bluuebunny/crossref_metadata_2025_split huggingface dataset:
Importance of Heat-Labile Enterotoxin in Colonization of the Adult Mouse Small Intestine by Human EnterotoxigenicEscherichia coliStrains
Authors: Allen Kenneth P. , Randolph Mildred M. , Fleckenstein James M. 
Published: January 2006

ABSTRACTEnterotoxigenicEscherichia coli(ETEC) infections are a significant cause of diarrheal disease and infant mortality in developing countries. Studies of ETEC pathogenesis relevant to vaccine development have been greatly hampered by the lack of a suitable small-animal model of infection with human ETEC strains. Here, we demonstrate that adult immunocompetent outbred mice can be effectively colonized with the prototypical human ETEC H10407 strain (colonization factor antigen I; heat-labile and heat-stable enterotoxin positive) and that production of heat-labile holotoxin provides a significant advantage in colonization of the small intestine in this model.
Sigma B Contributes toListeria monocytogenesGastrointestinal Infection but Not to Systemic Spread in the Guinea Pig Infection Model
Authors: Garner M. R. , Njaa B. L. , Wiedmann M. , Boor K. J. 
Published: January 2006

ABSTRACTContributions of the alternative sigma factor σBtoListeria monocytogenesinfection were investigated using strains bearing null mutations insigB,prfA, orinlAor in selectedinlAorprfApromoter regions. The ΔP4inlAstrain, which has a deletion in the σB-dependent P4inlApromoter, and the ΔsigBstrain had significantly reduced invasion efficiencies relative to that of the wild-type strain in the Caco-2 human colorectal epithelial cell line, while the invasion efficiency of a strain bearing a deletion in the partially σBdependent P2prfApromoter region did not differ from that of the wild type. The virulence of the ΔsigBand ΔP4inlAstrains was attenuated in intragastrically inoculated guinea pigs, with the ΔsigBstrain showing greater attenuation, while the virulence capacity of the ΔP2prfAstrain was similar to that of the wild-type strain, suggesting that attenuation of virulence due to the ΔsigBmutation does not result from loss of σB-dependentprfAtranscription. Our results show that σB-dependent activation ofinlAis important for cell invasion and gastrointestinal infection and suggest that σB-regulated genes in addition toinlAappear to contribute to gastrointestinal infection. Interestingly, the virulence of the ΔsigBstrain was not attenuated in intravenously infected guinea pigs. We conclude that (i)L. monocytogenesσBplays a critical role in invasion of human host cells, (ii) σB-mediated contributions to invasion are, in part, due to direct effects oninlAtranscription but not onprfAtranscription, and (iii) σBplays a critical role during the gastrointestinal stage of listeriosis in the guinea pig but is not important for systemic spread of the organism.
Phenotypic Switching in a
Cryptococcus neoformans
Variety
gattii
Strain Is Associated with Changes in Virulence and Promotes Dissemination to the Central Nervous System
Authors: Jain N. , Li Li , McFadden D. C. , Banarjee U. , Wang X. , Cook E. , Fries B. C. 
Published: January 2006

ABSTRACT

This is the first report of a
Cryptococcus neoformans
var.
gattii
strain (serotype B) that switches reversibly between its parent mucoid (NP1-MC) colony morphology and a smooth (NP1-SM) colony morphology. Similar to
C. neoformans
var.
grubii
and
C. neoformans
var.
neoformans
strains, the switch is associated with changes in the polysaccharide capsule and virulence in animal models. In murine infection models, NP1-MC is significantly more virulent than NP1-SM (
P
< 0.021). In contrast to the serotype A and D strains, the serotype B strain switches in vivo reversibly between both colony morphologies. The polysaccharide of NP1-MC exhibits a thicker capsule, and thus NP1-MC exhibits enhanced intracellular survival in macrophages. Consistent with this finding, switching to the mucoid variant is observed in pulmonary infection with NP1-SM. In contrast, the thin polysaccharide capsule of NP1-SM permits better crossing of the blood-brain barrier. In this regard, only smooth colonies were grown from brain homogenates of NP1-MC-infected mice. Our findings have important implications for the pathogenesis of cryptococcosis and suggest that phenotypic switching affects host-pathogen interactions in the local microenvironment. This altered interaction then selects for specific colony variants to arise in a pathogen population.
Entamoeba histolyticaInfection in Children and Protection from Subsequent Amebiasis
Authors: Haque Rashidul , Mondal Dinesh , Duggal Priya , Kabir Mamun , Roy Shantanu , Farr Barry M. , Sack R. Bradley , Petri William A. 
Published: January 2006

ABSTRACTThe contribution of amebiasis to the burden of diarrheal disease in children and the degree to which immunity is acquired from natural infection were assessed in a 4-year prospective observational study of 289 preschool children in an urban slum in Dhaka, Bangladesh.Entamoeba histolyticainfection was detected at least once in 80%, and repeat infection in 53%, of the children who completed 4 years of observation. Annually there were 0.09 episodes/child ofE. histolytica-associated diarrhea and 0.03 episodes/child ofE. histolytica-associated dysentery. Fecal immunoglobulin A (IgA) anti-parasite Gal/GalNAc lectin carbohydrate recognition domain (anti-CRD) was detected in 91% (183/202) of the children at least once and was associated with a lower incidence of infection and disease. We concluded that amebiasis was a substantial burden on the overall health of the cohort children. Protection from amebiasis was associated with a stool anti-CRD IgA response. The challenge of producing an effective vaccine will be to improve upon naturally acquired immunity, which does not provide absolute protection from reinfection.
N
-Acylhomoserine Lactones Antagonize Virulence Gene Expression and Quorum Sensing in
Staphylococcus aureus
Authors: Qazi Saara , Middleton Barry , Muharram Siti Hanna , Cockayne Alan , Hill Philip , O'Shea Paul , Chhabra Siri Ram , Cámara Miguel , Williams Paul 
Published: January 2006

ABSTRACT

Many gram-negative bacteria employ
N
-acylhomoserine lactone
(AHL)-mediated quorum sensing to control virulence. To determine
whether gram-positive bacteria such as
Staphylococcus aureus
respond to AHLs, we used a growth-dependent
lux
reporter
fusion. Exposure of
S. aureus
to different AHLs revealed that
3-oxo-substituted AHLs with C
10
to C
14
acyl
chains inhibited light output and growth in a concentration-dependent
manner, while short-chain AHLs had no effect.
N
-(3-Oxododecanoyl)-
l
-homoserine lactone
(3-oxo-C
12
-HSL) inhibited the production of exotoxins and
cell wall fibronectin-binding proteins but enhanced protein A
expression. Since these processes are reciprocally regulated via the
S. aureus agr
quorum-sensing system, which in turn, is
regulated via
sar
, we examined the effect of AHLs on
sarA
and
agr
. At sub-growth-inhibitory concentrations
of 3-oxo-C
12
-HSL, both
sarA
expression and
agr
expression were inhibited, indicating that the action of
3-oxo-C
12
-HSL is mediated at least in part through
antagonism of quorum sensing in
S. aureus
. Spent culture
supernatants from
Pseudomonas aeruginosa
, which produces both
3-oxo-C
12
-HSL and
N
-butanoyl-homoserine lactone
(C
4
-HSL), also inhibited
agr
expression, although
C
4
-HSL itself was inactive in this assay. Since quorum
sensing in
S. aureus
depends on the activities of
membrane-associated proteins, such as AgrB, AgrC, and AgrD, we
investigated whether AHLs perturbed
S. aureus
membrane
functionality by determining their influence on the membrane dipole
potential. From the binding curves obtained, a dissociation constant of
7 μM was obtained for 3-oxo-C
12
-HSL, indicating the
presence of a specific saturable receptor, whereas no binding was
observed for C
4
-HSL. These data demonstrate that long-chain
3-oxo-substituted AHLs, such as 3-oxo-C
12
-HSL, are capable
of interacting with the
S. aureus
cytoplasmic membrane in a
saturable, specific manner and at sub-growth-inhibitory concentrations,
down-regulating exotoxin production and both
sarA
and
agr
expression.
HpaA Is Essential forHelicobacter pyloriColonization in Mice
Authors: Carlsohn Elisabet , Nyström Johanna , Bölin Ingrid , Nilsson Carol L. , Svennerholm Ann-Mari 
Published: January 2006

ABSTRACTInfection with the human gastric pathogenHelicobacter pylorican give rise to chronic gastritis, peptic ulcer, and gastric cancer. AllH. pyloristrains express the surface-localized protein HpaA, a promising candidate for a vaccine againstH. pyloriinfection. To study the physiological importance of HpaA, a mutation of thehpaAgene was introduced into a mouse-adaptedH. pyloristrain. To justify that the interruption of thehpaAgene did not cause any polar effects of downstream genes or was associated with a second site mutation, the protein expression patterns of the mutant and wild-type strains were characterized by two different proteomic approaches. Two-dimensional differential in-gel electrophoresis analysis of whole-cell extracts and subcellular fractionation combined with nano-liquid chromatography-Fourier transform ion cyclotron resonance mass spectrometry for outer membrane protein profiling revealed only minor differences in the protein profile between the mutant and the wild-type strains. Therefore, the mutant strain was tested for its colonizing ability in a well-established mouse model. While inoculation with the wild-type strain resulted in heavilyH. pylori-infected mice, the HpaA mutant strain was not able to establish colonization. Thus, by combining proteomic analysis and in vivo studies, we conclude that HpaA is essential for the colonization ofH. pyloriin mice.
Activation of the
Vibrio cholerae
SOS Response Is Not Required for Intestinal Cholera Toxin Production or Colonization
Authors: Quinones Mariam , Davis Brigid M. , Waldor Matthew K. 
Published: January 2006

ABSTRACT

Cholera toxin, one of the main virulence factors of
Vibrio cholerae
, is encoded in the genome of CTXφ, a
V. cholerae
-specific lysogenic filamentous bacteriophage. Although the genes encoding cholera toxin,
ctxAB
, are known to have their own promoter, the toxin genes can also be transcribed from an upstream CTXφ promoter,

P
rstA

. The
V. cholerae
SOS response to DNA damage induces the CTX prophage by stimulating gene expression initiating from

P
rstA

. Here, we investigated whether
ctxA
mRNA levels increase along with the levels of the transcripts for the other CTXφ genes following stimulation of the
V. cholerae
SOS response. Treatment of
V. cholerae
with the SOS-inducing agent mitomycin C increased the level of
ctxA
mRNA approximately sevenfold, apparently by augmenting the activity of

P
rstA

. However, using suckling mice as a model host, we found that intraintestinal
ctxA
transcription does not depend on

P
rstA

. In fact, the suckling mouse intestine does not appear to be a potent inducer of the
V. cholerae
SOS response. Furthermore, alleviation of LexA-mediated repression of the
V. cholerae
SOS regulon was not required for
V. cholerae
growth in the suckling mouse intestine. Our observations suggest that pathogenicity of
V. cholerae
does not depend on its SOS response.
Identification of a Virulence-Associated Determinant, Dihydrolipoamide Dehydrogenase (
lpd
), in
Mycoplasma gallisepticum
through In Vivo Screening of Transposon Mutants
Authors: Hudson P. , Gorton T. S. , Papazisi L. , Cecchini K. , Frasca S. , Geary S. J. 
Published: January 2006

ABSTRACT

To effectively analyze
Mycoplasma gallisepticum
for virulence-associated determinants, the ability to create stable genetic mutations is essential. Global
M. gallisepticum
mutagenesis is currently limited to the use of transposons. Using the gram-positive transposon Tn
4001
mod, a mutant library of 110 transformants was constructed and all insertion sites were mapped. To identify transposon insertion points, a unique primer directed outward from the end of Tn
4001
mod was used to sequence flanking genomic regions. By comparing sequences obtained in this manner to the annotated
M. gallisepticum
genome, the precise locations of transposon insertions were discerned. After determining the transposon insertion site for each mutant, unique reverse primers were synthesized based on the specific sequences, and PCR was performed. The resultant amplicons were used as unique Tn
4001
mod mutant identifiers. This procedure is referred to as signature sequence mutagenesis (SSM). SSM permits the comprehensive screening of the
M. gallisepticum
genome for the identification of novel virulence-associated determinants from a mixed mutant population. To this end, chickens were challenged with a pool of 27 unique Tn
4001
mod mutants. Two weeks postinfection, the birds were sacrificed, and organisms were recovered from respiratory tract tissues and screened for the presence or absence of various mutants. SSM is a negative-selection screening technique whereby those mutants possessing transposon insertions in genes essential for in vivo survival are not recovered from the host. We have identified a virulence-associated gene encoding dihydrolipoamide dehydrogenase (
lpd
). A transposon insertion in the middle of the coding sequence resulted in diminished biologic function and reduced virulence of the mutant designated Mg 7.
Activation of Toll-Like Receptor 9 by DNA from Different Bacterial Species
Authors: Dalpke Alexander , Frank Jutta , Peter Mirjam , Heeg Klaus 
Published: January 2006

ABSTRACTToll-like receptor 9 (TLR-9) recognizes unmethylated CpG dinucleotides which are abundant in prokaryotic DNA and yet are rare in eukaryotic DNA. Little is known about the significance of TLR-9 in terms of recognition of different bacterial DNA species. In this study HEK293 cells stably transfected with human TLR-9 were used to analyze the immunostimulatory properties of 15 bacterial DNA preparations. In addition, bacterial genome data were analyzed for the frequency of unmethylated cytosine-guanosine ([CG]) dinucleotides. We observed that DNA samples of different bacteria showed considerable differences in their potential to stimulate TLR-9. This correlated with the frequency of [CG] dinucleotides. Based upon data from our experiments the estimate of immunostimulatory bacterial DNA concentrations translated to as high as 109bacteria/ml. Application of the transfection reagent DOTAP resulted in a more efficient delivery of DNA into the cell, and this went along with increased TLR-9 activation. The data indicate that bacterial DNA preparations from different species differ in their capacity to activate TLR-9, which is dependent on the individual [CG] content. Moreover, increased intracellular delivery results in a marked enhancement of immunostimulation.
Interleukin 1α Increases the Susceptibility of Rabbits to Experimental Viridans Streptococcal Endocarditis
Authors: Dankert Jacob , van der Werff Janneke , Joldersma Willem , Zaat Sebastian A. J. 
Published: January 2006

ABSTRACT

Major predisposing conditions for infective endocarditis (IE) are the presence of a cardiac platelet-fibrin vegetation and of circulating bacteria with relatively low susceptibility to microbicidal activity of blood platelets. The influence of proinflammatory conditions on development of IE is unknown. We studied the effects of the presence of a catheter, inserted to induce platelet-fibrin vegetations, and of the proinflammatory cytokine interleukin-1α in rabbit experimental IE. Leaving the catheter in place after challenge with viridans streptococci predisposed for experimental IE. IE susceptibility rapidly decreased between 0 to 6 h after catheter removal. The catheter did not predispose for IE by providing a site for bacterial adherence, as almost all explanted catheters were culture negative. To mimic the proinflammatory influence of the catheter, rabbits were injected with interleukin-1α at 24 h after catheter removal and at 0, 1, and 3 h before bacterial challenge. Interleukin-1α injected 3 h prior to challenge significantly increased IE incidence due to a platelet releasate-susceptible
Streptococcus oralis
strain, with rapidly increasing numbers of bacteria within the vegetations. IE due to the
Streptococcus sanguis
strain less susceptible to platelet releasate was not enhanced. We conclude that proinflammatory stimuli, either a catheter or interleukin-1α, enhanced susceptibility to IE due to the platelet releasate-susceptible
S. oralis
. As with rabbits, temporary intravascular proinflammatory conditions may predispose for IE in humans at risk for this serious infection.
Ancylostoma caninum
MTP-1, an Astacin-Like Metalloprotease Secreted by Infective Hookworm Larvae, Is Involved in Tissue Migration
Authors: Williamson Angela L. , Lustigman Sara , Oksov Yelena , Deumic Vehid , Plieskatt Jordan , Mendez Susana , Zhan Bin , Bottazzi Maria Elena , Hotez Peter J. , Loukas Alex 
Published: January 2006

ABSTRACT

Infective larvae (L3) of nematodes secrete macromolecules that are critical to infection and establishment of the parasite in the host. The dog hookworm
Ancylostoma caninum
secretes an astacin-like metalloprotease,
Ac
-MTP-1, upon activation in vitro with host serum. Recombinant
Ac
-MTP-1 was expressed in the baculovirus/insect cell system as a secreted protein and was purified from culture medium by two separate methods, cation-exchange fast-performance liquid chromatography and gelatin-affinity chromatography. Recombinant MTP-1 was catalytically active and digested a range of native and denatured connective tissue substrates, including gelatin, collagen, laminin, and fibronectin. A dog was immunized with recombinant
Ac
-MTP-1 formulated with AS03 adjuvant, and the antiserum was used to immunolocalize the anatomic sites of expression within
A. caninum
L3 to secretory granules in the glandular esophagus and the channels that connect the esophagus to the L3 surface and to the cuticle. Antiserum inhibited the ability of recombinant MTP-1 to digest collagen by 85% and inhibited larval migration through tissue in vitro by 70 to 75%, in contrast to just 5 to 10% inhibition obtained with preimmunization serum. The metalloprotease inhibitors EDTA and 1,10-phenanthroline also reduced the penetration of L3 through skin in vitro by 43 to 61%. The data strongly suggest that
Ac
-MTP-1 is critical for the invasion process of hookworm larvae, and moreover, that antibodies against the enzyme can neutralize its function and inhibit migration.
Safety and Immunogenicity of an Oral Inactivated Whole-CellPseudomonas aeruginosaVaccine Administered to Healthy Human Subjects
Authors: Cripps Allan W. , Peek Keith , Dunkley Margaret , Vento Kevin , Marjason Joanne K. , McIntyre Madonna E. , Sizer Phil , Croft Duncan , Sedlak-Weinstein Lis 
Published: January 2006

ABSTRACTThis study examines the safety and immunogenicity of an oral, whole-cellPseudomonas aeruginosavaccine administered to healthy volunteers. Thirty subjects received an oral dose of Pseudostat in two timed, measured doses with serological follow-up to 56 days postvaccination. Following vaccination, several individuals were identified as antibody responders for all three immunoglobulin (Ig) isotypes tested, specifically against whole-cellP. aeruginosaextract and outer membrane proteins F and I. The mean pooled lipopolysaccharide antigen-specific IgA showed the most significant and constant increases in titer postdose, with a similar increase in titer for whole-cellP. aeruginosaextract-specific IgA. The results demonstrated an increased phagocytic ability of the selected macrophage cell line in post vaccination sera. Furthermore a significant increase in intracellular macrophage killing of opsonizedP. aeruginosawas also demonstrated (82% on day 14 postdose) in the presence of the postvaccination sera. The safety component of the study did not show any vaccine-attributable adverse effects in any of the subjects, as documented by clinical evidence, hematology, and biochemistry profiles. We conclude that Pseudostat is safe and immunogenic in humans at this dose and that further studies to determine the appropriate dosage and efficacy are needed. In our study, we have shown that the most significant and sustained responses to oral vaccination in human adult volunteers were serum IgA levels and that pooled sera collected postimmunization have an increased capacity to promote opsonophagocytotic killing ofP. aeruginosa.
A Live-Attenuated
Pseudomonas aeruginosa
Vaccine Elicits Outer Membrane Protein-Specific Active and Passive Protection against Corneal Infection
Authors: Zaidi Tanweer S. , Priebe Gregory P. , Pier Gerald B. 
Published: January 2006

ABSTRACT

Pseudomonas aeruginosa
can cause sight-threatening corneal infections in humans, particularly those who wear contact lenses. We have previously shown that a live-attenuated
P. aeruginosa
vaccine given intranasally protected mice against acute lethal pneumonia in a lipopolysaccharide (LPS) serogroup-specific manner. In the current study, we evaluated the protective and therapeutic efficacies, as well as the target antigens, of this vaccine in a murine corneal infection model. C3H/HeN mice were nasally immunized with the vaccine (an
aroA
deletion mutant of strain PAO1, designated PAO1Δ
aroA
) or with
Escherichia coli
as a control and were challenged 3 weeks later by inoculating the scratch-injured cornea with
P. aeruginosa
. For passive prophylaxis and therapy, we utilized a serum raised in rabbits nasally immunized with PAO1Δ
aroA
or
E. coli
. Outcome measures included corneal pathology scores and, in some experiments, reductions in total and internalized bacterial CFU. We found that both active and passive immunization reduced corneal pathology scores after challenge with a variety of
P. aeruginosa
strains, including several serogroup-heterologous strains. Even when given therapeutically starting as late as 24 h after infection, the rabbit antiserum to PAO1Δ
aroA
was effective at reducing corneal pathology scores. Immunotherapy of established infections also reduced the numbers of total and internalized corneal
P. aeruginosa
bacteria. Experiments using absorbed sera showed that the protective antibodies are specific to outer membrane proteins. Thus, live-attenuated
P. aeruginosa
vaccines delivered nasally protect against corneal infections in mice and potentially can be used to prepare passive therapy reagents for the treatment of established
P. aeruginosa
corneal infections caused by diverse LPS serogroups.