bluuebunny/crossref_metadata_2025_split huggingface dataset:
The pH of the Host Niche Controls Gene Expression in and Virulence of
Candida albicans
Authors: De Bernardis Flavia , Mühlschlegel Fritz A. , Cassone Antonio , Fonzi William A. 
Published: December 2019

ABSTRACT

Little is known of the biological attributes conferring pathogenicity on the opportunistic fungal pathogen
Candida albicans
. Infection by this pathogen, as for bacterial pathogens, may rely upon environmental signals within the host niche to regulate the expression of virulence determinants. To determine if
C. albicans
responds to the pH of the host niche, we tested the virulence of strains with mutations in either of two pH-regulated genes,
PHR1
and
PHR2
. In vitro,
PHR1
is expressed when the ambient pH is at 5.5 or higher and deletion of the gene results in growth and morphological defects at neutral to alkaline pHs. Conversely,
PHR2
is expressed at an ambient pH below 5.5, and the growth and morphology of the null mutant is compromised below this pH. A
PHR1
null mutant was avirulent in a mouse model of systemic infection but uncompromised in its ability to cause vaginal infection in rats. Since systemic pH is near neutrality and vaginal pH is around 4.5, the virulence phenotype paralleled the pH dependence of the in vitro phenotypes. The virulence phenotype of a
PHR2
null mutant was the inverse. The mutant was virulent in a systemic-infection model but avirulent in a vaginal-infection model. Heterozygous mutants exhibited partial reductions in their pathogenic potential, suggesting a gene dosage effect. Unexpectedly, deletion of
PHR2
did not prevent hyphal development in vaginal tissue, suggesting that it is not essential for hyphal development in this host niche. The results suggest that the pH of the infection site regulates the expression of genes essential to survival within that niche. This implies that the study of environmentally regulated genes may provide a rationale for understanding the pathobiology of
C. albicans
.
Cloning and Mutagenesis of a Serotype-Specific DNA Region Involved in Encapsulation and Virulence ofActinobacillus pleuropneumoniaeSerotype 5a: Concomitant Expression of Serotype 5a and 1 Capsular Polysaccharides in RecombinantA. pleuropneumoniaeSerotype 1
Authors: Ward Christine K. , Lawrence Mark L. , Veit Hugo P. , Inzana Thomas J. 
Published: December 2019

ABSTRACTA DNA region involved inActinobacillus pleuropneumoniaeserotype 5 capsular polysaccharide (CP) biosynthesis was identified and characterized by using a probe specific for thecpxDgene involved in CP export. The adjacent serotype 5-specific CP biosynthesis region was cloned from a 5.8-kbBamHI fragment and an 8.0-kbEcoRI fragment of strain J45 genomic DNA. DNA sequence analysis demonstrated that this region contained four complete open reading frames,cps5A,cps5B,cps5C, andcps5D. Cps5A, Cps5B, and Cps5C showed low homology with several bacterial glycosyltransferases involved in the biosynthesis of lipopolysaccharide or CP. However, Cps5D had high homology with KdsA proteins (3-deoxy-d-manno-2-octulosonic acid 8-phosphate synthetase) from other gram-negative bacteria. The G+C content ofcps5ABCwas substantially lower (28%) than that ofcps5Dand the rest of theA. pleuropneumoniaechromosome (42%). A 2.1-kb deletion spanning the clonedcps5ABCopen reading frames was constructed and transferred into the J45 chromosome by homologous recombination with a kanamycin resistance cassette to produce mutant J45-100. Multiplex PCR confirmed the deletion in this region of J45-100 DNA. J45-100 did not produce intracellular or extracellular CP, indicating thatcps5A,cps5B, and/orcps5Cwere involved in CP biosynthesis. However, biosynthesis of the Apx toxins, lipopolysaccharide, and membrane proteins was unaffected by the mutation. Besides lack of CP biosynthesis, and in contrast to J45, J45-100 grew faster, was sensitive to killing in precolostral calf serum, and was avirulent in pigs at an intratracheal challenge dose three times the 50% lethal dose (LD50) of strain J45. At six times the J45 LD50, J45-100 caused mild to moderate lung lesions but not death. Electroporation ofcps5ABCintoA. pleuropneumoniaeserotype 1 strain 4074 generated strain 4074(pJMLCPS5), which expressed both serotype 1 and serotype 5 CP. However, serotype 1 capsule expression was diminished in 4074(pJMLCPS5) in comparison to 4074. The recombinant strain produced significantly less total CP (serotypes 1 and 5 CP combined) in log phase (P= 0.0012) but significantly more total CP in late stationary phase than 4074 (P< 0.0001). In addition, strain 4074(pJMLCPS5) caused less mortality and bacteremia in pigs and mice following respiratory challenge than strain 4074, indicating that virulence was affected by diminished capsule production. These results emphasize the importance of CP in the serum resistance and virulence ofA. pleuropneumoniae.
Cytotoxicity of Hemolytic, Cytotoxic Necrotizing Factor 1-Positive and -Negative
Escherichia coli
to Human T24 Bladder Cells
Authors: Island Michael D. , Cui Xiaoling , Foxman Betsy , Marrs Carl F. , Stamm Walter E. , Stapleton Ann E. , Warren John W. 
Published: December 2019

ABSTRACT

Approximately one-half of
Escherichia coli
isolates from patients with cystitis or pyelonephritis produce the pore-forming cytotoxin hemolysin, a molecule with the capacity to lyse erythrocytes and a range of nucleated cell types. A second toxin, cytotoxic necrotizing factor 1 (CNF1), is found in approximately 70% of hemolytic, but rarely in nonhemolytic, isolates. To evaluate the potential interplay of these two toxins, we used epidemiological and molecular biologic techniques to compare the cytotoxicity of hemolytic, CNF1
+
, and CNF1
−
cystitis strains toward human T24 bladder epithelial cells in vitro. A total of 29 isolates from two collections of cystitis-associated
E. coli
were evaluated by using methylene blue staining of bladder monolayers at 1-h intervals after inoculation with each strain. Most (20 of 29) isolates damaged or destroyed the T24 monolayer (less than 50% remaining) within 4 h after inoculation. As a group, CNF1
+
isolates from one collection (11 strains) were less cytotoxic at 4 h than the CNF1
−
strains in that collection (
P
= 0.009), but this pattern was not observed among isolates from the second collection (18 strains). To directly evaluate the role of CNF1 in cytotoxicity of hemolytic
E. coli
without the variables present in multiple clinical isolates, we constructed mutants defective in production of CNF1. Compared to the CNF1
+
parental isolates, no change in cytotoxicity was detected in these
cnf1
mutants. Our results indicate that CNF1 does not have a detectable effect on the ability of hemolytic
E. coli
to damage human bladder cell monolayers in vitro.
Monocytic Differentiation Inhibits Infection and Granulocytic Differentiation Potentiates Infection by the Agent of Human Granulocytic Ehrlichiosis
Authors: Klein Marina B. , Hayes Stanley F. , Goodman Jesse L. 
Published: December 2019

ABSTRACT

Human granulocytic ehrlichiosis (HGE) is an emerging tick-borne infection with a specific tropism for granulocytes. We previously isolated and cultivated the HGE agent in the promyelocytic leukemia cell line HL-60 and have also demonstrated the susceptibility of both granulocytic and monocytic human marrow progenitors. Circulating monocytes have not been observed to be infected, suggesting that cell susceptibility may be differentiation specific. To evaluate this hypothesis, HL-60 cells were differentiated towards granulocytes (with dimethyl sulfoxide or all-
trans
retinoic acid) or toward monocytes-macrophages (with 12-
O
-tetradecanoylphorbol-13-acetate [TPA], gamma interferon, or 1,25-dihydroxyvitamin D
3
) and then challenged with HGE. HGE binding, internalization, and proliferation were compared in differentiated and untreated control HL-60 cells by immunofluorescence, electron microscopy, and Giemsa staining. Granulocytic differentiation resulted in a doubling of HGE binding and enhanced infection consistent with the agent’s clinical tropism for neutrophils. Granulocytic cells were unable to kill internalized ehrlichiae even after activation induced by
N
-formyl-Met-Leu-Phe alone or together with tumor necrosis factor alpha. In contrast, monocyte-macrophage differentiation with TPA resulted in complete resistance to infection through at least two distinct mechanisms: (i) reduction in binding and uptake and (ii) killing of any internalized organisms. Diminished binding in TPA-treated cells correlated with their reduced expression of sialyl Lewis x (CD15s), a putative cellular receptor component for HGE. The degree of monocytic differentiation and activation induced (i.e., TPA > gamma interferon > vitamin D
3
) correlated with resistance to HGE. Thus, HL-60 cells exhibit a striking differentiation-specific susceptibility to HGE. Differentiation-induced changes in bacterial adhesion and killing capacity underlie the tropism of HGE for granulocytic HL-60 cells and, conversely, the resistance of activated macrophages to infection.
Attachment of
Cryptosporidium parvum
Sporozoites to Human Intestinal Epithelial Cells
Authors: Joe Angela , Verdon Renaud , Tzipori Saul , Keusch Gerald T. , Ward Honorine D. 
Published: December 2019

ABSTRACT

An enzyme-linked immunosorbent assay-based attachment model using the human intestinal cell line Caco-2A was developed to study attachment of
Cryptosporidium parvum
sporozoites in vitro and to assess potential inhibitors of sporozoite binding. In this system, attachment was related to sporozoite dose, incubation time, and host cell differentiation status. Polyclonal antibodies to
C. parvum
as well as glycoprotein inhibitors of a sporozoite lectin reduced attachment. This model will be a valuable tool in elucidating specific molecules and mechanisms involved in sporozoite-host cell attachment.
Tube Phagocytosis, a Novel Way for Neutrophils To Phagocytize
Borrelia burgdorferi
Authors: Suhonen Juha , Hartiala Kaija , Viljanen Matti K. 
Published: December 2019

ABSTRACT

Interactions between human neutrophils and
Borrelia burgdorferi
, the Lyme disease spirochete, were studied by dark-field microscopy combined with video technology. A previously unrecognized mechanism for neutrophils to phagocytize the spirochete was discovered. During phagocytosis, the spirochete attaches to the neutrophil head-on, the neutrophil forms a thin tubelike protrusion around the bacterium, and the fully covered spirochete is drawn into the cell.
Susceptibility of Epithelial Cells to
Pseudomonas aeruginosa
Invasion and Cytotoxicity Is Upregulated by Hepatocyte Growth Factor
Authors: Fleiszig Suzanne M. J. , Vallas Vicky , Jun Cindy H. , Mok Leo , Balkovetz Daniel F. , Roth Michael G. , Mostov Keith E. 
Published: December 2019

ABSTRACT

Normal cell polarity protects epithelial cells against
Pseudomonas aeruginosa
invasion and cytotoxicity. Using epithelial cell clones with selective defects in sorting of membrane constituents, and using hepatocyte growth factor pretreatment, we found that polarized susceptibility to
P. aeruginosa
can be altered without disrupting tight junctions. The results also showed that cellular susceptibility factors for invasion and cytotoxicity are not the same, although both are localized to the basolateral cell surface in polarized epithelial cells.
Delayed-Type Hypersensitivity Responses to ESAT-6 and MPT64 fromMycobacterium tuberculosisin the Guinea Pig
Authors: Elhay Martin J. , Oettinger Thomas , Andersen Peter 
Published: December 2019

ABSTRACTTwo antigens fromMycobacterium tuberculosis, ESAT-6 and MPT64, elicited delayed-type hypersensitivity (DTH) skin responses in outbred guinea pigs infected withM. tuberculosisby the aerosol and intravenous routes but not those sensitized withM. bovisBCG orM. avium. The DTH epitope of ESAT-6 was mapped to the C terminus. Nonresponders to the individual antigens were found, but all animals responded to a combination of ESAT-6 and MPT64 or their respective minimal target peptides. Correspondingly, these molecules could form the basis of a new skin test for tuberculosis.
Role of a Cytotoxic Enterotoxin in
Aeromonas
-Mediated Infections: Development of Transposon and Isogenic Mutants
Authors: Xu Xin-J. , Ferguson M. R. , Popov V. L. , Houston C. W. , Peterson J. W. , Chopra A. K. 
Published: December 2019

ABSTRACT

Transposon and marker exchange mutagenesis were used to evaluate the role of
Aeromonas
cytotoxic enterotoxin (Act) in the pathogenesis of diarrheal diseases and deep wound infections. The transposon mutants were generated by random insertion of Tn
5-751
in the chromosomal DNA of a diarrheal isolate SSU of
Aeromonas hydrophila
. Some of the transposon mutants had dramatically reduced hemolytic and cytotoxic activities, and such mutants exhibited reduced virulence in mice compared to wild-type
Aeromonas
when injected intraperitoneally (i.p.). Southern blot data indicated that transposition in these mutants did not occur within the cytotoxic enterotoxin gene (
act
). The transcription of the
act
gene was affected drastically in the transposon mutants, as revealed by Northern blot analysis. The altered virulence of these transposon mutants was confirmed by developing isogenic mutants of the wild-type
Aeromonas
by using a suicide vector. In these mutants, the truncated
act
gene was integrated in place of a functionally active
act
gene. The culture filtrates from isogenic mutants were devoid of hemolytic, cytotoxic, and enterotoxic activities associated with Act. These filtrates caused no damage to mouse small intestinal epithelium, as determined by electron microscopy, whereas culture filtrates from wild-type
Aeromonas
caused complete destruction of the microvilli. The 50% lethal dose of these mutants in mice was 1.0 × 10
8
when injected i.p., compared to 3.0 × 10
5
for the wild-type
Aeromonas
. Reintegration of the native
act
gene in place of the truncated toxin gene in isogenic mutants resulted in complete restoration of Act’s biological activity and virulence in mice. The animals injected with a sublethal dose of wild-type
Aeromonas
or the revertant, but not the isogenic mutant, had circulating toxin-specific neutralizing antibodies. Taken together, these studies clearly established a role for Act in the pathogenesis of
Aeromonas
-mediated infections.
CD1 Presents Antigens from a Gram-Negative Bacterium,Haemophilus influenzaeType b
Authors: Fairhurst Rick M. , Wang Chun X. , Sieling Pete A. , Modlin Robert L. , Braun Jonathan 
Published: December 2019

ABSTRACTHuman CD1 is a family of nonpolymorphic major histocompatibility complex class I-like molecules capable of presenting mycobacterial lipids, including lipoarabinomannan (LAM), to double-negative (DN; CD4−CD8−) as well as CD8+T cells. Structural similarities between LAM and the capsular polysaccharides of gram-negative bacteria led us to consider the latter as candidate CD1 ligands. We derived two CD1-restricted DN T-cell populations which proliferated toHaemophilus influenzaetype b (Hib) antigen. One T-cell population also proliferated to proteinase K-treated Hib antigen, suggesting that it recognized a nonpeptide. Our work thus expands the universe of T cell antigens to include nonpeptides distinct from mycobacterial lipids and suggests a potential role for CD1-restricted T cells in immunity to Hib.
Levels of Inhibitors of Tumor Necrosis Factor Alpha and Interleukin 1β in Urine and Sera of Patients with Urosepsis
Authors: Olszyna Dariusz P. , Prins Jan M. , Buis Barbara , van Deventer Sander J. H. , Speelman Peter , van der Poll Tom 
Published: December 2019

ABSTRACTThe antiinflammatory cytokine response during urosepsis was determined by measurement of concentrations of soluble tumor necrosis factor receptor (sTNFR) types I and II, interleukin 1 receptor antagonist (IL-1ra), soluble IL-1 receptor type II (sIL-1RII), and interleukin 10 in sera and urine of 30 patients with culture-proven urinary tract infections before and 4, 24, 48, and 72 h after initiation of antibiotic therapy and in 20 healthy individuals. In serum, the levels of sTNFR types I and II, IL-1ra, and IL-10 were higher in patients than in controls. In urine, only sTNFR type I and II levels were elevated in patients. The ratios of concentrations of both types of sTNFR in urine to concentrations in serum were higher in patients than in controls. These findings indicate that during urosepsis, the antiinflammatory cytokine response is generated predominantly at the systemic level.
Lipopolysaccharides from
Campylobacter jejuni
O:41 Strains Associated with Guillain-Barré Syndrome Exhibit Mimicry of GM
1
Ganglioside
Authors: Prendergast Martina M. , Lastovica Albert J. , Moran Anthony P. 
Published: December 2019

ABSTRACT

Three
Campylobacter jejuni
, biotype 2, serotype O:41 strains that were isolated from patients who developed Guillain-Barré syndrome (GBS) and one
C. jejuni
isolate from a patient who developed enteritis only were examined. The aim of the study was to determine the structure of the core oligosaccharide (OS) of the lipopolysaccharide (LPS) of
C. jejuni
serotype O:41, a serotype rarely associated with the development of GBS, and to determine if the LPS shares similar epitopes with any of the major human gangliosides. Electrophoretic analysis with silver staining or immunoblotting demonstrated that the strains had LPS profiles characteristic of low-molecular-weight LPS. Colorimetric analysis detected
N
-acetylneuraminic (sialic) acid in the core OSs of all the strains. Thin-layer chromatography with immunostaining showed that antisera raised against the GBS strains reacted with the GM
1
ganglioside, suggesting that
C. jejuni
serotype O:41 LPSs and the GM
1
ganglioside have similar epitopes. Furthermore, polyclonal anti-GM
1
and anti-asialoGM
1
antibodies cross-reacted with each
C. jejuni
O:41 LPS tested, suggesting that the serotype O:41 core OS has a GM
1
- and asialoGM
1
-like structure. LPSs extracted from
C. jejuni
serostrains O:2, O:3, and O:19 were also used in the study. Cholera toxin (a GM
1
ligand) and peanut agglutinin (a Galβ1–3GalNAc ligand) recognized all serotype O:41 LPSs and the serostrain O:2 LPS. Immunoadsorption results confirmed GM
1
relatedness. Moreover, the core OS was isolated from a GBS-associated
C. jejuni
O:41 LPS by gel permeation chromatography. An analysis by gas-liquid chromatography (GLC), GLC-mass spectrometry, and nuclear magnetic resonance showed the core OS of one of the
C. jejuni
O:41 GBS isolates to have a tetrasaccharide structure consistent with GM
1
mimicry.
Listeria monocytogenesStimulates Mucus Exocytosis in Cultured Human Polarized Mucosecreting Intestinal Cells through Action of Listeriolysin O
Authors: Coconnier Marie-Hélène , Dlissi Elyess , Robard Myriam , Laboisse Christian L. , Gaillard Jean-Louis , Servin Alain L. 
Published: December 2019

ABSTRACTWhen the intracellular pathogenListeria monocytogenesinfects cultured human mucosecreting polarized HT29-MTX cells apically, it induces the stimulation of mucus exocytosis without cell entry. Using a set of isogenic mutants and purified listeriolysin O (LLO), we identified theL. monocytogenesthiol-activated exotoxin LLO as the agonist of mucus secretion. We demonstrated that the LLO-induced mucus exocytosis did not result from the LLO membrane-damaging activity. We found that LLO-induced mucus exocytosis is an event requiring the binding of LLO to a brush border-associated receptor and membrane oligomerization of the exotoxin. By a pharmacological approach, we demonstrated that no regulatory system or intracellular transducing signal known to be involved in control of mucin exocytosis was activated by LLO. Based on the present data, the stimulatory action of LLO on mucin exocytosis could be accounted for either by an unknown signaling system which remains to be determined or by direct action of LLO with the membrane vesicle components involved in the intracellular vesicular transport of mucins.
Kinetics and In Vivo Induction of Genetic Variation of
vlsE
in
Borrelia burgdorferi
Authors: Zhang Jing-Ren , Norris Steven J. 
Published: December 2019

ABSTRACT

The Lyme disease agent,
Borrelia burgdorferi
, is able to persistently infect humans and animals for months or years in the presence of an active immune response. It is not known how the organisms survive immune attack in the mammalian host.
vlsE
, a gene localized near one end of linear plasmid lp28-1 and encoding a surface-exposed lipoprotein in
B. burgdorferi
B31, was shown recently to undergo extensive genetic and antigenic variation within 28 days of initial infection in C3H/HeN mice. In this study, we examined the kinetics of
vlsE
sequence variation in C3H/HeN mice at 4, 7, 14, 21, and 28 days and at 7 and 12 months postinfection. Sequence changes were detected by PCR amplification and sequence analysis as early as 4 days postinfection and accumulated progressively in both C3H/HeN and CB-17 severe combined immunodeficient (SCID) mice throughout the course of infection. The sequence changes were consistent with sequential recombination of segments from multiple silent
vls
cassette sites into the
vlsE
expression site. No
vlsE
sequence changes were detected in organisms cultured in vitro for up to 84 days. These results indicate that
vlsE
recombination is induced by a factor(s) present in the mammalian host, independent of adaptive immune responses. The possible inducing conditions appear to be present in various tissue sites because isolates from multiple tissues showed similar degrees of sequence variation. The rate of accumulation of predicted amino acid changes was higher in the immunologically intact C3H/HeN mice than in SCID mice, a finding consistent with immune selection of VlsE variants.
Genetic Variation of the
Borrelia burgdorferi
Gene
vlsE
Involves Cassette-Specific, Segmental Gene Conversion
Authors: Zhang Jing-Ren , Norris Steven J. 
Published: December 2019

ABSTRACT

The Lyme disease spirochete
Borrelia burgdorferi
possesses 15 silent
vls
cassettes and a
vls
expression site (
vlsE
) encoding a surface-exposed lipoprotein. Segments of the silent
vls
cassettes have been shown to recombine with the
vlsE
cassette region in the mammalian host, resulting in combinatorial antigenic variation. Despite promiscuous recombination within the
vlsE
cassette region, the 5′ and 3′ coding sequences of
vlsE
that flank the cassette region are not subject to sequence variation during these recombination events. The segments of the silent
vls
cassettes recombine in the
vlsE
cassette region through a unidirectional process such that the sequence and organization of the silent
vls
loci are not affected. As a result of recombination, the previously expressed segments are replaced by incoming segments and apparently degraded. These results provide evidence for a gene conversion mechanism in VlsE antigenic variation.