bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fe(III)‐mediated cellular toxicity
Authors: Chamnongpol Sangpen , Dodson Walter , Cromie Michael J. , Harris Z. Leah , Groisman Eduardo A. 
Published: March 2003

SummaryBecause it can undergo reversible changes in oxidation state, iron is an excellent biocatalyst but also a potentially deleterious metal. Iron‐mediated toxicity has been ascribed to Fe(II), which reacts with oxygen to generate free radicals that damage macromolecules and cause cell death. However, we now report that Fe(III) exhibits microbicidal activity towards strains of Salmonella enterica, Escherichia coli and Klebsiella pneumoniae defective in the Fe(III)‐responding PmrA/PmrB signal transduction system. Fe(III) bound to a pmrA Salmonella mutant more effectively than to the isogenic wild‐type strain and exerted its microbicidal activity even under anaerobic conditions. Moreover, Fe(III) permeabilized the outer membrane of the pmrA mutant, rendering it susceptible to vancomycin, which is normally non‐toxic to Gram‐negative species. On the other hand, Fe(III) did not affect the viability of a mutant defective in Fur, the major regulator of cytosolic iron homeostasis, which is hypersensitive to Fe(II)‐mediated toxicity. A functional pmrA gene was necessary for bacterial survival in soil. Our results indicate that Fe(III) exerts its microbicidal activity by a mechanism that is oxygen independent and different from that mediated by Fe(II).
Conflicting needs for a Salmonella hypervirulence gene in host and non‐host environments
Authors: Mouslim Chakib , Hilbert Friederike , Huang Henry , Groisman Eduardo A. 
Published: March 2003

SummaryThe Gram‐negative pathogen Salmonella enterica harbours a periplasmic D‐Ala‐D‐Ala dipeptidase (termed PcgL), which confers the ability to grow on D‐Ala‐D‐Ala as sole carbon source. We now demonstrate that inactivation of the pcgL gene renders Salmonella hypervirulent. This phenotype results from the accumulation of peptidoglycan‐derived D‐Ala‐D‐Ala in the pcgL mutant and not from an intrinsically faster growth rate. Synthetic D‐Ala‐D‐Ala (but not L‐Ala‐L‐Ala or D‐Ala) increased the number of wild‐type Salmonella in the liver and spleen of mice within 24 h of injection, suggesting that D‐Ala‐D‐Ala interferes with some aspect of innate immunity. However, the pcgL mutant was unable to grow on D‐Ala‐D‐Ala as sole carbon source and was defective for survival in nutrient‐poor conditions. We identified clinical isolates lacking D‐Ala‐D‐Ala dipeptidase activity and unable to grow on D‐Ala‐D‐Ala because of inactivation of the pcgL gene. Our data suggest that genes (such as pcgL) that, when mutated make pathogens more virulent, may be retained because their contribution to pathogen fitness in non‐host environments outweighs potential advantages of the hypervirulent vari‐ant in the infected host.
Characterization of Cah, a calcium‐binding and heat‐extractable autotransporter protein of enterohaemorrhagic Escherichia coli
Authors: Torres Alfredo G. , Perna Nicole T. , Burland Valerie , Ruknudin Abdul , Blattner Fred R. , Kaper James B. 
Published: March 2003

SummaryWe have identified and characterized a protein of enterohaemorrhagic Escherichia coli (EHEC) serotype O157:H7 that shares homology with antigen 43 and AIDA‐I of E. coli. The gene encoding this protein consists of a 2850 bp open reading frame and was named cah for calcium binding antigen 43 homologue. The prototype EHEC strain EDL933 possesses identical duplicate copies of cah (cah1 and cah2), which showed 100% identity at the nucleotide level. We showed that E. coli K‐12 containing the recombinant cah gene produced two proteins, an ≈ 80 kDa outer membrane protein and a 43.0 kDa heat‐extractable protein. The Cah protein contains a predicted 52‐amino‐acid extended signal sequence found in several autotransporter proteins, and N‐terminal sequencing data indicated that the 43.0 kDa passenger protein was derived from cleavage of the signal sequence from alanine at position 53. Phenotypes such as autoaggregation and change in bacterial shape were observed when a recombinant plasmid containing the cah gene was introduced into a laboratory E. coli strain, and these phenotypes were eliminated upon mutation of the cah gene. The passenger domain contains six domains found in calcium‐binding proteins, and the recombinant Cah passenger protein bound 45Ca2+. In E. coli O157:H7, Cah is a heat‐extractable protein, the expression of which is induced in minimal essential media and under divalent ion‐depleting conditions; it also participates in the formation of biofilms. Our results provide insight into the expression, secretion and preliminary features of the calcium‐binding Cah autotransporter protein of EHEC O157:H7.
A Salmonella SipB‐derived polypeptide blocks the ‘trigger’ mechanism of bacterial entry into eukaryotic cells
Authors: Hayward Richard D. , Hume Peter J. , McGhie Emma J. , Koronakis Vassilis 
Published: March 2003

SummaryEntry into non‐phagocytic mammalian cells by the invasive pathogens Salmonella and Shigella is triggered by the delivery of bacterial virulence effector proteins into the host cell. This is dependent upon Salmonella SipB or its Shigella homologue IpaB, which insert into the eukaryotic cell plasma membrane. Here we show that a SipB‐derived 166 residue α‐helical polypeptide is a potent inhibitor of SipB‐directed liposome fusion in vitro, preventing the membrane‐associated form of SipB from inserting deeply into the bilayer. This polypeptide blocks Salmonella entry into cultured mammalian cells at 10−10 M, and is a heterologous inhibitor of analogous IpaB activity and Shigella cell entry. These findings reveal a potential strategy to identify inhibitors of the ‘trigger’ mechanism underlying cell entry by these major invasive pathogens.
IHF and HU stimulate assembly of pre‐replication complexes at Escherichia coli oriC by two different mechanisms
Authors: Ryan Valorie T. , Grimwade Julia E. , Nievera Christian J. , Leonard Alan C. 
Published: March 2003

SummaryPre‐replication complexes (pre‐RC) assemble on replication origins and unwind DNA in the presence of chromatin proteins. As components of Escherichia coli pre‐RC, two histone‐like proteins HU and IHF (integration host factor), stimulate initiator DnaA‐catalysed unwinding of the chromosomal replication origin, oriC. Using in vivo footprint analysis just before DNA synthesis initiates, we detect IHF binding coincident with a shift of DnaA to weaker central oriC sites. Integration host factor redistributed pre‐bound DnaA to identical sites in vitro. HU did not redistribute DnaA, but suppressed binding specifically at I3. These results suggest that different pathways mediated by bacterial chromatin proteins exist to regulate pre‐RC assembly and unwind oriC.
Inducible bacteriocin production in Lactobacillus is regulated by differential expression of the pln operons and by two antagonizing response regulators, the activity of which is enhanced upon phosphorylation
Authors: Diep Dzung B. , Myhre Ronny , Johnsborg Ola , Aakra Ågot , Nes Ingolf F. 
Published: March 2003

SummaryExpression of the five (pln) operons involved in the bacteriocin production of Lactobacillus plantarum C11 is regulated by a so‐called pheromone‐based signal‐transducing network, in which the peptide pheromone (PlnA) induces bacteriocin production through the action of a histidine protein kinase (PlnB) and two antagonizing response regulators (PlnC as an activator and PlnD as a negative regulator). All pln‐regulated promoters contain a conserved pair of direct repeats that serve as binding sites for PlnC and PlnD. In the present work, we show that the five PlnA‐responsive operons are differentially expressed with regard to both timing and strength, and that the pheromone triggers a strong autoactivating loop of the regulatory unit (plnABCD) during an early stage of induction that gradually leads to enhanced activa‐tion of the other operons. The transport operon (plnGHSTUV), which is involved in the secretion of the pheromone and bacteriocins, is also expressed relatively early upon induction, but is quickly turned off soon after peak expression. Further investigation of the various promoters revealed that, although subtle differences within the promoter regions could account for the observed differential regulation, the presence of a downstream promoter‐proximal se‐quence in one promoter was found to cause delayed peak activity. How phosphorylation regulates the activity of the pln response regulators was also accessed by direct mutagenesis at their phosphorylation sites. It was found that the two response regulators exert activity at two different levels: a low level when they are not phosphorylated and an elevated level when they are phosphorylated. The present data demonstrate that bacteriocin production in L. plantarum C11 is a highly regulated process, in which different regulatory mechanisms are applied to fine tune the timing and strength of expression of the five pln operons.
Conservation of a gene conversion mechanism in two distantly related paralogues of Anaplasma marginale
Authors: Meeus Patrick F. M. , Brayton Kelly A. , Palmer Guy H. , Barbet Anthony F. 
Published: March 2003

SummaryAnaplasmataceae, the causative agents of anaplasmosis and ehrlichiosis, persist in the bloodstream of their mammalian hosts, allowing acquisition and transmission by tick vectors. Anaplasma marginale establishes persistent infection characterized by sequential cycles of rickettsaemia in which new antigenic variants emerge. The two most immunodominant outer membrane proteins, MSP2 and MSP3, are paralogues, each encoded by a distinct family of related genes. This study demonstrates that, although the two gene families have diverged substantially, each has maintained a similar mechanism to generate structurally and antigenically polymorphic surface antigens. Like MSP2, MSP3 is expressed from a single locus in which variation of the expressed msp3 gene is generated by recombination using msp3 pseudogenes. Each of the msp3 pseudogenes encodes a unique central variable region (CVR) flanked by conserved 5′ and 3′ regions. Changes in the CVR of the expressed msp3, concomitant with invariance of the pseudogenes, indicate that expression site variation is generated using gene conversion. A. marginale thus maintains two large, separate systems within its small genome to generate antigenic variation of its surface proteins, while analogous structural elements indicate a common mechanism.
Comparative genomics reveal novel heat shock regulatory mechanisms in Staphylococcus aureus and other Gram‐positive bacteria
Authors: Chastanet Arnaud , Fert Juliette , Msadek Tarek 
Published: March 2003

SummaryMultiple regulatory mechanisms for coping with stress co‐exist in low G+C Gram‐positive bacteria. Among these, the HrcA and CtsR repressors control distinct regulons in the model organism, Bacillus subtilis. We recently identified an orthologue of the CtsR regulator of stress response in the major pathogen, Staphylococcus aureus. Sequence analysis of the S. aureus genome revealed the presence of potential CtsR operator sites not only upstream from genes encoding subunits of the Clp ATP‐dependent protease, as in B. subtilis, but also, unexpectedly, within the promoter regions of the dnaK and groESL operons known to be specifically controlled by HrcA. The tandem arrangement of the CtsR and HrcA operators suggests a novel mode of dual heat shock regulation by these two repressors. The S. aureus ctsR and hrcA genes were cloned under the control of the PxylA xylose‐inducible promoter and used to demonstrate dual regulation of the dnaK and groESL operons by both CtsR and HrcA, using B. subtilis as a heterologous host. Direct binding by both repressors was shown in vitro by gel mobility shift and DNase I footprinting experiments using purified S. aureus CtsR and HrcA proteins. ΔctsR, ΔhrcA and ΔctsRΔhrcA mutants of S. aureus were constructed, indicating that the two repressors are not redundant but, instead, act together synergistically to maintain low basal levels of expression of the dnaK and groESL operons in the absence of stress. This novel regulatory mode appears to be specific to Staphylococci.
The conserved cytoplasmic module of the transmembrane chemoreceptor McpC mediates carbohydrate chemotaxis in Bacillus subtilis
Authors: Kristich Christopher J. , Glekas George D. , Ordal George W. 
Published: March 2003

Summary Escherichia coli
cells use two distinct sensory circuits during chemotaxis towards carbohydrates. One circuit requires the phosphoenolpyruvate‐dependent phosphotransferase system (PTS) and is independent of any specific chemoreceptor, whereas the other uses a chemoreceptor‐dependent sensory mechanism analogous to that used during chemotaxis towards amino acids. Work on the carbohydrate chemotaxis sensory circuit of
Bacillus subtilis
reported in this article indicates that the
B. subtilis
circuit is different from either of those used by
E. coli
. Our chemotactic analysis of
B. subtilis
strains expressing various chimeric chemoreceptors indicates that the cytoplasmic, C‐terminal module of the chemoreceptor McpC acts as a sensory‐input element during carbohydrate chemotaxis
. Our results also indicate that PTS‐mediated carbohydrate transport, but not carbohydrate metabolism, is required for production of a chemotactic signal. We propose a model in which PTS‐transport‐induced chemotactic signals are transmitted to the C‐terminal module of McpC for control of chemotaxis towards PTS carbohydrates.
Fedotozine, a kappa‐opioid agonist, prevents spinal and supra‐spinal Fos expression induced by a noxious visceral stimulus in the rat
Authors: Bonaz  , Rivière  , Sinniger  , Pascaud  , Junien  , Fournet  , Feuerstein  
Published: March 2003

Fedotozine, a kappa opioid agonist, reverses digestive ileus caused by acetic acid (AA)‐induced visceral pain in rats. The aims of this study were: to map, in conscious rats, central pathways activated by AA using Fos as a marker of neuronal activation;  to characterize primary afferent fibres involved in this activation; and  to investigate the effect of fedotozine on AA‐induced Fos expression. AA (0.6%; 10 mL kg–1) was injected i.p. in conscious rats either untreated; pretreated 14 days before with capsaicin; pretreated 20 min previously with fedotozine; or pretreated 2 h prior to fedotozine with the κ‐antagonist nor‐binaltorphimine (nor‐BNI). Controls received the vehicle alone. 60 min after injection of AA, rats were processed for Fos immunohistochemistry. Visceral pain was assessed by counting abdominal cramps. AA induced Fos in the thoraco‐lumbar spinal cord (laminae I, V, VII and X) and numerous brain structures such as the nucleus tractus solitarius, and paraventricular nucleus (PVN) of the hypothalamus, whereas almost no Fos labelling was observed in controls. Capsaicin pretreatment blocked AA‐induced Fos in all structures tested. Fedotozine significantly decreased AA‐induced abdominal cramps and Fos immunoreactivity in the spinal cord and PVN, this effect being reversed by nor‐BNI pretreatment.AA induces Fos in the spinal cord and numerous brain nucuei, some of which are involved in the control of digestive motility in rats. This effect is mediated through capsaicin‐sensitive afferent fibres and prevented by fedotozine most likely through a peripheral action on visceral afferents.
A nutrient drink test to assess maximum tolerated volume and postprandial symptoms: effects of gender, body mass index and age in health
Authors: Chial H. J. , Camilleri C. , Delgado‐Aros S. , Burton D. , Thomforde G. , Ferber I. , Camilleri M. 
Published: March 2003

Abstract

To assess the effects of age, gender and body mass index on the maximum tolerated volume of a nutrient drink and postprandial symptoms in health. Healthy adolescents (15 M, 15 F, aged 13–17 years) and adults (15 M, 25 F, aged 19–51 years) ingested Ensure®(1 kcal mL−1) at a rate of 30 mL min−1. The maximum tolerated volume was recorded. Thirty minutes later, bloating, fullness, nausea and pain were rated using visual analogue scales. The Mann–Whitney test was used for comparisons between groups using body mass index and maximum tolerated volume as covariates. Age‐related differences in maximum tolerated volume were noted between adolescents and adults, and were observed in both genders. Adults had higher scores for bloating and pain, and lower scores for fullness. Gender‐related differences in maximum tolerated volume were noted in the group as a whole, and separately for adolescents and adults. Females had higher scores for nausea and pain. Gender and age‐related differences in the maximum tolerated volume of a nutrient drink and postprandial symptoms should be considered in future studies of upper gastrointestinal symptoms in disease. Body mass index does not appear to influence maximum tolerated volume beyond its association with age and gender.
In search of objective manometric criteria for colonic high‐amplitude propagated pressure waves
Authors: De Schryver A. M. P. , Samsom M. , Smout A. J. P. M. 
Published: March 2003

Abstract
The aims of this study were to explore all characteristics of high‐amplitude propagated contractions (HAPCs) that would allow them to be distinguished from nonHAPC colonic pressure waves, and to develop computer algorithms for automated HAPC detection. Colonic manometry recordings obtained from 24 healthy volunteers were used. Automated analysis was performed to detect propagated pressure waves and to determine their amplitude, duration and area under the curve (AUC). For each of these variables distribution plots were made. Automated HAPC counts were compared to visual counts by experienced investigators. Distribution plots of 141093 colonic pressure waves lacked a bimodal pattern, as was also the case for propagated contractions (n = 8758). With increasing high‐amplitude thresholds for HAPC detection, a gradual decrease in the automatically detected HAPC number was observed. These findings precluded determination of a threshold. Taking visually detected HAPCs as reference, amplitude thresholds of 100 mmHg in two channels, and 80 mmHg in one channel yielded the highest sensitivity (92%). In conclusion, objective criteria to distinguish HAPCs from other propagated pressure waves on the basis of their amplitude, duration or AUC do not exist. Automated detection of HAPCs using empirically derived criteria leads to an acceptable degree of correlation with visually detected HAPCs.
Fractionator analysis shows loss of neurons in the lateral geniculate nucleus of macaques infected with neurovirulent simian immunodeficiency virus
Authors: Berman  , Raymond  , Warren  , Raghavan  , Joag  , Narayan  , Cheney  
Published: March 2003

N.E.J. Berman, L.A. Raymond, K.A. Warren, R. Raghavan, S.V. Joag, O. Narayan and P.D. Cheney† (1998) Neuropathology and Applied Neurobiology24, 44–52Fractionator analysis shows loss of neurons in the lateral geniculate nucleus of macaques infected with neurovirulent simian immunodeficiency virusInfection of macaques with neurovirulent strains of simian immunodeficiency virus (SIVmac) is an experimental model for the neurological manifestations of AIDS. Loss of neurons has been reported in the cerebral cortex following immunodeficiency viral infection, but thalamic structures which may contribute to electrophysiological changes and neurological deficits have not been examined. In this study, the lateral geniculate nucleus (LGN) of macaques inoculated with macrophage‐tropic, neurovirulent virus SIVmac239 (R71 and 17E) was examined for neuron loss using the optical fractionator method. Estimates of the number of neurons in the P layers of the lateral geniculate nucleus of age‐matched control macaques ranged from 1.0 to 1.3 × 106, while the number of neurons in SIV infected macaques ranged from 0.8 to 1.1 × 106, reflecting neuron loss of up to 28%. Neuron loss was not observed in the magnocellular layers. The total number of glia and glial density were unchanged. Loss of neurons in the lateral geniculate nucleus was correlated with the pattern of neuropathological changes. Neuron loss was most severe in animals with encephalitis concentrated in the brain stem and subcortical white matter and was less apparent in animals with diffuse encephalitis. Neuron loss in the lateral geniculate nucleus did not explain changes observed in the visual evoked potential, which was severely affected in two animals which showed a loss of 24 and 26%, while it was normal in a third animal which showed neuron loss of 28%.
The pathology of the spinal cord in progressive supranuclear palsy
Authors: Vitaliani R. , Scaravilli T. , Scaravilli F. , An S. F. , Pramstaller P. P. 
Published: March 2003

Introduction:  We describe the results of a study of the spinal cord of five patients with progressive supranuclear palsy (PSP).Materials and methods:  Routine, immuno‐histochemical and morphometric methods were used.Results:  Examination of the sixth cervical, seventh thoracic and fifth lumbar segments revealed a variable degree of gliosis and density of neuropil threads (NTs), nerve cell loss and diffuse presence of tau‐positive cytoplasmic staining of neurons, some of which were reminiscent of neurofibrillary tangles (NFTs) and predominated in laminae V–VII and X of the cord. Morphometric study revealed 47, 52 and 32% decrease in cell numbers in the motor area (lamina IX) at the three spinal levels, respectively, and 39% in the intermediolateral column.Conclusions:  This is the first report describing severe neuronal loss throughout the whole spinal cord in patients with PSP and its results are in keeping with a previous study of the nucleus of Onufrowicz. We analyse the reasons why cell loss fails to produce clinical symptoms, and consider the clinicopathological correlations between anatomical changes and dystonia. On the basis of existing data, we conclude that previous suggestions, implicating spinal interneurons in the pathogenesis of dystonia, should not be supported.