bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heteroresistance to Itraconazole Alters the Morphology and Increases the Virulence of Cryptococcus gattii
Authors: Ferreira Gabriella Freitas , Santos Julliana Ribeiro Alves , Costa Marliete Carvalho da , Holanda Rodrigo Assunção de , Denadai Ângelo Márcio Leite , Freitas Gustavo José Cota de , Santos Áquila Rodrigues Costa , Tavares Priscila Batista , Paixão Tatiane Alves , Santos Daniel Assis 
Published: May 2015

ABSTRACT

Cryptococcus gattii
is the main etiological agent of cryptococcosis in immunocompetent individuals. The triazole drug itraconazole is one of the antifungals used to treat patients with cryptococcosis. Heteroresistance is an adaptive mechanism to counteract the stress of increasing drug concentrations, and it can enhance the ability of a microorganism to survive under antifungal pressure. In this study, we evaluated the ability of 11
C. gattii
strains to develop itraconazole heteroresistance. Heteroresistant clones were analyzed for drug susceptibility, alterations in cell diameter, capsule properties, and virulence in a murine model. Heteroresistance to itraconazole was intrinsic in all of the strains analyzed, reduced both the capsule size and the cell diameter, induced molecular heterogeneity at the chromosomal level, changed the negatively charged cells, reduced ergosterol content, and improved the antioxidant system. A positive correlation between surface/volume ratio of original cells and the level of heteroresistance to itraconazole (LHI) was observed in addition to a negative correlation between capsule size of heteroresistant clones and LHI. Moreover, heteroresistance to itraconazole increased the engulfment of
C. gattii
by macrophages and augmented fungal proliferation inside these cells, which probably accounted for the reduced survival of the mice infected with the heteroresistant clones and the higher fungal burden in lungs and brain. Our results indicate that heteroresistance to itraconazole is intrinsic and increases the virulence of
C. gattii
. This phenomenon may represent an additional mechanism that contributes to relapses of cryptococcosis in patients during itraconazole therapy.
Azole Antifungal Agents To Treat the Human Pathogens Acanthamoeba castellanii and Acanthamoeba polyphaga through Inhibition of Sterol 14α-Demethylase (CYP51)
Authors: Lamb David C. , Warrilow Andrew G. S. , Rolley Nicola J. , Parker Josie E. , Nes W. David , Smith Stephen N. , Kelly Diane E. , Kelly Steven L. 
Published: May 2015

ABSTRACTIn this study, we investigate the amebicidal activities of the pharmaceutical triazole CYP51 inhibitors fluconazole, itraconazole, and voriconazole againstAcanthamoeba castellaniiandAcanthamoeba polyphagaand assess their potential as therapeutic agents againstAcanthamoebainfections in humans. Amebicidal activities of the triazoles were assessed byin vitrominimum inhibition concentration (MIC) determinations using trophozoites ofA. castellaniiandA. polyphaga. In addition, triazole effectiveness was assessed by ligand binding studies and inhibition of CYP51 activity of purifiedA. castellaniiCYP51 (AcCYP51) that was heterologously expressed inEscherichia coli. Itraconazole and voriconazole bound tightly to AcCYP51 (dissociation constant [Kd] of 10 and 13 nM), whereas fluconazole bound weakly (Kdof 2,137 nM). Both itraconazole and voriconazole were confirmed to be strong inhibitors of AcCYP51 activity (50% inhibitory concentrations [IC50] of 0.23 and 0.39 μM), whereas inhibition by fluconazole was weak (IC50, 30 μM). However, itraconazole was 8- to 16-fold less effective (MIC, 16 mg/liter) at inhibitingA. polyphagaandA. castellaniicell proliferation than voriconazole (MIC, 1 to 2 mg/liter), while fluconazole did not inhibitAcanthamoebacell division (MIC, >64 mg/liter)in vitro. Voriconazole was an effective inhibitor of trophozoite proliferation forA. castellaniiandA. polyphaga; therefore, it should be evaluated in trials versus itraconazole for controllingAcanthamoebainfections.
Limited Ability of Posaconazole To Cure both Acute and Chronic Trypanosoma cruzi Infections Revealed by Highly Sensitive
In Vivo
Imaging
Authors: Francisco Amanda Fortes , Lewis Michael D. , Jayawardhana Shiromani , Taylor Martin C. , Chatelain Eric , Kelly John M. 
Published: May 2015

ABSTRACT

The antifungal drug posaconazole has shown significant activity against
Trypanosoma cruzi
in vitro
and in experimental murine models. Despite this, in a recent clinical trial it displayed limited curative potential. Drug testing is problematic in experimental Chagas disease because of difficulties in demonstrating sterile cure, particularly during the chronic stage of infection when parasite burden is extremely low and tissue distribution is ill defined. To better assess posaconazole efficacy against acute and chronic Chagas disease, we have exploited a highly sensitive bioluminescence imaging system which generates data with greater accuracy than other methods, including PCR-based approaches. Mice inoculated with bioluminescent
T. cruzi
were assessed by
in vivo
and
ex vivo
imaging, with cyclophosphamide-induced immunosuppression used to enhance the detection of relapse. Posaconazole was found to be significantly inferior to benznidazole as a treatment for both acute and chronic
T. cruzi
infections. Whereas 20 days treatment with benznidazole was 100% successful in achieving sterile cure, posaconazole failed in almost all cases. Treatment of chronic infections with posaconazole did however significantly reduce infection-induced splenomegaly, even in the absence of parasitological cure. The imaging-based screening system also revealed that adipose tissue is a major site of recrudescence in mice treated with posaconazole in the acute, but not the chronic stage of infection. This
in vivo
screening model for Chagas disease is predictive, reproducible and adaptable to diverse treatment schedules. It should provide greater assurance that drugs are not advanced prematurely into clinical trial.
The Monoterpene Carvacrol Generates Endoplasmic Reticulum Stress in the Pathogenic Fungus Candida albicans
Authors: Chaillot Julien , Tebbji Faiza , Remmal Adnane , Boone Charlie , Brown Grant W. , Bellaoui Mohammed , Sellam Adnane 
Published: May 2015

ABSTRACT

The monoterpene carvacrol, the major component of oregano and thyme oils, is known to exert potent antifungal activity against the pathogenic yeast
Candida albicans
. This monoterpene has been the subject of a considerable number of investigations that uncovered extensive pharmacological properties, including antifungal and antibacterial effects. However, its mechanism of action remains elusive. Here, we used integrative chemogenomic approaches, including genome-scale chemical-genetic and transcriptional profiling, to uncover the mechanism of action of carvacrol associated with its antifungal property. Our results clearly demonstrated that fungal cells require the unfolded protein response (UPR) signaling pathway to resist carvacrol. The mutants most sensitive to carvacrol in our genome-wide competitive fitness assay in the yeast
Saccharomyces cerevisiae
expressed mutations of the transcription factor Hac1 and the endonuclease Ire1, which is required for Hac1 activation by removing a nonconventional intron from the 3′ region of
HAC1
mRNA. Confocal fluorescence live-cell imaging revealed that carvacrol affects the morphology and the integrity of the endoplasmic reticulum (ER). Transcriptional profiling of pathogenic yeast
C. albicans
cells treated with carvacrol demonstrated a bona fide UPR transcriptional signature. Ire1 activity detected by the splicing of
HAC1
mRNA in
C. albicans
was activated by carvacrol. Furthermore, carvacrol was found to potentiate antifungal activity of the echinocandin antifungal caspofungin and UPR inducers dithiothreitol and tunicamycin against
C. albicans
. This comprehensive chemogenomic investigation demonstrated that carvacrol exerts its antifungal activity by altering ER integrity, leading to ER stress and the activation of the UPR to restore protein-folding homeostasis.
Dissemination of IncI2 Plasmids That Harbor the
bla
CTX-M
Element among Clinical Salmonella Isolates
Authors: Wong Marcus Ho-yin , Liu Lizhang , Yan Meiying , Chan Edward Wai-chi , Chen Sheng 
Published: May 2015

ABSTRACT

The extended-spectrum-β-lactamase (ESBL) determinant CTX-M-55 is increasingly prevalent in
Escherichia coli
but remains extremely rare in
Salmonella
. This study reports the isolation of a plasmid harboring the
bla
CTX-M-55
element in a clinical
Salmonella enterica
serotype Typhimurium strain resistant to multiple antibiotics. This plasmid is genetically identical to several known IncI2-type elements harbored by
E. coli
strains recovered from animals. This finding indicates that IncI2 plasmids harboring the
bla
CTX-M
genes may undergo cross-species migration among potential bacterial pathogens, with
E. coli
as the major source of such elements.
Activity of Imipenem with Relebactam against Gram-Negative Pathogens from New York City
Authors: Lapuebla Amabel , Abdallah Marie , Olafisoye Olawole , Cortes Christopher , Urban Carl , Landman David , Quale John 
Published: May 2015

ABSTRACT

Imipenem with relebactam was active against
Escherichia coli
,
Klebsiella pneumoniae
, and
Enterobacter
spp., including
K. pneumoniae
carbapenemase (KPC)-producing isolates. Loss of OmpK36 in KPC-producing
K. pneumoniae
isolates affected the susceptibility of this combination. Enhanced activity was evident against
Pseudomonas aeruginosa
, including isolates with depressed
oprD
and increased
ampC
expression. However, the addition of relebactam to imipenem did not provide added benefit against
Acinetobacter baumannii
. The combination of imipenem with relebactam demonstrated activity against KPC-producing
Enterobacteriaceae
and multidrug-resistant
P. aeruginosa
.
Staphylococcus aureus Infections: Epidemiology, Pathophysiology, Clinical Manifestations, and Management
Authors: Tong Steven Y. C. , Davis Joshua S. , Eichenberger Emily , Holland Thomas L. , Fowler Vance G. 
Published: May 2015

SUMMARY

Staphylococcus aureus
is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of
S. aureus
infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.
Neutrophils Play an Important Role in Protective Immunity against Coxiella burnetii Infection
Authors: Elliott Alexandra , Schoenlaub Laura , Freches Danielle , Mitchell William , Zhang Guoquan 
Published: May 2015

ABSTRACT

Coxiella burnetii
is an obligate intracellular Gram-negative bacterium that causes the zoonotic disease Q fever. Although Q fever is mainly transmitted by aerosol infection, study of the immune responses in the lung following pulmonary
C. burnetii
infection is lacking. Neutrophils are considered the first immune cell to migrate into the lung and play an important role in host defense against aerosol infection with microbial pathogens. However, the role of neutrophils in the host defense against
C. burnetii
infection remains unclear. To determine the role of neutrophils in protective immunity against
C. burnetii
infection, the RB6-8C5 antibody was used to deplete neutrophils in mice before intranasal infection with
C. burnetii
. The results indicated that neutrophil-depleted mice developed more severe disease than their wild-type counterparts, suggesting that neutrophils play an important role in host defense against
C. burnetii
pulmonary infection. We also found that neither CXC chemokine receptor 2 (CXCR2) nor interleukin-17 (IL-17) receptor (IL-17R) deficiency changed the severity of disease following intranasal
C. burnetii
challenge, suggesting that keratinocyte-derived chemokine and IL-17 may not play essential roles in the response to
C. burnetii
infection. However, significantly higher
C. burnetii
genome copy numbers were detected in the lungs of IL-1R
−/−
mice at 14 days postinfection. This indicates that IL-1 may be important for the clearance of
C. burnetii
from the lungs following intranasal infection. Our results also suggest that neutrophils are involved in protecting vaccinated mice from
C. burnetii
challenge-induced disease. This is the first study to demonstrate an important role for neutrophils in protective immunity against
C. burnetii
infection.
Transcriptome Reprogramming by Plasmid-Encoded Transcriptional Regulators Is Required for Host Niche Adaption of a Macrophage Pathogen
Authors: Coulson Garry B. , Miranda-CasoLuengo Aleksandra A. , Miranda-CasoLuengo Raúl , Wang Xiaoguang , Oliver Jenna , Willingham-Lane Jennifer M. , Meijer Wim G. , Hondalus Mary K. 
Published: May 2015

ABSTRACT

Rhodococcus equi
is a facultative intracellular pathogen of macrophages, relying on the presence of a conjugative virulence plasmid harboring a 21-kb pathogenicity island (PAI) for growth in host macrophages. The PAI encodes a family of 6 virulence-associated proteins (Vaps) in addition to 20 other proteins. The contribution of these to virulence has remained unclear. We show that the presence of only 3 virulence plasmid genes (of 73 in total) is required and sufficient for intracellular growth. These include a single
vap
family member,
vapA
, and two PAI-located transcriptional regulators,
virR
and
virS
. Both transcriptional regulators are essential for wild-type-level expression of
vapA
, yet
vapA
expression alone is not sufficient to allow intracellular growth. A whole-genome microarray analysis revealed that VirR and VirS substantially integrate themselves into the chromosomal regulatory network, significantly altering the transcription of 18% of all chromosomal genes. This pathoadaptation involved significant enrichment of select gene ontologies, in particular, enrichment of genes involved in transport processes, energy production, and cellular metabolism, suggesting a major change in cell physiology allowing the bacterium to grow in the hostile environment of the host cell. The results suggest that following the acquisition of the virulence plasmid by an avirulent ancestor of
R. equi
, coevolution between the plasmid and the chromosome took place, allowing VirR and VirS to regulate the transcription of chromosomal genes in a process that ultimately promoted intracellular growth. Our findings suggest a mechanism for cooption of existing chromosomal traits during the evolution of a pathogenic bacterium from an avirulent saprophyte.
Intracellular Listeria monocytogenes Comprises a Minimal but Vital Fraction of the Intestinal Burden following Foodborne Infection
Authors: Jones Grant S. , Bussell Kate M. , Myers-Morales Tanya , Fieldhouse Abigail M. , Bou Ghanem Elsa N. , D'Orazio Sarah E. F. 
Published: May 2015

ABSTRACT

Listeria monocytogenes
is a highly adaptive bacterium that replicates as a free-living saprophyte in the environment as well as a facultative intracellular pathogen that causes invasive foodborne infections. The intracellular life cycle of
L. monocytogenes
is considered to be its primary virulence determinant during mammalian infection; however, the proportion of
L. monocytogenes
that is intracellular
in vivo
has not been studied extensively. In this report, we demonstrate that the majority of wild-type (strain EGDe) and mouse-adapted (InlA
m
-expressing)
L. monocytogenes
recovered from the mesenteric lymph nodes (MLN) was extracellular within the first few days after foodborne infection. In addition, significantly lower burdens of
L. monocytogenes
were recovered from the colon, spleen, and liver of gentamicin-treated mice than of control mice. This led us to investigate whether intracellular replication of
L. monocytogenes
was essential during the intestinal phase of infection. We found that lipoate protein ligase-deficient
L. monocytogenes
(Δ
lplA1
) mutants, which display impaired intracellular growth, were able to colonize the colon but did not persist efficiently and had a significant defect in spreading to the MLN, spleen, and liver. Together, these data indicate that the majority of the
L. monocytogenes
burden in the gastrointestinal tract is extracellular, but the small proportion of intracellular
L. monocytogenes
is essential for dissemination to the MLN and systemic organs.
Chlamydial Variants Differ in Ability To Ascend the Genital Tract in the Guinea Pig Model of Chlamydial Genital Infection
Authors: Yeruva Laxmi , Bowlin Anne K. , Spencer Nicole , Maurelli Anthony T. , Rank Roger G. 
Published: May 2015

ABSTRACT

An important question in the study of chlamydial genital tract disease is why some women develop severe upper tract disease while others have mild or even “silent” infections with or without pathology. Animal studies suggest that the pathological outcome of an infection is dependent upon both the composition of the infecting chlamydial population and the genotype of the host, along with host physiological effects, such as the cyclical production of reproductive hormones and even the size of the infecting inoculum or the number of repeated infections. In this study, we compared two variants of
Chlamydia caviae
, contrasting in virulence, with respect to their abilities to ascend the guinea pig genital tract. We then determined the effect of combining the two variants on the course of infection and on the bacterial loads of the two variants in the genital tract. Although the variants individually had similar infection kinetics in the cervix, SP6, the virulent variant, could be isolated from the oviducts more often and in greater numbers than the attenuated variant, AZ2. SP6 also elicited higher levels of interleukin 8 (IL-8) in the lower genital tract and increased leukocyte infiltration in the cervix and uterus compared to AZ2. When the two variants were combined in a mixed infection, SP6 outcompeted AZ2 in the lower genital tract; however, AZ2 was able to ascend the genital tract as readily as SP6. These data suggest that the ability of SP6 to elicit an inflammatory response in the lower genital tract facilitates the spread of both variants to the oviducts.
The Crystal Structure of Nitrosomonas europaea Sucrose Synthase Reveals Critical Conformational Changes and Insights into Sucrose Metabolism in Prokaryotes
Authors: Wu Rui , Asención Diez Matías D. , Figueroa Carlos M. , Machtey Matías , Iglesias Alberto A. , Ballicora Miguel A. , Liu Dali 
Published: May 2015

ABSTRACT

In this paper we report the first crystal structure of a prokaryotic sucrose synthase from the nonphotosynthetic bacterium
Nitrosomonas europaea
. The obtained structure was in an open form, whereas the only other available structure, from the plant
Arabidopsis thaliana
, was in a closed conformation. Comparative structural analysis revealed a “hinge-latch” combination, which is critical to transition between the open and closed forms of the enzyme. The
N. europaea
sucrose synthase shares the same fold as the GT-B family of the retaining glycosyltransferases. In addition, a triad of conserved homologous catalytic residues in the family was shown to be functionally critical in the
N. europaea
sucrose synthase (Arg567, Lys572, and Glu663). This implies that sucrose synthase shares not only a common origin with the GT-B family but also a similar catalytic mechanism. The enzyme preferred transferring glucose from ADP-glucose rather than UDP-glucose like the eukaryotic counterparts. This predicts that these prokaryotic organisms have a different sucrose metabolic scenario from plants. Nucleotide preference determines where the glucose moiety is targeted after sucrose is degraded.

IMPORTANCE
We obtained biochemical and structural evidence of sucrose metabolism in nonphotosynthetic bacteria. Until now, only sucrose synthases from photosynthetic organisms have been characterized. Here, we provide the crystal structure of the sucrose synthase from the chemolithoautotroph
N. europaea
. The structure supported that the enzyme functions with an open/close induced fit mechanism. The enzyme prefers as the substrate adenine-based nucleotides rather than uridine-based like the eukaryotic counterparts, implying a strong connection between sucrose and glycogen metabolism in these bacteria. Mutagenesis data showed that the catalytic mechanism must be conserved not only in sucrose synthases but also in all other retaining GT-B glycosyltransferases.
Phase-Variable Control of Multiple Phenotypes in Acinetobacter baumannii Strain AB5075
Authors: Tipton Kyle A. , Dimitrova Daniela , Rather Philip N. 
Published: May 2015

ABSTRACT

Acinetobacter baumannii
strain AB5075 produces colonies with two opacity phenotypes, designated opaque and translucent. These phenotypes were unstable and opaque and translucent colony variants were observed to interconvert at high frequency, suggesting that a phase-variable mechanism was responsible. The frequency of phase variation both within colonies and in broth cultures increased in a cell density-dependent manner and was mediated by the accumulation of an extracellular factor. This factor was distinct from the known
A. baumannii
signaling molecule 3-OH C
12
-homoserine lactone. Opaque and translucent colony variants exhibited a number of phenotypic differences, including cell morphology, surface motility, biofilm formation, antibiotic resistance, and virulence in a
Galleria mellonella
model. Additional clinical isolates exhibited a similar phase-variable control of colony opacity, suggesting that this may be a common feature of
A. baumannii
.

IMPORTANCE
A novel phase-variable mechanism has been identified in
Acinetobacter baumannii
that results in an interconversion between opaque and translucent colony phenotypes. This phase variation also coordinately regulates motility, cell shape, biofilm formation, antibiotic resistance, and virulence. The frequency of phase variation is increased at high cell density via a diffusible extracellular signal. To our knowledge, this report presents the first example of phase variation in
A. baumannii
and also the first example of quorum sensing-mediated control of phase variation in a bacterium. The findings are important, as this phase-variable mechanism can be identified only via changes in colony opacity using oblique light; therefore, many researchers studying
A. baumannii
may unknowingly be working with different colony variants.