bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bordetella avium
Virulence Measured In Vivo and In Vitro
Authors: Temple Louise M. , Weiss Alison A. , Walker Kimberly E. , Barnes H. John , Christensen Vern L. , Miyamoto David M. , Shelton Celia B. , Orndorff Paul E. 
Published: December 2019

ABSTRACT

Bordetella avium
causes an upper-respiratory-tract disease called bordetellosis in birds. Bordetellosis shares many of the clinical and histopathological features of disease caused in mammals by
Bordetella pertussis
and
Bordetella bronchiseptica
. In this study we determined several parameters of infection in the domestic turkey,
Meleagris galapavo
, and compared these in vivo findings with an in vitro measure of adherence using turkey tracheal rings. In the in vivo experiments, we determined the effects of age, group size, infection duration, and interindividual spread of
B. avium
. Also, the effect of host genetic background on susceptibility was tested in the five major commercial turkey lines by infecting each with the parental
B. avium
strain and three
B. avium
insertion mutants. The mutant strains lacked either motility, the ability to agglutinate guinea pig erythrocytes, or the ability to produce dermonecrotic toxin. The susceptibilities of 1-day-old and 1-week-old turkeys to
B. avium
were the same, and challenge group size (5, 8, or 10 birds) had no effect upon the 50% infectious dose. Two weeks between inoculation and tracheal culture was optimal, since an avirulent mutant (unable to produce dermonecrotic toxin) persisted for a shorter time. Communicability of the
B. avium
parental strain between confined birds was modest, but a nonmotile mutant was less able to spread between birds. There were no host-associated differences in susceptibility to the parental strain and the three
B. avium
mutant strains just mentioned: in all turkey lines tested, the dermonecrotic toxin- and hemagglutination-negative mutants were avirulent whereas the nonmotile mutants showed no loss of virulence. Interestingly, the ability of a strain to cause disease in vivo correlated completely with its ability to adhere to ciliated tracheal cells in vitro.
Interaction ofListeria monocytogeneswith Human Brain Microvascular Endothelial Cells: InlB-Dependent Invasion, Long-Term Intracellular Growth, and Spread from Macrophages to Endothelial Cells
Authors: Greiffenberg Lars , Goebel Werner , Kim Kwang Sik , Weiglein Inge , Bubert Andreas , Engelbrecht Fredi , Stins Monique , Kuhn Michael 
Published: December 2019

ABSTRACTInvasion of endothelial tissues may be crucial in aListeria monocytogenesinfection leading to meningitis and/or encephalitis. Internalization ofL. monocytogenesinto endothelial cells has been previously demonstrated by using human umbilical vein endothelial cells as a model system. However, during the crossing of the blood-brain barrier,L. monocytogenesmost likely encounters brain microvascular endothelial cells which are strikingly different from macrovascular or umbilical vein endothelial cells. In the present study human brain microvascular endothelial cells (HBMEC) were used to study the interaction ofL. monocytogeneswith endothelial cells, which closely resemble native microvascular endothelial cells of the brain. We show thatL. monocytogenesinvades HBMEC in an InlB-dependent and wortmannin-insensitive manner. Once within the HBMEC,L. monocytogenesreplicates efficiently over a period of at least 18 h, moves intracellularly by inducing actin tail formation, and spreads from cell to cell. Using a green fluorescent protein-expressingL. monocytogenesstrain, we present direct evidence that HBMEC are highly resistant to damage by intracellularly growingL. monocytogenes. Infection of HBMEC withL. monocytogenesresults in foci of heavily infected, but largely undamaged endothelial cells. Heterologous plaque assays withL. monocytogenes-infected P388D1macrophages as vectors demonstrate efficient spreading ofL. monocytogenesinto HBMEC, fibroblasts, hepatocytes, and epithelial cells, and this phenomenon is independent of theinlCgene product.
Inhibition ofSalmonella typhimuriumInvasion by Host Cell Expression of Secreted Bacterial Invasion Proteins
Authors: Carlson Steve A. , Jones Bradley D. 
Published: December 2019

ABSTRACTPathogenicSalmonellaspecies initiate infection of a host by inducing their own uptake into intestinal epithelial cells. An invasive phenotype is conferred to this pathogen by a number of proteins that are components of a type III secretion system. During the invasion process, the bacteria utilize this secretion system to release proteins that enter the host cell and apparently interact with unknown host cell components that induce alterations in the actin cytoskeleton. To investigate the role of secreted proteins as direct modulators of invasion, we have evaluated the ability ofSalmonella typhimuriumto enter mammalian cells that express portions of theSalmonellainvasion proteins SipB and SipC. Plasma membrane localization of SipB and SipC was achieved by fusing carboxyl- and amino-terminal portions of each invasion protein to the intracellular carboxyl-terminal tail of a membrane-bound eukaryotic receptor. Expression of receptor chimeras possessing the carboxyl terminus of SipB or the amino terminus of SipC blockedSalmonellainvasion, whereas expression of their chimeric counterparts had no effect on invasion. The effect on invasion was specific forSalmonellasince the perturbation of uptake was not extended to other invasive bacterial species. These results suggest thatSalmonellainvasion can be competitively inhibited by preventing the intracellular effects of SipB or SipC. In addition, these experiments provide a model for examining interactions between bacterial invasion proteins and their host cell targets.
CD4+T-Lymphocyte and Immunoglobulin G2 Responses in Calves Immunized withAnaplasma marginaleOuter Membranes and Protected against Homologous Challenge
Authors: Brown Wendy C. , Shkap Varda , Zhu Daming , McGuire Travis C. , Tuo Wenbin , McElwain Terry F. , Palmer Guy H. 
Published: December 2019

ABSTRACTProtective immunity against the ehrlichial pathogenAnaplasma marginalehas been hypothesized to require induction of immunoglobulin G2 (IgG2) antibody against outer membrane protein epitopes and coordinated activation of macrophages for phagocytosis and killing. In the present study, cell-mediated immune responses, including induction of IgG isotype switching, were characterized in calves immunized with purified outer membranes of the Florida strain ofA. marginale. Importantly, these calves were subsequently shown to be protected upon experimental challenge with the Florida strain, and calves which developed the highest IgG2 titers were completely protected against infection. Peripheral blood mononuclear cells (PBMC) obtained after immunization proliferated strongly in response to both wholeA. marginalehomogenates and purified outer membranes, and this responsiveness persisted until the time of challenge. Responding cells were shown to be CD4+T cells, and CD4+T-cell lines cultured for 2 to 4 weeks also proliferated specifically in response toA. marginaleand produced high titers of gamma interferon. The helper T-cell response included recognition of conserved epitopes, as PBMC proliferation was stimulated by the homologous Florida strain, four genetically distinctA. marginalestrains, andAnaplasma ovis. The outer membrane proteins stimulating the PBMC responses in protected calves included major surface proteins (MSPs) MSP-1, MSP-2, and MSP-3, which were previously shown to induce partial protection against infection. These studies demonstrate, for the first time, potent helper T-cell responses in cattle protectively immunized with outer membranes againstA. marginalechallenge and identify three MSPs that are recognized by immune T cells. These experiments provide the basis for subsequent identification of the helper T-cell epitopes on MSP-1, MSP-2, and MSP-3 that are needed to evoke anamnestic antibody and effector T-cell responses elicited by protein or nucleic acid immunization.
High-Level Expression ofChlamydia psittaciMajor Outer Membrane Protein in COS Cells and in Skeletal Muscles of Turkeys
Authors: Vanrompay D. , Cox E. , Mast J. , Goddeeris B. , Volckaert G. 
Published: December 2019

ABSTRACTTheomp1genes encoding the major outer membrane proteins (MOMPs) of avianChlamydia psittaciserovar A and D strains were cloned and sequenced. The nucleotide sequences of the avianC. psittaciserovar A and D MOMP genes were found to be 98.9 and 87.8% identical, respectively, to that of the avianC. psittaciserovar A strain 6BC, 84.6 and 99.8% identical to that of the avianC. psittaciserovar D strain NJ1, 79.1 and 81.1% identical to that of theC. psittaciguinea pig inclusion conjunctivitis strain, 60.9 and 62.5% identical to that of theChlamydia trachomatisL2 strain, and 57.5 and 60.4% identical to that of theChlamydia pneumoniaeIOL-207 strain. The serovar A or D MOMPs were cloned in the mammalian expression plasmid pcDNA1. When pcDNA1/MOMP A or pcDNA1/MOMP D was introduced into COS7 cells, a 40-kDa protein that was identical in size, antigenicity, and electrophoretic mobility to native MOMP was produced. Recombinant MOMP (rMOMP) was located in the cytoplasm of transfected COS7 cells as well as in the plasma membrane and was immunoaccessible. Intramuscular administration of pcDNA1/MOMP in specific-pathogen-free turkeys resulted in local expression of rMOMP in its native conformation, after which anti-MOMP antibodies appeared in the serum.
Murine Model of
Bartonella henselae
Infection in the Immunocompetent Host
Authors: Regnath T. , Mielke M. E. A. , Arvand M. , Hahn H. 
Published: December 2019

ABSTRACT

Bartonella henselae
is an emerging pathogen causing cat scratch disease, bacillary angiomatosis, and peliosis hepatis. Progress in understanding the pathogenesis of and the immune response to these infections has been limited by the lack of an animal model. Following intraperitoneal infection of C57BL/6 mice with
B. henselae
, organs were cleared of cultivatable bacteria within 6 days. In contrast,
B. henselae
DNA could be detected in liver tissue for at least 3 months. Liver tissue showed granulomatous inflammation reaching its highest degree of intensity during the fourth week of infection and resolving within 12 weeks postinfection. This mouse model is applicable to the study of the pathogenesis of
B. henselae
and the immune response to this pathogen in the immunocompetent host.
Molecular and Functional Characterization of
Salmonella enterica
Serovar Typhimurium
poxA
Gene: Effect on Attenuation of Virulence and Protection
Authors: Kaniga Koné , Compton Melissa S. , Curtiss Roy , Sundaram Preeti 
Published: December 2019

ABSTRACT

Salmonella enterica poxA
mutants exhibit a pleiotropic phenotype, including reduced pyruvate oxidase activity; reduced growth rate; and hypersensitivity to the herbicide sulfometuron methyl, α-ketobutyrate, and amino acid analogs. These mutants also failed to grow in the presence of the host antimicrobial peptide, protamine. In this study, PoxA
−
mutants of
S. enterica
serovar Typhimurium (
S. typhimurium
) were found to be 10,000-fold attenuated in orally inoculated BALB/c mice and 1,000-fold attenuated in intraperitoneally inoculated BALB/c mice, compared to wild-type
S. typhimurium
UK-1. In addition,
poxA
mutants were found to be capable of colonizing the spleen, mesenteric lymph nodes, and Peyer’s patches; to induce strong humoral immune responses; and to protect mice against a lethal wild-type
Salmonella
challenge. A 2-kb DNA fragment was isolated from wild-type
S. typhimurium
UK-1 based on its ability to complement an isogenic
poxA
mutant. The nucleotide sequence of this DNA fragment revealed an open reading frame of 325 amino acids capable of encoding a polypeptide of 36.8 kDa that was confirmed in the bacteriophage T7 expression system. Comparison of the translated sequence to the available databases indicated high homology to a family of lysyl-tRNA synthetases. Our results indicate that a mutation of
poxA
has an attenuating effect on
Salmonella
virulence. Further,
poxA
mutants are immunogenic and could be useful in designing live vaccines with a variety of bacterial species. To our knowledge, this is the first report on the effect of
poxA
mutation on bacterial virulence.
Activity of the Mitogenic
Pasteurella multocida
Toxin Requires an Essential C-Terminal Residue
Authors: Ward Philip N. , Miles Antony J. , Sumner Ian G. , Thomas Lewis H. , Lax Alistair J. 
Published: December 2019

ABSTRACT

Pasteurella multocida
toxin (PMT) is a potent mitogen that also affects bone resorption. PMT acts intracellularly and is therefore postulated to have several domains involved in different aspects of its function. The toxin contains eight cysteine residues. Mutants with individual substitutions for each of these residues were constructed, and the effects of these on the biological activity of the toxin were determined by cultured-cell assays. Only the most C-terminal of the eight cysteines (C1165) was essential for full activity, although mutation of the cysteine residue at position 1159 caused a slight but reproducible loss of potency. In animal challenge experiments, mutant toxin (C1165S) was not toxic to piglets, even at doses exceeding a lethal dose of active PMT 1,000-fold. The mutant and wild-type toxins displayed identical purification characteristics, similar susceptibility to proteolytic digestion, and circular dichroism profiles, which indicated that no gross structural changes had taken place. The function of the essential C1165 residue is not yet known, although its most likely role is an enzymatic one at or near the catalytic center of the toxin.
TetR Is a Positive Regulator of the Tetanus Toxin Gene in
Clostridium tetani
and Is Homologous to BotR
Authors: Marvaud Jean-Christophe , Eisel Ulrich , Binz Thomas , Niemann Heiner , Popoff Michel R. 
Published: December 2019

ABSTRACT

The TetR gene immediately upstream from the tetanus toxin (TeTx) gene was characterized. It encodes a 21,562-Da protein which is related (50 to 65% identity) to the equivalent genes (
botR
) in
Clostridium botulinum
. TetR has the feature of a DNA binding protein with a basic pI (9.53). It contains a helix-turn-helix motif and shows 29% identity with other putative regulatory genes in
Clostridium
, i.e.,
uviA
from
C. perfringens
and
txeR
from
C. difficile
. We report for the first time the transformation of
C. tetani
by electroporation, which permitted us to investigate the function of
tetR
. Overexpression of
tetR
in
C. tetani
induced an increase in TeTx production and in the level of the corresponding mRNA. This indicates that TetR is a transcriptional activator of the TeTx gene. Overexpression of
botR/A
(60% identity with TetR at the amino acid level) in
C. tetani
induced an increase in TeTx production comparable to that for overexpression of
tetR
. However,
botR/C
(50% identity with TetR at the amino acid level) was less efficient. This supports that TetR positively regulates the TeTx gene in
C. tetani
and that a conserved mechanism of regulation of the neurotoxin genes is involved in
C. tetani
and
C. botulinum
.
Identification and Characterization of a Phase-Variable NonfimbrialSalmonella typhimuriumGene That Alters O-Antigen Production
Authors: Kwan Lola Y. , Isaacson Richard E. 
Published: December 2019

ABSTRACTSalmonella typhimurium798, which was isolated from a pig, is known to phase vary from a nonadhesive to an adhesive phenotype. Cells of the adhesive phenotype adhere to porcine enterocytes, are more readily phagocytized by porcine neutrophils and macrophages, and once phagocytized can survive intracellularly, while cells of the nonadhesive phenotype die rapidly. The effect of phenotypic switching also can be visualized by changes in colony morphologies and the presence of between 10 and 15 proteins in the envelopes of cells in the adhesive phenotype. Mutants previously constructed with cells in the adhesive phenotype and the transposon TnphoAwere screened to identify mutants lacking one or more of the unique proteins. One mutation was cloned and sequenced, and the mutation was shown to be inrfaL(O-antigen ligase). Expression of O antigen was shown to be phase variable. The adhesive strain expressed an O antigen that was at least eightfold longer than that for the nonadhesive strain and by virtue of O-antigen production was resistant to porcine complement. The mutant survived intracellularly in phagocytic cells as well as its wild-type parent.
A Vaccine and Monoclonal Antibodies That Enhance Mouse Resistance toCandida albicansVaginal Infection
Authors: Han Yongmoon , Morrison Richard P. , Cutler Jim E. 
Published: December 2019

ABSTRACTWe previously reported that a vaccine composed of liposome-mannan complexes ofCandida albicans(L-mann) stimulates mice to produce protective antibodies against disseminated candidiasis. An immunoglobulin M (IgM) monoclonal antibody (MAb), B6.1, specific for a β-1,2-mannotriose in the complexes protects against the disease, whereas MAb B6 does not. In the present study, the vaccine and MAbs B6.1 and B6 were tested for the ability to protect againstCandidavaginal infection, established by intravaginal (i.vg.) inoculation of yeast cells in mice maintained in pseudoestrus. Fungal CFU in each vagina was determined to assess the severity of infection. Mice vaccinated before infection developed about 62% fewer vaginal CFU than nonimmunized controls. Naive mice that received polyclonal antiserum (from vaccinated mice) i.vg. before infection had 60% fewer CFU than controls. The serum protective factor was stable at 56°C, butC. albicanscells absorbed this factor. Mice given MAb B6.1 i.vg. after infection was established had fewerCandidaCFU in vaginal tissue than control mice given buffer instead of antibody. MAbs B6.1 and B6 given intraperitoneally before infection protected mice, but MAbs preabsorbed with yeast cells did not. MAb B6.1 also protected againstC. tropicalisvaginal infection, but MAb B6 did not. The protective activities of MAbs B6.1 and B6 appeared to be specific because an irrelevant IgM carbohydrate-specific MAb and an irrelevant IgG protein-specific MAb were not protective; also, MAb B6.1 did not affect development of vaginal chlamydial infection. These studies show that an appropriate antibody response, or administration of protective antibodies, can help the host to resistCandidavaginal infection.
Modulation of Expression of the ToxR Regulon in
Vibrio cholerae
by a Member of the Two-Component Family of Response Regulators
Authors: Wong Sandy M. , Carroll Patricia A. , Rahme Laurence G. , Ausubel Frederick M. , Calderwood Stephen B. 
Published: December 2019

ABSTRACT

The ToxRS system in
Vibrio cholerae
plays a central role in the modulation of virulence gene expression in response to environmental stimuli. An integration of multiple signalling inputs mediated by ToxR, -S, and -T controls virulence gene expression leading to cholera toxin (CT) production. Recently, we identified a new virulence locus,
varA
(virulence associated regulator), in classical
V. cholerae
O1 that positively controls transcription of
tcpA
, the major subunit of the toxin-coregulated pilus (TCP) and the production of CT, two key factors in cholera pathogenesis. The
varA
locus is a homolog of
gacA
(originally described for the soil organism
Pseudomonas fluorescens
), which encodes a conserved global regulator belonging to the family of two-component signal transducing molecules. GacA homologs in a number of diverse gram-negative pathogenic bacterial species have been implicated in controlling the production of diverse virulence factors.
varA
mutants showed reduced levels of
tcpA
message and TcpA protein, lacked visible signs of autoagglutination (a phenotype associated with functional TCP), produced decreased levels of CT, and were attenuated in colonizing infant mice. Transcription of
varA
appears to be independent of ToxR, and overexpression of the regulators
tcpPH
and
toxT
from plasmids in the
varA
mutant restored wild-type levels of CT production and the ability to autoagglutinate.
varA
represents an additional modulating factor in the coordinate expression of virulence factors in
V. cholerae.
Evidence for Multiple Pathologic and Protective Mechanisms of Murine Cerebral Malaria
Authors: Jennings Veronica M. , Lal Altaf A. , Hunter Robert L. 
Published: December 2019

ABSTRACTMurine cerebral malaria (CM) induced byPlasmodium bergheiANKA kills susceptible mice within 24 to 48 h of onset of symptoms and is characterized by the production of inflammatory cytokines in the brain. C57BL/6J mice are sensitive to lethal CM, while A/J mice are resistant. These strains of mice were immunized with an adjuvant vaccine of killed whole-blood-stage parasites. The immunization protected C57BL/6 mice from lethal CM following virulent challenge. The same immunization increased the incidence of lethal CM in A/J mice challenged similarly. Histopathologic examination of the brains of mice from these studies revealed two distinct types of lesions. Type I CM is acute in onset; usually lethal; and characterized by widespread microglial activation, endothelial cell damage, and microvascular disruption in the brain. Type II CM is characterized by intense, but focal, mononuclear cell inflammation without endothelial cell damage or microvascular destruction. Animals with type II lesions were clinically normal and protected from type I lesions. Available clinical, epidemiological, and biochemical evidence suggests that type I and type II lesions might exist in human CM as well.
Internalization ofStaphylococcus aureusby Endothelial Cells Induces Apoptosis
Authors: Menzies Barbara E. , Kourteva Iordanka 
Published: December 2019

ABSTRACTThe ability ofStaphylococcus aureusto invade and survive within endothelial cells is believed to contribute to its propensity to cause persistent endovascular infection with endothelial destruction. In the present study, we show that following invasion of human umbilical vein endothelial cells, intracellularS. aureusorganisms remain viable over a 72-h period and, as determined by transmission electron microscopic examination, that the bacteria exist within vacuoles and free within the cytoplasm. We also demonstrate that endothelial cell death followingS. aureusinvasion occurs at least in part by apoptosis as shown by DNA fragmentation and changes in nuclear morphology. Apoptotic changes were evident as early as 1 h after infection of endothelial cells. Internalization ofS. aureusrather than adherence appears to be necessary, since use of the phagocytosis inhibitor cytochalasin D prevented apoptosis. UV-killed staphylococci, although retaining the capacity to be internalized, were not capable of inducing apoptosis, suggesting that apoptosis is dependent upon a factor associated with viable organisms. The studies demonstrate that viable intracellularS. aureusinduces apoptosis of endothelial cells and that internalized staphylococci can exist free within the cytoplasm.
Identification of the
Helicobacter pylori
VacA Toxin Domain Active in the Cell Cytosol
Authors: de Bernard Marina , Burroni Daniela , Papini Emanuele , Rappuoli Rino , Telford John , Montecucco Cesare 
Published: December 2019

ABSTRACT

Cells exposed to
Helicobacter pylori
toxin VacA develop large vacuoles which originate from massive swelling of membranous compartments at late stages of the endocytic pathway. When expressed in the cytosol, VacA induces vacuolization as it does when added from outside. This and other evidence indicate that VacA is a toxin capable of entering the cell cytosol, where it displays its activity. In this study, we have used cytosolic expression to identify the portion of the toxin molecule responsible for the vacuolating activity. VacA mutants with deletions at the C and N termini were generated, and their activity was analyzed upon expression in HeLa cells. We found that the vacuolating activity of VacA resides in the amino-terminal region, the whole of which is required for its intracellular activity.