γ ingldmice infected with the bacterium.H. pylori-infected C57BL/6 mice had increased epithelial cell apoptosis compared with sham-infected C57BL/6 mice (35.0 ± 8.9 versus 12.3 ± 6.9;P< 0.05). Epithelial cell apoptosis did not differ betweenH. pylori-infected and controlgldmice (5.2 ± 1.6 versus 6.5 ± 2.9 [not significant]). These data demonstrate that mice with mutations in the Fas ligand develop more severe premalignant mucosal changes in response to infection withH. pyloriin association with both an impaired gastric epithelial cell apoptotic response and IFN-γ production. The Fas death pathway modulates disease pathophysiology following murine infection withH. pylori. Deregulation of the Fas pathway could be involved in the transition from gastritis to gastric cancers duringH. pyloriinfection.
Characterization of an Extracellular Lipase Encoded by
LIP2
in
Yarrowia lipolytica
Authors: Pignède Georges , Wang Huijie , Fudalej Franck , Gaillardin Claude , Seman Michel , Nicaud Jean-Marc 
Published: July 2002

ABSTRACT

We isolated the
LIP2
gene from the lipolytic yeast
Yarrowia lipolytica
. It was found to encode a 334-amino-acid precursor protein. The secreted lipase is a 301-amino-acid glycosylated polypeptide which is a member of the triacylglycerol hydrolase family (EC
3.1.1.3
). The Lip2p precursor protein is processed by the
KEX2
-like endoprotease encoded by
XPR6
. Deletion of the
XPR6
gene resulted in the secretion of an active but less stable proenzyme. Thus, the pro region does not inhibit lipase secretion and activity. However, it does play an essential role in the production of a stable enzyme. Processing was found to be correct in
LIP2
A
(multiple
LIP2
copy integrant)-overexpressing strains, which secreted 100 times more activity than the wild type, demonstrating that
XPR6
maturation was not limiting. No extracellular lipase activity was detected with the
lip2
knockout (KO) strain, strongly suggesting that extracellular lipase activity results from expression of the
LIP2
gene. Nevertheless, the
lip2
KO strain is still able to grow on triglycerides, suggesting an alternative pathway for triglyceride utilization in
Y. lipolytica
.
Salmonella enterica
Serovar Typhimurium Peptidase B Is a Leucyl Aminopeptidase with Specificity for Acidic Amino Acids
Authors: Mathew Zacharia , Knox Tina M. , Miller Charles G. 
Published: July 2002

ABSTRACT

Peptidase B (PepB) of
Salmonella enterica
serovar Typhimurium is one of three broad-specificity aminopeptidases found in this organism. We have sequenced the
pepB
gene and found that it encodes a 427-amino-acid (46.36-kDa) protein, which can be unambiguously assigned to the leucyl aminopeptidase (LAP) structural family. PepB has been overexpressed and purified. The active enzyme shows many similarities to other members of the LAP family: it is a heat-stable (70°C; 20 min) hexameric (∼270-kDa) metallopeptidase with a pH optimum of 8.5 to 9.5. A detailed study of the substrate specificity of the purified protein shows that it differs from other members of the family in its ability to hydrolyze peptides with N-terminal acidic residues. The preferred substrates for PepB are peptides with N-terminal Asp or Glu residues. Comparison of the amino acid sequence of PepB with those of other LAPs leads to the conclusion that PepB is the prototype of a new LAP subfamily with representatives in several other eubacterial species and to the prediction that the members of this family share the ability to hydrolyze peptides with N-terminal acidic residues. Site-directed mutagenesis has been used to show that this specificity appears to be determined by a single Lys residue present in a sequence motif conserved in all members of the subfamily.
Identification of an Archaeal 2-Hydroxy Acid Dehydrogenase Catalyzing Reactions Involved in Coenzyme Biosynthesis in Methanoarchaea
Authors: Graupner Marion , Xu Huimin , White Robert H. 
Published: July 2002

ABSTRACT

Two putative malate dehydrogenase genes, MJ1425 and MJ0490, from
Methanococcus jannaschii
and one from
Methanothermus fervidus
were cloned and overexpressed in
Escherichia coli
, and their gene products were tested for the ability to catalyze pyridine nucleotide-dependent oxidation and reduction reactions of the following α-hydroxy–α-keto acid pairs: (
S
)-sulfolactic acid and sulfopyruvic acid; (
S
)-α-hydroxyglutaric acid and α-ketoglutaric acid; (
S
)-lactic acid and pyruvic acid; and 1-hydroxy-1,3,4,6-hexanetetracarboxylic acid and 1-oxo-1,3,4,6-hexanetetracarboxylic acid. Each of these reactions is involved in the formation of coenzyme M, methanopterin, coenzyme F
420
, and methanofuran, respectively. Both the MJ1425-encoded enzyme and the MJ0490-encoded enzyme were found to function to different degrees as malate dehydrogenases, reducing oxalacetate to (
S
)-malate using either NADH or NADPH as a reductant. Both enzymes were found to use either NADH or NADPH to reduce sulfopyruvate to (
S
)-sulfolactate, but the
V
max
/

K
m

value for the reduction of sulfopyruvate by NADH using the MJ1425-encoded enzyme was 20 times greater than any other combination of enzymes and pyridine nucleotides. Both the
M. fervidus
and the MJ1425-encoded enzyme catalyzed the NAD
+
-dependent oxidation of (
S
)-sulfolactate to sulfopyruvate. The MJ1425-encoded enzyme also catalyzed the NADH-dependent reduction of α-ketoglutaric acid to (
S
)-hydroxyglutaric acid, a component of methanopterin. Neither of the enzymes reduced pyruvate to (
S
)-lactate, a component of coenzyme F
420
. Only the MJ1425-encoded enzyme was found to reduce 1-oxo-1,3,4,6-hexanetetracarboxylic acid, and this reduction occurred only to a small extent and produced an isomer of 1-hydroxy-1,3,4,6-hexanetetracarboxylic acid that is not involved in the biosynthesis of methanofuran c. We conclude that the MJ1425-encoded enzyme is likely to be involved in the biosynthesis of both coenzyme M and methanopterin.
New Substrates for the Dicarboxylate Transport System of
Sinorhizobium meliloti
Authors: Yurgel Svetlana , Mortimer Michael W. , Rogers Kimberly N. , Kahn Michael L. 
Published: July 2002

ABSTRACT

The dicarboxylate transport (Dct) system of
Sinorhizobium meliloti
, which is essential for a functional nitrogen-fixing symbiosis, has been thought to transport only dicarboxylic acids. We show here that the permease component of the Dct system, DctA, can transport orotate, a monocarboxylic acid, with an apparent

K
m

of 1.7 mM and a
V
max
of 163 nmol min
−1
per mg of protein in induced cells. DctA was not induced by the presence of orotate. The transport of orotate was inhibited by several compounds, including succinamic acid and succinamide, which are not dicarboxylic acids. The dicarboxylic acid maleate (
cis
-butenedioic acid) was not an inhibitor of orotate transport, which suggests that it was not recognized by DctA. However, maleate was an excellent inducer of DctA expression. Our evaluation of 17 compounds as inducers and inhibitors of transport suggests that substrates recognized by
S. meliloti
DctA must have appropriately spaced carbonyl groups and an extended conformation, while good inducers are more likely to have a curved conformation.
Developmental Regulation of the Cell Division Protein FtsZ in
Anabaena
sp. Strain PCC 7120, a Cyanobacterium Capable of Terminal Differentiation
Authors: Kuhn Isabelle , Peng Ling , Bedu Sylvie , Zhang Cheng-Cai 
Published: July 2002

ABSTRACT

Heterocysts are terminally differentiated cells devoted to nitrogen fixation in the filamentous cyanobacterium
Anabaena
sp. strain PCC 7120. We show here that the cell division protein FtsZ is present in vegetative cells but undetectable in heterocysts. These results provide a first rational explanation for the inability of mature heterocysts to undergo cell division.
Genetic Analysis of a Gene Cluster for Cyclohexanol Oxidation in
Acinetobacter
sp. Strain SE19 by In Vitro Transposition
Authors: Cheng Qiong , Thomas Stuart M. , Kostichka Kristy , Valentine James R. , Nagarajan Vasantha 
Published: July 2002

ABSTRACT

Biological oxidation of cyclic alcohols normally results in formation of the corresponding dicarboxylic acids, which are further metabolized and enter the central carbon metabolism in the cell. We isolated an
Acinetobacter
sp. from an industrial wastewater bioreactor that utilized cyclohexanol as a sole carbon source. A cosmid library was constructed from
Acinetobacter
sp. strain SE19, and oxidation of cyclohexanol to adipic acid was demonstrated in recombinant
Escherichia coli
carrying a SE19 DNA segment. A region that was essential for cyclohexanol oxidation was localized to a 14-kb fragment on the cosmid DNA. Several putative open reading frames (ORFs) that were expected to encode enzymes catalyzing the conversion of cyclohexanol to adipic acid were identified. Whereas one ORF showed high homology to cyclohexanone monooxygenase from
Acinetobacter
sp. strain NCIB 9871, most of the ORFs showed only moderate homology to proteins in GenBank. In order to assign functions of the various ORFs, in vitro transposon mutagenesis was performed using the cosmid DNA as a target. A set of transposon mutants with a single insertion in each of the ORFs was screened for cyclohexanol oxidation in
E. coli
. Several of the transposon mutants accumulated a variety of cyclohexanol oxidation intermediates. The in vitro transposon mutagenesis technique was shown to be a powerful tool for rapidly assigning gene functions to all ORFs in the pathway.